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Title: The philosophy of biology
Author: Johnstone, James Johnstone, chevalier de
Language: English
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THE PHILOSOPHY OF BIOLOGY
CAMBRIDGE UNIVERSITY PRESS
London: FETTER LANE, E.C.
C. F. CLAY, Manager
[Illustration]
Edinburgh: 100 PRINCES STREET
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Leipzig: F. A. BROCKHAUS
New York: G. P. PUTNAM’S SONS
Bombay and Calcutta: MACMILLAN AND CO., LTD.
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_All rights reserved_
THE PHILOSOPHY
OF
BIOLOGY
BY
JAMES JOHNSTONE, D.Sc.
Cambridge:
at the University Press
1914
INTRODUCTION
It has been suggested that some reference, of an apologetic nature,
to the title of this book may be desirable, so I wish to point out
that it can really be justified. Science, says Driesch, is the
attempt to describe Givenness, and Philosophy is the attempt to
understand it. It is our task, as investigators of nature, to describe
what seems to us to happen there, and the knowledge that we so
attain--that is, our perceptions, thinned out, so to speak, modified
by our mental organisation, related to each other, classified and
remembered--constitutes our Givenness. This is only a description
of what seems to us to be nature. But few of us remain content with
it, and the impulse to go beyond our mere descriptions is at times
an irresistible one. Fettered by our habits of thought, and by the
limitations of sensation, we seem to look out into the dark and to see
only the shadows of things. Then we attempt to turn round in order that
we might discover what it is that casts the shadows, and what it is in
ourselves that gives shape to them. We seek for the Reality that we
feel is behind the shadows. That is Philosophy.
The Physics of a generation earlier than our own thought that it had
discovered Reality in its conception of an Universe consisting of
atoms and molecules in ceaseless motion. What it described were only
motions and transformations, but it understood these motions and
transformations as matter and energy. Yet more subtle minds than
the great physicists of the beginning of the nineteenth century had
already seen that sensation might mislead us. There was something
in us that continually changed--that was our consciousness, and it
was all that we knew. If external things did exist they existed only
because we thought them. But we ourselves exist, for we are not only
a stream of consciousness that continually changes, but there is in
us a personality, or identity, which has remained the same throughout
all the vicissitudes of our consciousness. If the things that exist
for us exist only because we think them, and if we also exist, then we
must exist in the thought of an Absolute Mind that thinks us. Physical
Science, studying only motions and transformations, understood that
there was something that moved and transformed--this was matter and
energy. Mental Science, studying only thought, understood that nature
was only the thought of an Universal Mind. Either conclusion was
equally valid Philosophy (or metaphysics), and neither could be proved
or disproved by the methods of Science. The speculative game is drawn,
said Huxley, let us get to practical work!
Both Physics and Biology did get to work, with the results that we
know. But Physics advanced far beyond the acquirement of the results
that stimulated Biology to formulate our present hypotheses of
evolution and heredity. As its knowledge accumulated, it began to doubt
whether matter and energy, atoms and molecules, mass and inertia--all
those things which it thought at first were so real--were anything else
after all than ways in which our mental organisation dealt with crude
sensations. They might, as Bergson said later on, be the moulds into
which we pour our perceptions. Physics set up a test of Reality, the
law of the conservation of matter and energy. There are existences
which may or may not persist. Visions and phantasms and dreams are
existences _while they last_. They are true for the mind in which
they occur. But they seem to arise out of nothing, and to disappear
into nothing, and physical Science cannot investigate them. They are
existences which are not conserved. On the other hand those images
which we call moving matter and transforming energy can be investigated
by the methods of physics. Molecules change, but something in them,
the atoms, remain constant. Energy becomes transformed, and it may
even seem to cease to exist, but if it disappears, then something is
changed so that the lost energy can be traced in the nature of the
change. Matter and energy are conserved and therefore they are the only
Realities. But the test is obviously one that has an _a priori_ basis,
and we may doubt whether it is a test of Reality.
Thus Physics constructed a dynamical Universe, that is, one which
consisted of atoms which attracted or repelled each other with forces
which were functions of the distances between them. Even now this
conception of a dynamical, Newtonian Universe is a useful one, though
we recognise that it is only symbolism. But it was not a conception
with which Physics could long remain content. How could atoms separated
from each other by empty space act on each other, that is, how could a
thing act where it was not? There must be something between the atoms.
The Universe could not be a discontinuous one, and so Physics invented
an Universe that was _full_. It was an immaterial, homogeneous,
imponderable, continuous Universe. That which existed behind the
appearances of atoms and molecules and energy was the ether of space.
It must be admitted that the conception appears to the layman to
involve only contradictions: heterogeneous, discontinuous, ponderable
atoms are only singularities in a homogeneous, continuous, imponderable
medium, or ether. Yet it is easy to see that this contradiction arises
in our mind only because we had previously thought of the Universe in
terms of matter and energy, and in spite of ourselves we attempt to
think of the new Reality in terms of the old one. In its attempt to
understand all its later results Physics had therefore to invent a new
Philosophy--that of the ether of space.
It is only in our own times that Biology has become sceptical and has
begun to doubt whether its earlier Philosophy is a sound one. That
which it describes--the object-matter of its Science--is not that which
Physics describes. There are two domains of Givenness, the organic
and the inorganic. Biology, leaning on Physics, studied motions and
transformations, just as Physics did, though the motions which it
studied were more complex and the transformations more mysterious. But
borrowing the methods of investigation of Physics it borrowed also
its Philosophy, and so it placed behind its Givenness the Reality
that Physics at first postulated and then abandoned. The organism was
therefore a material system actuated by energy. The notion, it should
be noted, is not a deduction from the results of Biology, but only from
its methods.
Did Physiology, that is, the Physiology of the Schools, ever really
investigate the organism? A muscle-nerve preparation, an excised kidney
through which blood is perfused, an exposed salivary gland which is
stimulated, even a frog deprived of its cerebral hemispheres--these
things are not organisms. They are not permanent centres of action,
autonomous physico-chemical constellations capable of independent
existence, and capable of indefinite growth by dissociation. They
are parts of the organism, which, having received the impulse of
life, an impulse which soon becomes exhausted, exhibit for a time
some of the phenomena of the organism. What Physiology did attain
in such investigations was an analytical description of some of the
activities of the organism. It did not describe life, but rather
the physico-chemical reactions in which life is manifested. The
description, it should be noted, is all-important for the human race
in its effort to acquire mastery over its environment; and there is
no other way in which it may be carried further but by the methods of
physical Science. Givenness is one, though we arbitrarily divide it
into the domains of the organic and the inorganic, and there can be
only one way of describing it. That is the mechanistic method.
Nevertheless all this is only a description, and our Philosophy
must be the attempt to understand our description. The mechanistic
biologist, in the attempt to identify his Philosophy with that of
a former generation of physicists, says that he is describing a
physico-chemical aggregate--an assemblage of molecules of a high degree
of complexity--actuated by energy, and undergoing transformations. But
our scepticism as to the validity of this conclusion is aroused by
reflecting on its origin. If it was borrowed from the Philosophy of a
past Physics, and if the more penetrating analysis of the Physics of
our own time has made a new Philosophy desirable, should not Biology
also revise its understanding of its descriptions? For Biology has
not stood still any more than Physics, and the Physiology of our own
day has become different from that of the times when the mechanistic
Philosophy of life took origin. The embryologists and the naturalists
of our own generation have studied the _whole_ organism in its normal
functioning and behaviour, and have obtained results which cannot
easily be understood as physico-chemical mechanism. Life is not the
activities of the organism, but the integration of the activities
of the organism, just as Reality for Physics is not the atoms and
molecules of gross matter, but the integration of these in the ether of
space.
This, then, is all that we mean by the philosophy of Biology--the
attempt to understand the descriptions of the Science in the light of
its later investigations. Philosophy, in the academic sense, we have
not considered in relation to the subject-matter of our science, though
there is much in the classic systems that is of absorbing interest,
even to the working investigator of the nineteenth century. The
biological education is not, however, such as to predispose one towards
these studies. The reader will recognise that the point of view, and
the methods of treatment, adopted in this book are those suggested by
Driesch and Bergson, even if no references are given. He may, perhaps,
appreciate this limitation; for, influenced by the modern scientific
training, he may be inclined to regard Philosophy as Mark Twain
regarded his Egyptian mummy: if he is to have a corpse it might as well
be a real fresh one.
J. J.
LIVERPOOL
_November 1913_
CONTENTS
CHAPTER I
PAGE
THE CONCEPTUAL WORLD 1
_Argument._--The conscious organism is one that acts. Its
consciousness of an external world is not simply the result of
the stimuli made by that world on its organs of sense, for it becomes
fully aware only of those stimuli which result in deliberated bodily
activity. This awareness of an outer world on which it acts is the
perception of the organism. Its consciousness is an intensive
multiplicity. This multiplicity is arbitrarily dissociated, for
convenience’ sake, by the mental organisation, which confers extension
and magnitude and succession on those aspects of consciousness
which it arbitrarily dissociates from each other. Our notion of
space is an intuitive one and depends on our modes of bodily
exertion. Our notions of motion and continuity are also intuitive
ones, and they cannot be represented intellectually, but we can
approximate to them by the methods of the infinitesimal calculus.
Mathematical time is only a series of standard events which punctuate
our duration. Duration is the accumulated existence and
experience of the organism. We cannot prove intellectually that
there is a world external to our consciousness, but that this world
exists is a conviction intuitively held.
CHAPTER II
THE ORGANISM AS A MECHANISM 49
_Argument._--If the organism is a physico-chemical mechanism its
activities must conform to the two principles of energetics: the law
of conservation of energy and matter, and the law of entropy-increase.
They conform strictly to the law of conservation.
The law of the degradation of energy is true of our experience
of inorganic nature, but we can show that it cannot be universally
true. Inorganic processes are irreversible ones, and they proceed
in one direction only, and in them energy is degraded. Organic
processes, that is, the processes carried on in the generalised
organism, are irreversible; or, at least, there is a tendency for
them to be carried on without necessary dissipation of energy.
CHAPTER III
THE ACTIVITIES OF THE ORGANISM 83
_Argument._--If the organism is investigated by the methods of
physical and chemical science, nothing but physico-chemical
activities can be discovered. This is necessarily the case, since
methods which yield physico-chemical results only are employed.
The physiologist makes an analysis of the activities of the organism,
and he reduces these activities to certain categories; although all
attempts completely to describe the functioning of the organism
solely in terms of physical and chemical reactions fail. In addition
to the reactions which make up the functioning of an organ or
organ-system, there is direction and co-ordination of these reactions.
The individual physico-chemical reactions which occur in the
functioning of the organism are integrated, and life is not merely
these reactions, but also their integration.
CHAPTER IV
THE VITAL IMPETUS 120
_Argument._--The notion of the organism as a physico-chemical
mechanism is a deduction from the methods of physiology, and
not from its results. The notion of vitalism is a natural or
intuitive one. The historic systems of vitalism assumed the
existence of a spiritual agency in the organism, or of a form of
energy which was peculiar to the activities of the organism.
Modern investigation lends no support to either belief. But the
study of the organism as a whole, that is, the study of developmental
processes, or that of the organism acting as a whole, afford a
logical disproof of pure mechanism. It shows that there cannot
be a functionality, in the mathematical sense, between the inorganic
agencies that affect the whole organism and the behaviour or
functioning of the whole organism. Mechanism is only suggested
in the study of isolated parts of the organism. We are compelled
toward the belief that there is an agency operative in the activities
of the organism which does not operate in purely inorganic becoming.
This is the Vital Impetus of Bergson, or the Entelechy of
Driesch.
CHAPTER V
THE INDIVIDUAL AND THE SPECIES 162
_Argument._--The concept of the organic individual is one which
is arbitrary, and is convenient only for purposes of description.
Life on the earth is integrally one. Personality is the intuition of
the conscious organism that it is a centre of action, and that all the
rest of the universe is relative to it. The individual organism,
regarded objectively, is an isolated, autonomous constellation,
capable of indefinite growth by dissociation, differentiation, and
re-integration. This growth is reproduction. The dissociated
part reproduces the form and manner of functioning of the individual
organism from which it has proceeded. The offspring varies
from the parent organism, but it resembles it much more than it
varies from it. There are therefore categories of organisms in
nature the individuals of which resemble each other more than they
resemble the individuals belonging to other categories: these are
the elementary species. Hypotheses of heredity are corpuscular
ones, and are based on the physical analogy of molecules and
atoms. The concept of the species is a logical one. The organism
is a phase in an evolutionary or a developmental flux, and the idea
of the species is attained by arresting this flux.
CHAPTER VI
TRANSFORMISM 208
_Argument._--A reasoned classification of organisms suggests that
a process of evolution has taken place. It suggests logical relation-
ships between organisms, while the results of embryology and
palæontology suggest chronological relationships. Yet this kinship
of organisms might only be a logical, and not a material
one. Evolution may have occurred somewhere, but it might be
argued that the ideas of species have generated each other in a
Creative Thought. But transformism may be produced experimentally,
and so science has adopted a mechanistic hypothesis of
the nature of the process. Transformism of species depends on
the occurrence of variations, but these arise spontaneously and
independently of each other, and they must be co-ordinated.
This co-ordination of variations cannot be the work of the environ
ment. Variations are cumulative, and they exhibit direction, and
this direction is either an accidental one, or it is the expression of
an impetus or directing agency in the varying organism itself.
The problem of the cause of variation is only a pseudo-problem.
CHAPTER VII
THE MEANING OF EVOLUTION 245
_Argument._--If we assume the existence of an evolutionary
process, the results of morphology, embryology, and palæontology
ought to enable us to trace the directions followed during this
process. But these results are still so uncertain that they indicate
only a few main lines of transformism. Phylogenetic trees are
largely conjectural in matters of detail. Evolution has resulted in
the establishment of several dominant groups of organisms--the
metatrophic bacteria, the chlorophyllian organisms, the arthropods,
and the vertebrates. Each of these groups displays certain
characters of morphology, energy-transformation, and behaviour;
and a certain combination of characters is concentrated in each of
the groups. But there is a community of character in all organisms
which have arisen during the evolutionary process. The transformation
of kinetic into potential energy is characteristic of the
chlorophyllian organisms. The utilisation of potential energy,
and its conversion into the kinetic energy of regulated bodily
activity, by means of a sensori-motor system, is characteristic of
the animal. The bacteria carry to the limit the energy-transformations
begun in the tissues of the plants and animals. Immobility
and unconsciousness characterise the plant, mobility and consciousness
the animal. Animals indicate two types of actions--intelligent
actions and instinctive actions. Instinctive activity
involves the habitual exercise of modes of action that have been
inherited. Intelligent activities involve the exercise of modes of
action that are not inherited, but which are acquired by the
animal during its own lifetime, and are the results of perceptions
which show the animal that its activity is relative to an outer
environment.
CHAPTER VIII
THE ORGANIC AND THE INORGANIC 289
_Argument._--A strictly mechanistic hypothesis of evolution
compels us to regard the organic world, and the inorganic environment
with which it interacts, as a physico-chemical system. All
the stages of an evolutionary process must therefore be equally
complex: they are simply phases, or rearrangements, of the
elements of a transforming system. The physics on which these
mechanistic hypotheses were based was that of a discontinuous,
granular, Newtonian universe, that is, one consisting of discrete
particles, or mass-points, attracting or repelling each other with
forces which are functions of the distances between them. It was
a spatially extended system of parts. Therefore at all stages in
an evolutionary process, or one of individual development, the
elements of the system constitute an extensive manifoldness, and
the obligation of mechanistic hypotheses of evolution and development
to accept this view has shaped modern theories of heredity.
Life is an intensive manifoldness, but in individual or racial evolu-
tion this intensive manifoldness becomes an extensive manifoldness.
Life is a bundle of tendencies which can co-exist, but which
cannot all be fully manifested, in the same material constellation,
therefore these tendencies become dissociated in the evolutionary
process. In this dissociation there is direction and co-ordination,
which are the Vital Impetus of Bergson, or the Entelechy of
Driesch.
Entelechy is an elemental agency in nature which we are
compelled to postulate because of the failure of mechanism. It is
not spirit, nor a form of energy, but the direction and co-ordination
of energies. There is a sign, or direction of inorganic happening
which absolutely characterises the processes which are capable of
analysis by physico-chemical methods of investigation, and the
result of this direction of inorganic happening is material inertia.
Yet this direction cannot be universal: it must be evaded somewhere
in the universe. It is evaded by the organism.
The problem of the nature of life is only a pseudo-problem.
APPENDIX
MATHEMATICAL AND PHYSICAL NOTIONS 342
Infinity and the notion of the limit. Functionality. Frequency
distributions and probability. Matter, force, mass, and inertia.
Energy-transformations. Isothermal and adiabetic transformations.
The Carnot engine and cycle. Entropy. Inert matter.
INDEX 377
THE PHILOSOPHY OF BIOLOGY
CHAPTER I
THE CONCEPTUAL WORLD
Let us suppose that we are walking along a street in a busy town;
that we are familiar with it, and all the things that are usually to
be seen in it, so that our attention is not likely to be arrested by
anything unusual; and let us further suppose that we are thinking
about something interesting but not intellectually difficult. In
these circumstances all the sights of the town, and all the turmoil
of the traffic fail to impress us, though we are, in a vague sort of
way, conscious of it all. Electric trams approach and recede with a
grinding noise; a taxicab passes and we hear the throb of the engine
and the hooting of the horn, and smell the burnt oil; a hansom comes
down the street and we hear the rhythmic tread of the horse’s feet and
the jingle of the bells; we pass a florist’s shop and become aware
of the colour of the flowers and of their odour; in a café a band
is playing “ragtime.” There are policemen, hawkers, idlers, ladies
with gaily coloured dresses and hats, newsboys, a crowd of people
of many characteristics. It is all a flux of experience of which we
are generally conscious without analysis or attention, and it is a
flux which is never for a moment quite the same, for everything in
it melts and flows into everything else. The noise of the tram-cars
is incessant, but now and then it becomes louder; the music of the
orchestra steals imperceptibly on our ears and as imperceptibly fades
away; the smell of the flowers lingers after we pass the shop, and we
do not notice just when we cease to be conscious of it; the rhythm of
the ragtime continues to irritate after we have ceased to hear the
band--all the sense-impressions that we receive melt and flow over
into each other and constitute our stream of consciousness, and this
changes from moment to moment without gap or discontinuity. It is not
a condition of “pure sensation,” but it is as nearly such as we can
experience in our adult intellectual life.
It is easy to discover that many things must have occurred in the
street which did not affect our full consciousness. We may learn
afterwards that we have passed several friends without recognising
them; we may read in the newspapers about things that happened that
we might have seen, but which we did not see; we may think we know
the street fairly well, but we find that we have difficulty in
recalling the names of three contiguous shops in it; if we happen to
see a photograph which was taken at the time we passed through the
street we are usually surprised to find that there were many things
there that we did not see. Why is it, then, that so much that might
have been perceived by us was not really perceived? We cannot doubt
that everything that came into the visual fields of our eyes must
have affected the terminations of the optic nerves in the retinas;
the complex disturbances of the air in the street must have set our
tympanic membranes in motion; and all the odoriferous particles inhaled
into our nostrils must have stimulated the olfactory mucous membranes.
In all these cases the stimulation of the receptor organs must have
initiated nervous impulses, and these must have been propagated along
the sensory nerves, and must have reached the brain, affecting masses
of nerve cells there. Nothing in physiology seems to indicate that we
can inhibit or repress the activity of the distance sense-receptors,
visual, auditory, and olfactory, with their central connections in
the brain; they must have functioned, and must have been physically
affected by the events that took place outside ourselves, and yet
we were unconscious, in the fullest sense of this term, of all this
activity. Why is it, then, that our perception was so much less
than the actual physical reception of external stimuli that we must
postulate as having occurred? Sherlock Holmes would have said that we
really saw and heard all these things although we did not observe them,
but the full explanation involves a much more careful consideration of
the phenomena of perception than this saying indicates.
There is, of course, no doubt that we did see and hear and smell
all the things that occurred in the street during our aimless
peregrination, that is, all the things which so happened that they
were capable of affecting our organs of sense. This is true if we
mean by seeing and hearing and smelling merely the stimulation of the
nerve-endings of the visual, auditory, and olfactory organs, and the
conduction into the brain of the nervous impulses so set up. But merely
to be stimulated is only a part of the full activity of the brain; the
stimulus transmitted from the receptor organs must result in some kind
of bodily activity if it is to affect our stream of consciousness.
Two main kinds of activity are induced by the stimulation of a
receptor organ and a central ganglion, (1) those which we call reflex
actions, and (2) those actions which we recognise as resulting from
deliberation. We must now consider what are the processes that are
involved in these kinds of neuro-muscular activity.
The term “reflex action” is one that denotes rather a scheme of
sensori-motor activity than anything that actually happens in the
animal body; it is a concept that is useful as a means of analysis of
complex phenomena. In a reflex three things happen, (1) the stimulation
of a receptor organ and of the nerve connecting this with the brain,
(2) the reflection, or shunting, of the nervous impulse so initiated
from the _terminus ad quem_ of the afferent or sensory nerve, to
the _terminus a quo_ of the efferent or motor nerve, and (3) the
stimulation of some effector organ, say a motor organ or muscle, by
the nervous impulse so set up. The simplest case, perhaps, of a reflex
is the rapid closure of the eyelids when something, say a few drops of
water, is flicked into the face. Stated in the way we have stated it
the simple reflex does not exist. In the first place, it is a concept
based on the structural analysis of the complex animal where the body
is differentiated to form tissues--receptor organs, nerves, muscles,
glands, and so on. But a protozoan animal, a _Paramœcium_ for instance,
responds to an external stimulus by some kind of bodily activity, and
yet it is a homogeneous, or nearly homogeneous, piece of protoplasm,
and this simple protoplasm acts at the same time as receptor organ,
conducting tissue or nerve, and effector organ. In the higher animal
certain parts of the integument are differentiated so as to form visual
organs, and the threshold of these for light stimuli is raised while it
is lowered for other kinds of physical stimuli. Similarly other parts
of the integument are modified for the reception of auditory stimuli,
becoming more susceptible for these but less susceptible for other
kinds of stimuli than the adjacent parts of the body. Within the body
itself certain tracts of protoplasm are differentiated so that they
can conduct molecular disturbances set up in the receptor organs in
the integument better than can the general protoplasm; these are the
nerves. Other parts are modified so that they can contract or secrete
the more easily; these are the muscles and glands. The conception
of a reflex action, as it is usually stated in books on physiology,
therefore includes this idea of the differentiation of the tissues, but
all the processes that are included in the typical reflex are processes
which can be carried on by undifferentiated protoplasm.
It is also a schematic description that assumes a simplicity that does
not really exist. As a rule a reflex is initiated by the stimulation
of more than one receptor organ, and the impulses initiated may thus
reach the central nervous system by more than one path. There is no
simple shunting of the afferent impulse from the cell in which it
terminates into another nerve, when it becomes an efferent impulse;
but, instead of this, the impulse may “zigzag” through a maze of paths
in the brain or spinal cord connecting together afferent and efferent
nerves and ganglia. Further, the final part of the reflex, the muscular
contraction, is far from being a simple thing, for usually a series
of muscles are stimulated to contract, each of them at the right time
and with the right amount of force, and every contraction of a muscle
is accompanied by the relaxation of the antagonistic muscle. There are
muscles which open the eyelids and others which close them, and the
cerebral impulse which causes the levators to contract at the same time
causes the depressors to relax.
It is quite necessary to remember that the simple reflex is really
a process of much complexity and may involve many other parts and
structures than those to which we immediately direct our attention. But
leaving aside these qualifications we may usefully consider the general
characters of the reflex, regarding it as a common, automatically
performed, restricted bodily action, involving receptor organ, central
nervous organ, and effector organ. There are certain kinds of external
stimuli that continually affect our organs of sense, and there are
certain kinds of muscular and glandular activity that occur “as a
matter of course,” when these stimuli fall on our organs of sense.
The emanation from onions or the vapour of ammonia causes our eyes to
water; the smell of savoury food causes a flow of saliva; and anything
that approaches the face very rapidly causes us to close the eyes.
Reflexes are, in a way, commonly occurring, purposeful and useful
actions, and their object is the maintenance of a normal condition of
bodily functioning.
We dare hardly say that the simple reflex is an unconsciously performed
action, although we are not conscious, in the fullest sense of the
term, of the reflexes that habitually take place in ourselves. But even
in the decapitated frog, which moves its limbs when a drop of acid is
placed on its back, something, it has been said, akin to consciousness
may flash out and light up the automatic activity of the spinal cord.
We must not think of consciousness as that state of acute mentality
which we experience in the performance of some difficult task, or in
some keenly appreciated pleasure, or in some condition of mental or
bodily distress; it is also that dimly felt condition of normality
that accompanies the satisfactory functioning of the parts of the
bodily organism. But this dim and obscure feeling of the awareness of
our actions is easily inhibited whenever what we call intellectual
activity proceeds.
Much of the stimulation of our receptor organs is of this generally
occurring nature, and we are not aware of it although the stimuli
received are such as to induce useful and purposeful bodily activity.
In walking along the street we automatically avoid the people, and the
other obstacles that we encounter, by means of regulated movements of
the body and limbs, but this is activity that has become so habitual
and easy that we are hardly aware of it, and not at all, perhaps,
of the physical stimuli which induce it. But not only do we receive
stimuli which are reflected into bodily actions without our being
keenly aware of this reception, but we also receive stimuli which do
not become reflected into bodily activity. It is, Bergson suggests, as
if we were to look out into the street through a sheet of glass held
perpendicularly to our line of sight; held in this way we see perfectly
all that happens in front of us, but when we incline the glass at a
certain angle it becomes a perfect reflector and throws back again the
rays of light that it receives. This is, of course, a physical analogy,
and no comparison of material things with psychical processes can go
very far, but in a way it is more than an analogy. In our indolent
absorbed state of mind we do not as a rule see the objects which we
are not compelled to avoid, and which do not, in any way, influence
our immediate condition of bodily activity. The optical images of all
these things are thrown upon our retinas and are, in some way, thrown
or projected upon the central ganglia, but there the series of events
comes to an end, for the images are not reflected out towards the
periphery of the body as muscular actions. We cannot doubt that this is
why we do not perceive all the stimulation of our organs of sense that
we are sure that take place. These stimuli pass through us, as it were,
unless they are reflected out again as actions. In this reflection, or
translation of neutral into muscular activity, perceptions arise.
But even then perception need not arise. It does not, as a rule,
accompany the automatically performed reflex action, because the latter
is the result of intra-cerebral activities that have become so habitual
that they proceed _without friction_. There are innumerable paths in
the brain along which impulses from the receptor organs may pass into
the motor ganglia, but in the habitually performed reflex actions these
paths have been worn smooth, so to speak. The images of objects which
are perceived over and over again by the receptor organs glide easily
through the brain and as easily translate themselves into muscular,
or some other kind of activity. The things that matter in the life of
an animal which lives “according to nature” are cyclically recurrent
events in which, after a time, there is nothing new. Most of them
proceed just as well in the animal deprived of its cerebral hemispheres
by operation as in the intact cerebrate animal. In the performance of
actions of this kind the organism becomes very much of an automaton.
Let something unusual happen in the street while we are walking
through it--a runaway horse, or the fall of an overhead “live”
wire, for instance, something that has seldom or never formed part
of our experience, and something that may have an immediate effect
on us as living organisms. Then perception arises at once because
the stimulation of our organs of sense presents us with something
which is unfamiliar, and yet not so unfamiliar that it does not
recall from memory, or from derived experience, reminiscences of
the images of somewhat similar things, and of the effects of these.
The train of events that now proceeds in our central nervous system
becomes radically different from that which proceeded in our former,
rather aimless, series of actions. The stimuli no longer pass easily
through the “lower” ganglia of the brain, but flash upwards into the
cortical regions, where they become confronted with the possibility of
innumerable alternative paths and connections with all the parts of
the body. They waver, so to speak, before adopting one or other, or
a combination of these paths; there is hesitation, deliberation, and
finally choice of a path, with the result that a series of muscular
organs become inervated and motor actions, of a type more or less
competent to the situation in which we find ourselves, are set up. In
this hesitation and deliberation perception arises. It is when the
animal may act in a certain way as the result of a stimulus which is
not a continually recurrent one, but at the same time may refrain from
acting, or may act in one of several different ways, that perception of
external things and their relations arises.
That is to say, we perceive and think because we act. We do not look
out on the environment in which we are placed in a speculative kind
of way, merely receiving the images of things, and classifying and
remembering them, while all the time we are passive in so far as our
bodily activities are concerned. If the results of modern physiology
teach us anything in an unequivocal way they teach us this--that the
organs of activity, muscles, glands, and so on, and the organs of sense
and communication, are integrally one series of parts, and that apart
from motor activity nervous activity is an aimless kind of thing. It
is because we act that we think and disentangle the images of things
presented to us by our organs of sense, and subject all that is in the
stream of consciousness to conceptual analysis.[1]
[1] All this is, of course, the argument of Bergson’s earlier books,
_Matière et Mémoire_ and _Données immédiates de la Conscience_.
That is to say, in thinking about the flux of consciousness we
decompose it into what we regard as its constituent parts, and we
confer upon these parts separate existence in space and time. But it
is clear that none of the things which we thus regard as the elements
of our consciousness has any real existence apart from the others. The
smell of the flowers and that of the burnt oil interpenetrate in our
consciousness of the stimulation of our olfactory organs just as do the
jingle of the cab bells, the music of the orchestra, and the throb of
the motor car in the impressions transmitted by our auditory organs.
It is difficult to see that all these things, with the multitude of
other things which we perceive, constitute a “multiplicity in unity,”
that is an assemblage of things which are separate things, but which do
not lie alongside each other in space and mutually exclude each other,
but which are all jammed into each other, so to speak. It is easy to
see that we are conscious of a heterogeneity, and whenever we think of
this multitude of things it seems natural that we should separate them
from each other. The stream of our consciousness is so complex that we
cannot attend to it all at once, not even to the few things that we
have picked out in our example. If we concentrate our attention on any
part, or rather aspect of it, all the rest ceases to exist, or rather
we agree to ignore it, and this very concentration of thought upon one
part of our experience isolates it from all the rest. To a certain
extent the analysis of the complex of sensation is the result of the
work of different receptor organs; certain fields of energy, which we
call light, radiation, etc., affect the nerve-endings in the retina;
chemically active particles in the atmosphere affect the nerve-endings
in the olfactory membranes; and rapidly repeated changes of pressure
in the atmosphere (sound vibrations) affect the auditory organs in the
internal ear, and so on. But this reception of different stimuli by
different receptor organs exists only in the higher animal; there are
no specialised sense organs in a _Paramœcium_, for instance, and the
whole periphery of the animal must receive all these different kinds
of external stimuli at once. The specialisation of its receptor organs
in the higher animal is rather the means whereby the organism becomes
more receptive of its environment, than the means whereby it analyses
that environment. This analysis is the work of the consciousness of the
animal.
[Illustration: FIG. 1.]
Suppose that we draw a curve _AB_ freehand with a single undivided
sweep of the pencil. By making a certain assumption--that the curve
which we drew was one that might be regarded as cyclical, that is,
might be repeated over and over again--we can subject it to harmonic
analysis. We can decompose it into a number of other curves (_CD_,
_EF_, etc.), each of which is a separate “wave” rising above and
falling below the axis _OX_ in a symmetrical manner. If we draw any
vertical line _MN_ cutting these curves, we shall find that the
distance between the axis _OX_ and the main curve _AB_ is always
equal to the algebraic sum of the distances between the axis and the
other curves. These latter we call the harmonic constituents of the
curve _AB_, supposing them to “add up” so as to form it. But _AB_
was something quite simple and elemental and its constituents cannot
be said to have existed in it when we drew it freehand; it was only
by an artifice of practical utility in mathematical computations
that we _constructed_ them. It may be, of course, that the harmonic
constituents of a curve had actual existence apart from the curve
itself, but, in the case that we take, they certainly had not. Now
we must think of our stream of consciousness in much the same way.
It is something immediately experienced and elementary; it is the
concomitant, if we choose so to regard it, of the external processes
that go on outside our bodies. We can investigate it by thinking about
it, and attending to one aspect of it after another, thus arbitrarily
detaching one “part” of it from all the rest, but immediately we
do this we rise above the flux of experience into the region of
intellectual concepts. We have converted a multiplicity of states of
consciousness, all of which co-exist along with each other, and in
each other, and which have no spatial existence, into a multiplicity
of states, visual, auditory, olfactory, etc., which have become
separated from each other and have therefore acquired extension. This
dissociation of the flux of experience is the process of conceptual
analysis carried out by thought.
If we dissociate the stream of consciousness in this way, breaking it
up into states which we choose to regard as separate from each other,
we shall see that of the elements which we thus isolate many are
like each other and can be associated. Obviously there is a greater
resemblance between different smells than between smells and sounds.
Different musical sounds are more like each other than are sounds, and
feelings of heat and cold. There is a greater likeness between the
states of consciousness which arise from the stimulation of the same
receptor organ, than between those that arise from the stimulation
of different receptors. Those differences of sensation accompanying
the stimulation of different sense organs we regard as different in
kind; there is absolutely no resemblance between a colour and a sound,
we say, however much the modern annotator of concert programmes may
suggest the analogy. But we say that there may be different degrees of
stimulation of the same sense organ, and that the sensations that we
thus receive are of the same kind though they differ in intensity. The
whistle of a railway engine becomes louder as the train approaches,
that is to say, more intense, and if we study the physical conditions
that are concomitant with the stimulation of our tympanic membranes
we shall see that waves of alternate rarefaction and compression are
set up in the atmosphere outside our ears. All the time that the train
approaches the frequency of these waves remains the same, that is, just
as many occur in a second when the train is distant as when it is near.
But the amplitude of the waves has been increasing, and the velocity
with which the molecules of air strike against the tympanic membranes
becomes greater the nearer is the source of sound. We can represent
this by means of a diagram which shows that the amplitude of the
waves--which represents the loudness of the sound--increases while the
frequency--which represents the pitch--remains the same. The amplitude
is represented by the straight vertical lines, 11, 22, 33, etc.,
which are of increasing magnitude. Thus we represent the physical
cause of the increasing loudness of the sound by space-magnitudes,
and then we transfer these magnitudes to the states of consciousness
concomitant with the vibrating molecules of air. Suppose that we knew
nothing at all about the cause of the differences of pitch of musical
sounds and that we listen to the notes of the octave, C, D, E,----C,
sounded by an organ; all that we should experience would be that the
sounds were different. If we were to sing the notes we might attain
the intuition that the notes G, A, B were “higher” than the notes C,
D, E, because a greater effort was required in order to produce these
sounds, but obviously this is a different thing from saying that the
notes themselves were “higher” or “lower.” But let us match the notes
by striking tuning-forks, and then having selected forks which give the
notes of the octave let us fix them so that they will make a tracing,
while still vibrating, on a revolving strip of paper. We shall then
find that the fork emitting the note C makes (say) 256 vibrations per
second, the fork D 9/8 256 vibrations, the fork E 5/4 256 vibrations,
and so on. Thus we associate the notes of the octave together and we
say that their quality was the same but that their pitch differed,
and since the pitch depends on the frequency of vibration of the
fork, or of the air in its vicinity, we say that pitch differences are
quantitative ones, and that the states of consciousness which accompany
these physical events are also quantitatively different.
[Illustration: FIG. 2.]
So also with colour. If we had no such apparatus as prisms or
diffraction gratings, which enable us to find what is the wave length
of light, should we have any idea of the spectral hues, red, yellow,
orange, green, etc., as differing from each other quantitatively? It is
certain that we should not. But observation and experiment have shown
that the nerve-endings of the optic nerve in the retina are stimulated
by vibrations of something which we agree to call the ether of space,
and that the frequency of vibration of light which we call red is
less than that which we call orange, while the frequency of vibration
of orange light is less again than that of blue light, and so on. To
our consciousness red, orange, yellow, and blue light are absolutely
different, but we disregard this intuition and we say that our
perceptions of light are similar in kind but differ, in some of them
are more intense than are some others. Again, have we any intuitive
knowledge of increasing temperature? If we dip our hands into ice-cold
water the sensation is one of pain, if the water has a temperature
of 5° C. it feels cold, if it is at 15° C. we have no particular
appreciation of temperature, if at 25° C. it feels very warm, if it
is at 60° it is very hot, and if it is at 90° we are probably scalded
and the feeling is again one of pain. If we place a thermometer in
the water we notice that each sensation in turn is associated with a
progressive lengthening of the mercury thread, and if we investigate
the physical condition of the water we find that at each stage the
velocity of movement of the molecules was greater than that at the
preceding stage. We say, then, that our different perceptions were
those of heat of different degrees of intensity, so transferring to
the perceptions themselves the notions of space-magnitudes acquired by
a study of the expansion of the mercury in the thermometer, or by the
adoption of the physical theory of the kinetic structure of the water.
Yet it is quite certain that what we experienced were quite different
things or conditions, cold, warmth, heat, and pain, and indeed, in this
series of perceptions different receptor organs are involved.
Suppose we listen to the note emitted by a syren which is sounding with
slowly increasing loudness but with a pitch which remains constant. We
do not notice at first that the sound is becoming louder, but after a
little time we do notice a difference. Let us call the amplitude of
vibration of the air when the syren first sounds _E_, and then, when we
notice a difference, let us call the amplitude Δ_E_ + _E_, Δ_E_ being
the increment of amplitude. Let us call our sensation when the syren
first sounds _S_, and our sensations when the sound has become louder
_S_ + Δ_S_, Δ_S_ being the “increment of sensation.” Then the relation
holds:--
Δ_E_/_E_ = constant.
That is to say, the louder is the sound the greater must be the
increase of loudness before we notice a difference. Let us assume now
that the successive sensations of loudness that we receive as the syren
blows louder and louder are, each of them, just the same amount louder
than the preceding sound; that is to say, let us assume that what we
experience are “minimal perceptible differences” of sensation--that
they are “elements of loudness”--thus we construct a series of sounds
each of which differs from that preceding it by an elemental increment
of loudness. Now things that cannot be further decomposed are
necessarily equal to each other; if, for instance, the atoms represent
the ultimate units into which we break up the matter called oxygen,
then these atoms are all equal to each other. Therefore the increments
of loudness are equal to each other.
[Illustration: FIG. 3.]
If we plot these equal increments of loudness as the dependent variable
_S_ in a graph, and the amplitude of the vibrations of the atmosphere
as the independent variable _E_, we can obtain the following curve.
If we investigate this we shall find that a certain relation exists
between the “values” of the sensation and the values of the stimuli
that correspond to them; a regular increase in the loudness of the
sensation corresponds to a regular increase in the logarithms of the
strength of the stimuli. Let S = the sensation, _E_ the stimulus, and
_C_ and _Q_ constants; then
_S_ = _C_ log(_E_/_Q_);
so that we seem to establish a mathematical relation between the
intensity of our sensations and the intensity of the stimuli that give
rise to those sensations, but this relation depends on the assumption
that what we call “minimal perceptible differences” of sensation are
numerical differences that are equal to each other, and this is, of
course, an assumption that cannot possibly be proved.
Thus we decompose our stream of consciousness into a series of
quantitatively different and qualitatively different things, upon
each of which we confer independent existence. We attribute to these
different aspects of our consciousness extension, but the extension is
due only to our analysis; for the qualities of pitch, loudness, colour,
odour, etc., which we disentangle from each other, did not exist apart
from each other, any more than do the sine and cosine curves into which
we decompose an arbitrarily drawn curved line. The multiplicity of
our consciousness is intensive, like the multiplicity that we see to
exist in the abstract number ten. This number stands for a group of
things, but its multiplicity is intensive and only exists because we
are able to subdivide anything in thought to an indefinite extent. Now,
so far we have only separated what we agree to regard as the elemental
parts of our general perception of the environment, but it is to be
noted that we have not given to these elements anything like spatial
extension.
We may, if we like, regard our intuition of space as that of an
indefinitely large, homogeneous, empty medium which surrounds us and
in which we may, in imagination, place things. So regarded it is
difficult to see in what way our notion of space differs from our idea
of “nothing,” a pseudo-idea incapable of analysis, except into the
idea of something which might be somewhere else. The more we think
about it the more we shall become convinced that space, that is the
“form” of space, represents our actual or potential modes of motion,
that is, our powers of exertional activity. Space, we say, has three
dimensions; in all our analysis of the universe, and of the activities
that we can perceive in it, this idea of movement in three dimensions,
forward and backward, up and down, and right and left, occurs; and
we have to recognise that in it there is something fundamental, as
fundamental as the intuitive knowledge that we possess of the direction
of right and left. It is because we can move in such a way that any
of our motions, no matter how complex, can be resolved into the
components of backward and forward, right and left, and up and down,
these directions all being at right angles to each other, that we speak
of our movements as three-dimensional ones. Our geometry is founded,
therefore, on concepts derived from our modes of activity; and there is
nothing in the universe, apart from our own activity, that makes this
the only geometry possible to us. Euclidean geometry does not depend
on the constitution of the external universe, but on the nature of the
organism itself.
There is a little Infusorian which lives, in its adult phase, on the
surface of the spherical ova of fishes. These ova float freely in
sea water, and the Infusorian crawls on their surfaces, moving about
by means of ciliary appendages. It does not swim about in the water,
but adheres closely to the surface of the ovum on which it lives. Let
us suppose that it is an intelligent animal and that it is able to
construct a geometry of its own; if so, this geometry would be very
different from our own.
It would be a two-dimensional geometry, for the animal can move
backward and forward, and right and left, but not up and down; it
is a stereotropic organism, as Jacques Loeb would say, that is, it
is _compelled_ by its organisation to apply its body closely to the
surface on which it lives. But its two-dimensional geometry would, on
this account, be different from ours. Our straight lines are really the
_directions_ in which we move from one point to another point in such
a way as to involve the least exertion; they are the shortest distances
between two points, and if we deviate from them we exert a greater
degree of activity than if we had moved along them. For us there is
only one straight line that can be drawn between two points, but this
is not necessarily true for our Infusorian, and its straight line need
not be the shortest distance between two points. It might be either the
longest or the shortest distance between the points, for the latter can
always be placed on a great circle passing through the two points and
the poles of the egg, and in moving from a point on which it is placed
the animal could reach the other point by moving in two directions,
just as we could go round the earth along the equator by moving to the
east or to the west. Therefore the straight line of the Infusorian
would be not only a scalar quantity but a vector quantity, that is,
it would represent, not only a quantity of energy, but a quantity of
energy that has direction. For us only one straight line can be drawn
between two given points, but this limitation would not exist in the
two-dimensional geometry of a curved surface. Suppose that the two
points are situated on a great circle and that they are exactly 180°
apart; then the Infusorian could move from one pole to another pole
along an infinite number of straight lines or meridians all of which
had a different direction, but all of which were of the same length;
that is to say, in this geometry an infinite number of straight lines
can be drawn between the same two points. Again, its triangles _might_
be different from ours; our triangles are figures formed by drawing
straight lines between three points, and on a plane surface the sum
of the angles of the triangle are together equal to two right angles,
though on a curved surface they may be greater or less than two right
angles. But our Infusorian could not imagine a triangle in which the
sum of the angles was not greater than two right angles, for all its
figures would be drawn on a convex surface.
Our three-dimensional geometry depends, therefore, on our modes of
activity and the concepts with which it operates; points, straight
lines, etc. are conceptual limits to those modes of activity. We can
imagine a straight line only as a direction along which we can move
without deviating to the right or the left, or up or down. But even
if we draw such a line on paper with a fine pencil the trace would
still have some width, and we can imagine ourselves small enough to be
able to deviate to the right or the left within the width of the line
drawn on the paper. We might make a very small mark on the paper, but
no matter how small this mark is it would still have some magnitude;
otherwise we should be unable to see it. If the straight line had
no width and the point no magnitude they would have no perceptual
existence. Our perceptual triangles are not figures, the angles of
which are necessarily equal to two right angles. If we drive three
walking sticks into a field and then measure the angles between them by
means of a sextant we shall find that the sum is _nearly_ 180°, but in
general not that amount. If we stick a darning needle into the heads
of each of the walking sticks and then remeasure the angles by means
of a theodolite we shall obtain values which are nearer to that of two
right angles, but we should not, except by “accident,” obtain exactly
this value. We do not, therefore, get the “theoretical” result, and we
say this is because of the errors of our methods of observation; but
why do we suppose that there is such a theoretical result from which
our observations deviate, if our observations themselves do not in
general give this ideal result? We might accumulate a great series
of measurements of the angles of our triangle, and we should then
find that these results would tend to group themselves symmetrically
round a certain value which would be 180°. Some of the results would
be considerably less than the ideal, and some of them would be
considerably more; but these relatively great deviations would be small
in number and most of the results would be a very little less than 180°
or a very little more, and there would be as many which would be a
little less as those that were a little more. We should have formed a
“frequency distribution”[2] with its “mode” at 180°.
[2] See appendix, p. 350.
But by “reasoning” about the “properties” of these lines and triangles
in plane two-dimensional space, we should arrive at the conclusion
that the angles of a triangle were equal to 180°, and neither more nor
less. We should then think of a straight line as still a _path_ along
which we move in imagination, and a path which still has some width.
But we imagine the width of the path to become less and less, so that,
even if we imagine ourselves to become thinner and thinner, we should
be unable to deviate either to the right or left in moving along the
path, because the thinner we make ourselves the thinner becomes also
the path. We imagine our intuition of a deviation to the right or left
becoming keener and keener, so that, no matter how small the deviation
we should still be able to appreciate it by the extra exertion which
it would involve. We think of a point as a little spot, and we think
of ourselves as being very small indeed, so that we can move about on
this spot. But we can reduce the area of the spot more and more, until
it becomes “infinitesimally” small; and at the same time we think of
ourselves as becoming smaller and smaller, so that we can still move
about on the spot. But we think of the area of the spot as becoming so
small that no matter how small we make ourselves we are unable to move
on it.
This means that we substitute conceptual lines and points and triangles
for the perceptual ones of our experience, and then we operate in
imagination with these concepts. That is to say, we carry our modes
of exertional activity to their _limits_,[3] in the way which we have
tried to indicate above--a process of thought which is the foundation
of the reasoning of the infinitesimal calculus.
[3] See appendix, p. 346.
What we call space, therefore, depends on our intuition of bodily
exertion. This intuition includes the knowledge that a certain change
has occurred as the consequence of the expenditure of a certain amount
of bodily energy, and that, as the result of this change, the relation
of the rest of the universe to our body has become different. We think
of our body as the origin, or centre, of a system of co-ordinates:--
[Illustration: FIG. 4.]
We imagine three lines at right angles to each other to extend
indefinitely out into space, and we think of ourselves as being
situated at the point of intersection of these three straight lines.
If anything moves in the universe outside ourselves we can resolve
this motion into three components, each of which is to be measured
along one of the axes of our system of co-ordinates. But any motion
whatever in the universe outside ourselves can be represented equally
well by supposing that the origin of the system of co-ordinates has
been changed; that is, by supposing that we have changed our position
relative to the rest of the universe. Therefore motion outside
ourselves is not to be distinguished from a contrary motion of our own
body--a statement of the “principle of relativity”--except that any
change outside ourselves may be distinguished from that compensatory
change in the position of our body which _appears_ to be the same
thing, by the absence of the intuition that we have expended a certain
quantity of energy in producing the change. Conscious motion of our own
body is something _absolute_; all other motion is relative.
So far we have been speaking of our crude bodily motion, but a very
little consideration will show that our knowledge of space attained
by scientific measurements depends just as much on our intuition of
our bodily activity, and its direction; the measurement of a stellar
parallax, or that of the meridian altitude of the sun, for instance,
by astronomical instruments, involves bodily exertion, though of a
refined kind. Three-dimensional space, that is _our_ space, therefore
represents the manner of our activity, just as convex two-dimensional
space represents the manner of the activity of the Infusorian, and
one-dimensional space would represent the manner of activity of an
animal which was compelled to live in a tube, the sides of which
it fitted closely, so that it could move only in one direction--up
and down. A parasite, living attached to some fixed object, and
the movements of which were represented only by the growth of its
tissues, could not form any idea of space; and the “higher” forms of
geometry, that is, space of four or more dimensions, present no clear
notion to our minds, even although we regard the operations included
in mathematics of this kind as pure symbolism, because we cannot
relate this imaginary space to any form of bodily exertion. Geometry,
then, represents the manner in which our bodily exertion cuts up the
homogeneous medium in which we live.
Motion, whether it be that of our own body in controlled muscular
activity, or that imaginary motion of the environment which we
call giddiness, or a sensibly perceived motion of some part of the
environment, that is, a motion which we can compensate by some actual
or imaginary change in the position of our own body produced by our
own exertion, is an intuitively felt change, and is incapable of
intellectual representation. It is not clearly conceived either in
ancient or in modern geometry. Euclidean geometry is, as we have
seen, based directly on our intuition of bodily exertion, but it is
essentially static in treatment. Let it be admitted that we can draw a
straight line of any length and in any direction, and so on; then we
regard these straight lines, etc., as motionless, abstract things, and
we proceed to discuss their relationships. Cartesian geometry, and the
methods of the infinitesimal calculus, do not treat of real motion, and
the concept, if it is introduced at all, is introduced illegitimately
and surreptitiously. Consider what we do when we “plot a curve.” Let
the latter be a parabola having the equation _y_ = 1/2 _x_. Now a
parabola is defined as “the locus of a point which _moves_, so that its
distance from a fixed point is in a constant relation to its distance
from a fixed straight line.” How do we construct such a curve?
[Illustration: FIG. 5.]
We proceed to fix the positions of a series of points in this way:
there are two straight lines, _OX_ and _OY_, at right angles to each
other, and we measure off certain steps along the line _OX_; these
steps are _OX_↓{0·5}, _OX_↓{1}, _OX_↓{1·5}, _OX_↓{2}, and so on, the
small numerals indicating the distance of each point (_OX_↓{0·5}, etc.)
from the origin _O_. We then draw lines perpendicular to the _X_-axis
through these points. We have now to calculate one-half of the square
of each of these lengths _OX_↓{0·5}, _OX_↓{1}, etc., and then we mark
off these calculated lengths along the perpendicular lines. The point
_A_, for instance, is 1/2(0·5)^2 from the point _X_↓{0·5}, _B_ is
1/2(1)^2 from _X_↓{1}, and so on. In this way we obtain a series of
points, _A_, _B_, _C_, _D_, _E_, etc., and these are points on the
locus of the “moving” point.
[Illustration: FIG. 6.]
There is nothing at all about motion here. All that we have done is
to measure lengths. We have made a kind of counterpoint, _X_-points
against _Y_-points, but we have not even made a curve. We connect the
points _A_, _B_, _C_, _D_, _E_, etc., by means of short, straight
lines, and then we may connect together these short lines, and, if we
plot a number of intermediate points between those that we have already
obtained and join these, the points may be so close together that they
may seem to be indistinguishable from a curve. Yet, no matter how
numerous they may be, they can never be connected together so as to
form a curve; we therefore draw a curved line freehand through them,
and at once, in so doing, we abandon our intellectual methods, for our
curve depends on our intuition of _continuously changing direction_.
But if we think about it we shall find that we can form no clear
intellectual notion of continuity and we can only measure the curvature
of a line _at a point in_ the line by drawing a tangent to the curve at
this point, and then by measuring the slope of the tangent. The curve
itself we obviously leave out of consideration.
We cannot conceive of the point moving along the locus _OD_. We can
think of it only as _at_ the places _O_, _A_, _B_, _C_, _D_, _E_, etc.,
but we must neglect the intervals _OA_, _AB_, _BC_, _CD_, _DE_, and so
on, or we can divide them into smaller intervals by supposing the point
to have occupied the positions _f_, _g_, _i_, _j_, between the points
_A_ and _B_, for instance. Yet, no matter how many these intervals
may be, we can only think of the point as being _at_ the places _O_,
_A_, _B_, _C_, _D_, _E_, or at _f_, _g_, _i_, _j_, and so on. We never
think of the intervals themselves, and, if all we think about is the
_position_ of the point, we do not really think of it as in motion at
all. We can _see_ it in motion, but we cannot form an intellectual
concept of its motion. It is not really necessary that we should in the
affairs of everyday life, but for the adequate treatment of problems
involving rates of change science had to wait for the invention of the
methods of the infinitesimal calculus before this disability of the
human mind could be circumvented.
But the moving point occupies _successively_ a number of different
positions in space. If it is a material point that we observe to move
from one place to another, we perceive that a certain interval of our
duration corresponds with the change of position of the point. Duration
was not used up in the occupancy of the different positions _O_, _A_,
_B_, _C_, _D_, _E_, and so on, nor in that of the occupancy of the
indefinitely numerous other positions in which we may place the moving
point, but in the intervals themselves. We have said “duration” and
not “time,” using Bergson’s term. By duration and time we understand
different things.
Time is, for us, only a series of standard events which punctuate, so
to speak, our experienced duration. The unit of time is the sidereal
day, that is, the interval of time between two successive transits
of a fixed star across the arbitrary meridian. But if we try to
conceptualise this interval we find that we can do so only by breaking
it up into smaller intervals, and this we do by using a pendulum of a
certain length which makes a certain number of swings (86,400) during
the interval between the two transits of the star. Thus we obtain a
smaller interval of duration and we call this a second of time. But for
many purposes this interval is too long, and we can again sub-divide
it by making use of a tuning-fork which makes, say, 1000 complete
vibrations in a second; in this way we obtain still smaller intervals
of duration--the sigmata of the physiologists. A sigma, therefore,
represents the interval between the beginning and end of one complete
vibration of a certain kind of tuning-fork; a second, that between the
beginning and end of one complete swing of a pendulum of a certain
length, placed at certain parts of the earth’s surface; and a day,
that between two successive transits of a fixed star across a selected
meridian, after all the necessary corrections have been made to the
observation. These actual occurrences, the positions of the prongs
of the tuning-fork, or those of the bob of the pendulum, or those of
the fixed star do not involve duration. We consider the meridian of
Greenwich as an imaginary line drawn across the celestial sphere, and
the star as a point of light, so that the actual transit is, in the
limit, an occurrence which occupies only an “infinitesimal” interval of
duration. So also with the pendulum and the tuning-fork; the positions
of these things do not “use up” time, and even if the intervals into
which we divide astronomical time are indefinitely numerous no real
quantity of duration is taken up by their occurrence. We know that the
interval between two successive transits of a fixed star are not really
constant, that is, the astronomical day is lengthening by an incredibly
small part of a second each year, but how do we know this? It is
not that we can _feel_ the increments of duration, but just that we
assume that Newton’s laws of motion are true; and hence that the tidal
friction due to the motions of the earth, sun, and moon must retard
the period of rotation of the earth so that the intervals between two
successive transits of a star must become greater.
Thus we do not conceptualise the actual intervals of duration of which
we are able to mark the end-points; they are lived by us, and they are
real absolute things independent of our wills. Suppose we come in from
a long walk, tired and thirsty, and ask the maid to get tea ready at
once. She puts the kettle on the gas stove and then sits down to read.
The water takes, say, five minutes to boil. What do we mean by this?
This is what we mean:--
{_The pendulum _and it has _The time
{ of the clock now swung_ _and now_ and so elapses_
Time { has already on
{ swung_
{ M times M + n times M + 2n times P swings
| | | |
{_The water in _it is now _and now_ _the kettle
{ the kettle at_ and so boils_
{ is at_ on
{ T° T° + t° T° + 2t° 100°
Tempera- { | | | |
ture {_The volume _it is now_ _and now_ It is
{ of mercury in | | and so |
{ the thermo- | | on |
{ meter is_ | | |
{ V V + v V + 2v W
What we call time here is only a series of simultaneously occurring
events. The standard events are the positions of the hands of the
clock on the clock face, that is, lengths of arc recording the number
of swings of the pendulum that have occurred since the beginning of
the operation of the boiling of the kettle. When this began, the hands
of the clock were at, say, 4.30, and the temperature of the water
was then, say, 17° C.; and, when it ended, the hands of the clock
were at 4.35 and the temperature of the water was 100° C. It is only
the simultaneities of these events that we have recorded and not the
interval of duration that they mark. It does not matter how many times
we might have looked at the hands of the clock and the thermometer, we
should still have observed only simultaneities.
But we had to _wait_ for the kettle to boil, and the temperature 100°
was attained _after_ the temperature 90°, and so on. What does this
mean? While we were waiting, the water seemed to take an intolerably
long time to boil. But the maid was reading one of Mr Charles Garvice’s
novels, and “before she knew where she was” the kettle boiled over.
There was a certain interval of duration experienced by her, and
another, but different, interval of duration experienced by us. In each
case there was a stream of consciousness. We felt fatigue, thirst, a
lack of satisfaction, wandering attention, and irritation--all that
was our duration. But the maid was identifying herself with Lady Mary,
who had sprained an ankle and was being helped along by the new, young
gamekeeper, and that was her duration.
There need not be any succession of events in the conceptual
representation of a physical process. There is, for instance, no
succession in such a conception as is represented by the following
diagram--a conception well worth analysis:--
[Illustration: FIG. 7.]
The figure represents a tracing made by a muscle-nerve preparation.
A living muscle taken from an animal has been attached to a light
lever, the end of which makes a scratch on a piece of smoked paper.
The paper is fastened on a revolving cylinder and so long as the
muscle is motionless the end of the lever marks a horizontal line on
the paper. But if the muscle is stimulated so that it contracts and
then relaxes again the lever is pulled up and is then lowered, and so
its point makes a curve on the paper. The nerve going to the muscle
can be stimulated electrically and the moment of the stimulation can
be recorded by another lever, which makes a mark on the paper below
the trace made by the lever which is attached to the muscle. Two
such shocks have been applied to the nerve and they have elicited
two contractions of the muscle and these two contractions have fused
together.
In the actual experiment the operators could _see_ that the muscle
moved, and they could _feel_ that a certain interval of their own
duration coincided with the interval between the first and second
depressions of the key that made the electric shocks. But the extent
of motion of the muscle was too small, and the depressions of the key
succeeded each other too rapidly to be easily observed, and therefore
all these events were made to record themselves on the myogram. The
series of little notches at the base of the figure represent the
movements of the time-lever, that is, they are scratches made on
the paper by a little lever which moves up and down at a rate fixed
beforehand. Now when this time lever had made ten notches on the paper
the first shock was applied to the nerve, and at the eleventh the
muscle began to contract. At the seventeenth notch the second shock
was applied and the muscle continued to contract. At the twenty-fifth
notch the muscle ceased to contract and began to relax, and at the
forty-second notch the muscle had ceased to contract. Everything now
becomes clear and easy to represent mentally; the time-lever makes 100
notches on the paper in a second, so that there was an interval of
0.07 seconds between the two stimuli, and these two stimuli produced a
compound contraction of the muscle lasting for 0.1 second. This is what
the experimenters might have perceived, had human unaided senses been
sufficiently acute. But they are not, and so the crude perception of
the results of the experiment is replaced by a conception of the train
of events involved in the operation. Duration and succession disappear
and the myogram represents only a series of simultaneous events of
this nature; the first stimulus occurs simultaneously with the tenth
movement of the time-lever; the second stimulus with the seventeenth,
and so on. In seeing the experiment the operators had to _wait_ for one
phase to be completed before they could observe another one, but in
reasoning about it all the phases are spread out and are present in the
conception at once. The duration was in the operators but not in the
experiment: it was experienced, but it disappears when the results of
the experiment are conceptualised.
A succession of events is in ourselves and not in the events observed.
If a point is said to move along the locus _OD_ through the positions
_A_, _B_, _C_, it is we that have the feeling of succession, and
the whole trajectory, or locus, or path of the point corresponds
with a portion of our duration. The operation of boiling the kettle
corresponds with a portion of our duration, which in its turn
corresponds with that part of our duration which was marked by the
positions of the hands of the clock. Thus we perceive a simultaneity
in these two trains of events, and this enables us to assign a
certain period of astronomical time to the operation of raising the
temperature of the water, in the conditions of the experiment, from
17° C. to 100° C. But there is nothing absolute in this interval
of astronomical time: what is absolute is that certain successions
of events always correspond with other successions of events. A
certain number of swings of a seconds-pendulum always corresponds
with a certain rise in temperature of a definite mass of water which
is in thermal contact with an indefinitely large reservoir of heat
at a certain temperature, and, no matter how often we repeat this
experience, the same simultaneity is always to be observed. Thus what
the physicist considers is not intervals of his own duration but series
of correspondences--that is, correspondences of certain standard events
with the events which he is studying.
In reality time, in the sense of the astronomer’s time, does not enter
into the methods of the mathematical physicist. Let us suppose that he
is investigating the change that occurs in a material system between
the two moments of time _t_↓{1} and _t_↓{2}, these moments being
separated from each other by a period of duration that we can feel. Let
the system be, say, the earth and moon; the first body being supposed
to be motionless, and the second being supposed to have a certain
tangential velocity of movement. If the interval _t_↓{1} to _t_↓{2}
is really an interval of astronomical time, the problem, what is the
difference of position of the moon owing to the gravitation of the
earth, is incapable of solution, and even if we reduce the interval of
time indefinitely while still supposing that it is a finite interval,
the mathematical difficulty remains. We then replace the finite
interval _t_↓{1} to _t_↓{2} by the differential _dt_, which means
that the two phases of the system, motionless earth and moving moon
at the time _t_↓{1}, and motionless earth and moving moon at the time
_t_↓{2}, are separated by an interval of time _dt_, which is smaller
than any finite interval that we can conceive. We must then integrate
the differential of the position difference so as to obtain the real
difference in the condition of the system after the finite interval
of time _t_↓{1} to _t_↓{2} has elapsed. Thus mathematics, incapable
of dealing with real intervals of time, _evades_ this difficulty by
considering tendencies, not real occurrences.
Things that happen in a part of inorganic nature arbitrarily detached
from the rest, and investigated by the methods of mathematical physics,
do not endure. Let us suppose that we take some silver and add nitric
acid to it: the metal dissolves. We can then add hydrochloric acid
to the solution and precipitate the metal in the form of chloride;
and we can then fuse this chloride with carbonate of soda, or some
other substance, and so obtain the metal again. If we work carefully
enough we can repeat this series of operations again and again and the
original portion of silver will remain unchanged both in nature and
in mass. All the chemical reactions into which it has entered have
not affected it in any way; that is to say, these reactions have not
endured.
If we inject a serum, containing a toxin, into the blood stream of
a susceptible animal, certain things happen. The animal will become
ill, but, provided that the amount of serum which has been injected
was not too great, it will recover. If the toxin be again injected
a reaction occurs, but the animal does not become so ill as on the
first occasion, and after a number of injections the dose administered
may be so great as to kill a susceptible animal but may yet produce
no effect on the animal which is the subject of the process of
immunisation: immunity has been conferred on it. Now can we compare the
two operations, that of the solution and precipitation of the metal
and that of the immunisation of the animal? We can to some extent, but
the analogy soon fails, and indeed we should not attempt to formulate
a theory of immunity on a physico-chemical basis if we did not start
with the assumption that the series of operations was one in which
only physico-chemical reactions were involved, that is to say, there
is nothing in the phenomena of immunisation that suggests that what
occurs in the animal body is similar to what we can cause to occur in
inorganic materials outside the tissues of the living organism. We
start with the assumption that the administration of the toxin causes
the formation of an antitoxin in very much the same sort of way as
the administration of hydrochloric acid to a solution of nitrate of
silver causes the formation of chloride of silver. This antitoxin
then neutralises the dose of toxin which may be administered after
the process of immunisation has been effected, very much in the same
sort of way as a certain amount of some acid can be neutralised by an
equivalent amount of some base with which the acid can combine. If
the reader will analyse any of the theories of immunisation current
at the present day he will find that these are the physical ideas
that are involved in it.[4] But physiological science has the much
more formidable task of explaining the persistence of the immunity.
The animal rendered immune to the toxins produced by certain species
of bacteria may remain so for many years, that is, for a very long
time after the antitoxins originally produced by the reaction of the
tissues to the toxins first administered have disappeared. We must
imagine, therefore, that the anti-substances produced originally
by the reaction of the toxin are produced again and again by the
tissues of the susceptible animal, for the latter may resist repeated
infections, that is, repeated doses of toxin, without illness. But
then the tissues of the animal body are transitory substances and they
do not persist unchanged. Muscles, glands, connective tissues, even
nerve-fibres and nerve-cells undergo metabolism, and the chemical
substances of which they are composed break down into the excretory
products, pass out into the blood stream, and are eliminated from
the body; while at the same time these tissues are continually being
renewed from the nutritive substances in the blood and lymph. It is the
_organisation_ of the tissues--their form and modes of reaction--that
endure, but the material substances of which they are composed are
in a state of continual flux. Yet the organisation of these tissues
does not persist unchanged, for it is continually _responding_ to new
conditions experienced by it. The reactions that occur when a toxin
is administered to a susceptible animal affect the organisation of
its tissues in such a way that the latter acquire the capability of
producing antitoxins which may--if we like to say so--neutralise the
toxins that enter into them when they become infected. The reaction
endures. But this is a different thing from saying that the process is
a physico-chemical one alone.
[4] Except that, of course, the reactions that are supposed to occur
are very complex ones.
This is what we must understand by the duration of the organism.
Everything that it experiences for the first time persists in its
organisation. It acquires the ability of responding to some stimulus
by a definite, purposeful reaction, the effect of which is to aid
it in its struggle for existence; and this reaction, once carried
out, becomes a “motor habit” or the basis of a reflex, or in some
other way, as in the process of immunisation, remains a part of the
modes of functioning of the animal. In our behaviour certain cerebral
nerve tracts become laid down and continue to exist throughout life,
modifying all our future experience. Our past experience accumulates.
There must be direct continuity in our flux of consciousness, for
no perception seems ever to fade absolutely from memory. This
continual addition of perceptions to those that already exist makes
our consciousness ever become more complex, so that a perception
experienced for the first time is never quite the same when it is again
experienced. The first time that we go up and down in an elevator,
or sit on a “joy-wheel,” or ascend in a balloon or an aeroplane, or
become intoxicated, constitutes an unique event in our lives, and we
experience a “new sensation.” What the blasé man of the world complains
of is this accumulation, or rather persistence, of his experiences. A
repetition of the same stimulus never again begets the same perception.
The first hearing of a modern drawing-room song may be enjoyable, but
the next time we hear it we are not interested, and by-and-bye it
becomes very tiresome. The first hearing of a great symphony usually
perplexes us, and we are perhaps repelled by unusual harmonies, or
progressions, or strange modulations, but subsequent hearings afford
increasing pleasure. We say that there was “so much in it” that we
did not understand it, yet precisely the same series of external
stimuli affected our auditory membranes on each occasion, and the same
molecular disturbances were transmitted along our afferent nerves
to the central nervous system, where the same physical effects must
have been produced. The difference in all these cases between the
repetitions of the same stimuli was that the later ones became added
to the earlier ones, so that the state of consciousness produced by,
or which was concomitant with, these external stimuli was a different
state in each case.
This is the duration of the intelligently acting animal: it is not
merely memory, but memory and the accumulation of all its past modes
of responding to changes in its environment, whether these modes of
response were conscious ones (as in the case of an intelligently
performed or “learned” action), or unconscious ones (as, for instance,
in the case of the acquirement of immunity by an animal which had
become able to resist disease). It is not merely the experience of
the individual organism, but also all the experience of those things
which were done or experienced by the ancestry of the organism, and
which were transmitted by heredity to the progeny. Motor habits are
formed, so that much the same series of muscular actions are carried
out when a stimulus formerly experienced is again experienced. Pure
memory remains, so that the images of past things and actions somehow
persist in our consciousness. Physical analogy suggests that these
images are inscribed on the substance of the brain or are stored away
in some manner; but, apart from the incredible difficulty of imagining
a mechanism competent for this purpose, it is obvious that we thus
apply to the investigation of our consciousness (which is an intensive
multiplicity), the concept of extension which can only apply in all
its strictness to the things outside ourselves on which we are able
to act. All these motor habits, functional reactions, and memory
images are our duration or accumulated experience. The motor habits
and those functional habitual reactions of other parts of the body
than the sensori-motor system are the basis of our actions, but the
memory images are, so to speak, pressed back into that part of our
organisation which does not emerge into consciousness. Only so much
of them as bear on the situation in which we, for the moment, find
ourselves and which may therefore influence our actions, flash out
into consciousness. As “dreamers” we indulge ourselves in the luxury
of becoming conscious of these memory images, but as “men of action”
we sternly repress them, or so much of them as do not assist us in the
actions that we are performing. Yet it is in the experience of each of
us that, in spite of this continual inhibition, parts of our memories
slip through the barriers of utility and surreptitiously remind us of
all that we have been and thought.
* * * * *
Thus we simplify the stream of our consciousness. That of which we
are conscious at any time is never more than a part of our crude
sensation: we never perceive more than a small part of all that our
organs of sense transmit to our central nervous system. But even these
chosen perceptions of the external world are so rich, so chaotic and
confused, that we are unable to attend to them all at once and we
therefore “skeletonise” the contents of our consciousness. We think
about it a bit at a time. It is an unitary thing, unable to be broken
up, but we look at it from a great number of different points of view,
so to speak; and then, fixing our attention on some aspect of it, we
agree to ignore all the rest. We thus detach parts of it from the rest
and, having thus arbitrarily decomposed it, we call these separate
aspects the elements of our perceptions, and confer upon them separate
existence in space and time. We remember and classify things and
group together all those that seem to resemble each other. We form
genera, agreeing to ignore all but the most general characteristics of
the things which we try to conceptualise. We do not think separately
about all the dogs or horses or fishes that we have ever seen, but we
group all these animals into species, and it is usually the species
that we think about when the idea of a dog or a horse or a herring
emerges into our consciousness. When we think about a tramcar we do
not think about all the separate vehicles that we have seen, nor
about their colours, nor the advertisements on the boards outside,
nor the people hanging on to the straps inside. Just so much of the
experience of what is relevant to the purpose of our thought enters
into our idea of the tramcar: it is a conceptual vehicle that we
think about. Such is the nature of the concepts that form the basis
of our reasoning: they are generalised aspects of our experience of
nature, usually poorer in content than were the actually perceived
things, except when it is necessary that some individual thing seen
or otherwise experienced should be investigated or reasoned about.
All our descriptions of nature are conceptual schemes. The world of
perception, says William James, is too rich to be attended to all at
once, but in conceptualising it we spread it out and make it thinner,
and we mark out boundaries and division lines in it that do not really
exist. It is this generalised nature that is the subject matter of
our reasoning of pure science; and it is these concepts that form the
matter of all our descriptions. We do not describe nature “as we see
it,” it is our conceptions that we write about. Genera and species
and varieties do not really exist in the animate world: all these are
logical categories generated by our thought, concepts that facilitate
our descriptions. When an anatomist gives an account of the structure
of an animal he does not say what it looks like, nor as a rule does
he content himself by making a photograph of his dissections. For him
the animal is a complex of muscles, skeleton, nerves, glands, and so
on, and in his drawings all these things are given an individuality
that they do not really possess. In the living creature there were no
such sharply-distinguished organs as a good drawing represents: all
are bound together and are continuous. But for practical convenience
in description--that is, in the long run, that we may act upon these
things, we isolate from each other aspects that are in reality one
unitary whole.
* * * * *
The universe, that is, all that is given to us, presents itself
as immediately perceived phenomena which are then conceptually
transformed. It is an aggregate of things--gross matter, particles,
molecules, atoms, and electrons. These things have separate existence
and shape, so that each of them lies outside all other things--we apply
to them the category of extension. They possess properties--that is,
they are hard, or heavy, or hot, or cold, or they are coloured, or they
smell, and so on--we thus apply to them the category of inherence. They
are not things that are immutable, for they change in place, or are
transformed in other ways, that is, they are acted upon by energies.
But beneath the properties of the things, or the transformations that
they undergo, we imagine something that has properties and which
transforms: it is not convenient that we speak solely of attributes or
transformations as entities in themselves, for we think of things as
having properties and being subject to transformations. Thus we apply
the category of substance.
Has this universe that we construct from the data of sensation
objective reality? We are led quite naturally by our study of
physiology to the notion of idealism. We see that our perception
of things, that is, our knowledge of the universe, depends on the
integrity of functioning of certain bodily structures, and upon the
condition that in men in general this integrity of functioning is
normal, that is, common to the great majority of mankind.
To say that a thing exists is to say that it is perceived in some way;
that immediately or remotely it affects our state of consciousness.
To say that the star Sirius exists is to say that the stimulation
of the retina by a minute spot of light transmits certain molecular
disturbances along the optic nerve, and that other molecular
disturbances are set up in the tissues of the central nervous system.
Even if we do not see those dark stars that we know to exist, there are
still evidences of their being that in some way affect the instruments
of the astronomer and lead to their being perceived. Even if we do
not actually see the emanations from a radio-active substance, we can
cause these emanations to produce changes in something that we can
see. We speak of the star as a minute spot of coloured light. But if
we are short-sighted the spot becomes a little flare, and if we are
colour-blind the hue of the star is different from what it is to normal
persons. If we put a drop of atropine into one eye and then close the
other, objects appear to lose their distinctness, but if we close
this eye and then open the other, the original sharpness of vision
returns. When we are bilious, wisps and spots may appear on a sheet
of white paper that at other times was blank. If we take an overdose
of quinine, rustlings and singing noises become apparent even in
conditions that ought to preclude all sensation of sound. If we have
a bad cold, we do not smell substances which at other times strongly
affect our olfactory membranes. When we become intoxicated, a host of
aberrations of sense displace our normal perceptions of things.
Our perception of the universe, therefore, depends on the normal
functioning of our organs of sense, that is, such modes of functioning
as we can describe and communicate to others, and which are thus
common to the majority of other men and women. These perceptions
resulting from the normal functioning of the organs of sense constitute
givenness, and we enlarge, or conceptualise this givenness and call it
the subject matter of science. But what is this reality that we say
is external to us? It is, we see, our inner consciousness. If we walk
along a road in the dark we can feel what is the nature of the path on
which we tread, whether stones or gravel, or sand or grass. But this
feeling is obviously not in the soles of our boots, and neither is it
in the skin of the feet, for we should feel nothing if the afferent
nerves in the legs were severed. Is it then in the brain? It would
appear to be there, but it disappears if certain tracts in the brain
are injured.
All that we can say is that the appearance of reality of things outside
ourselves is only the ever-changing condition of our consciousness.
This is all that we immediately know, and if we say that there is an
universe external to ourselves we thus project outside our own minds
what is in them; and we construct an environment which may or may not
exist, but which we have no right to say does exist. A philosophy based
on the science of the organism would appear to be restricted to this
idealistic view of the universe. When we come across it for the first
time when we are young it appeals to us with all the force of exact
reasoning, and yet it has all the charm of paradox. There is no part
of our intuitive knowledge which appears to us to be more certain than
this distinction between ourselves and an outer environment: we know
that our conscious Ego is something different from our body--and we
know that outside our body there is something else. Yet the idealistic
view so appeals to the intellect that we cannot think speculatively
about it without, at times, almost convincing ourselves of the
unreality and shadowiness of all that at other times seems most real
and tangible; and we indulge in these speculations all the more readily
because we know that whenever we begin to _act_, the intuitively
felt body and outer world will return to us with all their original
conviction of reality.
Some such system of idealism must generally characterise a system of
philosophy founded on pure reasoning. We cannot but feel that the
universe that we construct is one that depends on our perceptions: it
is our perceptions. The essence of a thing is that it is perceived. If
there were no mind to perceive it, would it exist? The universe is our
thought, and we, that is our thought, exist only in the Thought of an
absolute Mind which we call God. Such is the metaphysics to which the
study of sensation led Berkeley.
The metaphysics of science has taken another turn. It is true
that men and women see something outside themselves which differs
slightly in different individuals--these differences are due to what
we call the “personal equation.” The image of the universe seen by
some individuals may differ profoundly from the image seen by some
others, or most others; but a well-marked gap separates these slight
individual deviations in the images seen by normal individuals from
the large deviations seen by those whose perceptions are what we call
pathological ones. The normal universe common to the majority of
men and women is an aggregate of molecules in motion. But this is a
conclusion with which modern physics has been unable to remain content,
for molecules must be able to act on each other across empty space, and
this is inconceivable. The universe therefore consists of a homogeneous
immaterial medium, the ether of space, and this is the true _substantia
physica_. Molecules and radiation are conditions of the ether, and for
the physicist it is the only reality. The “materialism” of our own
time is therefore the belief in the existence, unconditioned by time
or anything else, of the ether, or physical continuum; a homogeneous
medium, of which matter and energy, and the consciousness of the
organism, are only states or conditions.
The materialism of the twentieth century, like the idealism of
Berkeley, thus finds that there is something outside our own
consciousness that possesses absolute existence. To the materialist it
is the ether of space, and to Berkeley it is the existence of absolute
Mind. But if our desire to avoid metaphysics is a genuine one, we
must reject the notion of the universal ether no less than we must
reject the notion of an absolute Mind, and we must rest content with
pure phenomenalism. For each of us there can be no existence except
that which is perceived or conceptualised. There is nothing but our
own consciousness; there cannot even be an Ego which perceives; there
is only perception. We never do really believe this in spite of our
professions of reason. We find on strict self-analysis that we believe
that there is an Ego that perceives and that there are other Egos
that perceive, and that the universe which our Ego perceives is also
the same universe that other Egos perceive. If we did not believe that
there were other men and women that perceived--other consciousnesses
like our own, all that part of our own behaviour that we call morality
would be meaningless. In a philosophy of pure idealism other men and
women are only phenomena; only bodies moving in nature. Why, then,
should these elements of our consciousness influence the rest of our
consciousness as if they were men and women like ourselves. All this
amounts to saying that while our speculative thought suggests to us
that all that exists is our stream of consciousness, our actions must
convince us that there are other thinking individuals like ourselves.[5]
[5] The reader may recognise in this argument that of Driesch’s _Three
Windows into the Absolute_.
Even if we do surrender ourselves to phenomenalism and try to believe
that all that exists is our own consciousness, the fact of our duration
would suggest to us that this present consciousness is not all. Our
reality is not only that which is present in our minds now, but all
that was ever present in our mind. All that we have ever thought and
done persists and forms our conscious and unconscious experience. This
past of ours is something that is ever being added to, or becoming
incorporated with, our present state of consciousness; and if it is
something other than that which we now perceive and conceptualise, it
is something that has an existence of its own.
We must believe that there is something that we perceive, and not
that we merely perceive. For the phases of our immediate givenness,
that is, those things which were present in our minds from moment to
moment of the past were connected together and had direction, and this
direction was something that could not be influenced by our will, and
may even have been contrary to our will. Something that is very hot
always cools, a wheel that is revolving of itself always comes to a
stop, a pendulum ceases to swing, a stone that is rolling down a hill
continues to roll. Let us look back at a fire that was going out: it
is now nearly dead; let us start a pendulum to swing and then go away:
when we come back the pendulum is still swinging but the amplitude
of its vibrations is now less than it was; let us look away from the
stone that was falling: when we look again it is still falling but it
is not where it was. In all our givenness, in all the phenomena that
we perceive, there is something that is determined and unequivocal,
something that goes its own way apart from our consciousness of it.
Above all, we have the conviction of absoluteness in our sense of
personal identity. We, that is our Ego, are something that endures, and
we can trace no beginning to our identity, and we have no intuition
that it will cease to exist. Our Ego is now the same Ego that it was
in the past, and round it something has accumulated--the memories of
our former perceptions, and the habits that these have engendered. Did
our Ego create this from itself? Was it not rather a centre of action
which, residing in an existence other than itself--the absolute which
we call the universe--modified that existence and continually acquired
new relationships to it?
CHAPTER II
THE ORGANISM AS A MECHANISM
We propose now to consider the organism purely as a physico-chemical
mechanism, but before doing so it may be useful to summarise the
results of the discussions of the last chapter. Let us, for the moment,
cease to regard the organism as a structure--a “constellation of
parts”--and think of it as the physiologist does: it is a machine; it
is essentially “something happening.” What, then, is the object of its
activity? Whatever else the study of natural history shows us, it shows
us this, that the immediate object of the activity of the organism is
to adapt itself to its surroundings. It must master its environment,
and subdue, or at least avoid whatever in the latter is inimical. It
must avoid accident, disease, and death, it must find food and shelter;
it must seek for those conditions of the environment which are most
favourable to its prolonged existence. Ultimate aims--the preservation
of its race, ethical ideals--do not concern us in the meantime. The
main object of the functioning of the individual organism is that it
may dominate its environment, and obtain mastery over inert matter.
Consciously or unconsciously it acts towards this end.
All those actions which we call reflex, or automatic, or instinctive,
have this in common, that the organism in performing them comes into
relation with only a very limited region of its environment. But
knowing that region intuitively, its actions have a completeness
that an intelligent action does not exhibit until it has become so
habitual as to approach to automatic acting. The relations between
the organism and that part of its world on which it acts, intuitively
or instinctively, is something like that between a key and the lock
to which it is fitted: it opens this lock, perhaps one or two others
which resemble it, but no more. Now just because of this perfect, but
restricted, adjustment of the instinctive or automatically acting
organism to the objects on which it operates, knowledge of all else in
the environment becomes of little consequence.
It is clear that intelligent acting involves deliberation. The almost
inevitable motor response to a stimulus, which is characteristic of
the reflex or instinct, does not occur in the intelligent action:
instead of this we find that we choose between two or more responses
to the same stimulus. We reply to the latter by doing _this_ now,
and _that_ another time; and we see at once what results flow from
acting differently upon the same part of our environment, or acting in
the same way upon different parts. Perception, that is, knowledge of
the world, arises from acting; and as our actions, when carried out
intelligently, become almost infinitely varied, the environment appears
to us in very many aspects. In every action we modify that part of our
surroundings on which we operate. We can produce many modifications
that are of no use to us: these we do not attend to. We produce others
that are useful, and then we note the sequences of events involved in
our actions. Thus we discover or invent natural law--an environment
which is an orderly one. We can calculate and predict what will happen:
we produce, for instance, a _Nautical Almanac_, at once the type
of useful knowledge and of knowledge of sequences of events rigidly
determined--knowledge in short that is mechanistic; and which has been
engendered by the necessity for acting on our environment in our own
interests.
All this, the reader may note, is Bergson’s theory of intellectual
knowledge, a theory which, new and paradoxical at first, becomes more
and more convincing the longer we think about it, until at last it
seems so obvious that we wonder that it ever seemed new. Our modes of
thinking become constrained into certain grooves, just because these
modes of thinking have been those that were generated by our modes
of acting. So long as our thinking relates only to our acting, its
exercise is legitimate. But if its object is pure speculation its
results may be illusory, for a method has been applied to objects other
than those for which it was evolved. Let us now extend our intellectual
methods to the investigation of the organism. Necessarily we must
reason about the latter as a mechanism if we reason about it at all.
If it is a mechanism it must conform to the laws of energetics,
for science, so far as it is quantitative, whether its results are
expressed in the form of equations or inequalities, is based on these
principles.
The first principle of energetics,[6] or the first law of
thermodynamics, is that of the conservation of energy. Let us think
of an isolated system of parts such as the sun with its assemblage
of planets, satellites, and other bodies: in reality these do not
form an isolated system, but we can regard them as such by supposing
that just as much energy is received by them from the rest of the
universe as is radiated off by them to the rest of the universe. In
this system, then, the sum of a certain entity remains constant, and
no conceivable process can diminish or increase its quantity. We call
this entity energy, and we usually extend the principle of its absolute
conservation to matter, though this extension is unnecessary, for we
must think of matter in terms of energy. Stated more generally the
principle is that whatever exists must continue to exist, if we are to
regard this existence as a real one.[7]
[6] See appendix, p. 356.
[7] The principal reason why we do not believe in phantasms is that
these appearances _are not conserved_.
It is not at all self-evident to the mind that energy must be
conserved, for we see that, to all appearance, it may disappear. A
golf-ball driven up the side of a hill possesses energy while in
flight, kinetic energy or the energy of motion; but this apparently
is lost when the ball alights on the hill-top and comes to rest. We
say, however, that it now possesses potential energy in virtue of its
position; for if the hill is a steep one a little push will start the
ball rolling down with increasing velocity, and when it reaches the
spot from which it was originally impelled it possesses kinetic energy.
This is described as one-half of the mass of the ball multiplied by
the square of its velocity. Now the kinetic energy of the ball at
the instant when it left the head of the driver ought to be equal to
its kinetic energy when it reached the same horizontal level on its
downward roll. Yet it can easily be shown that this is not the case,
and we account for the lost kinetic energy by saying that it has been
dissipated by the friction of the ball against the atmosphere in its
flight, and against the side of the hill on its roll back. We cannot
verify this quantitatively, but we are quite certain that it is the
case. If we take a clock-spring and wind it up, the energy expended
becomes potential in the spring, and when the latter is released most
of it is recovered. But we may dissolve the spring in weak acid without
allowing it to uncoil. What then becomes of the energy imparted to it?
We are compelled to say that it has changed the physical condition of
the solution into which it passes, either becoming potential in this
solution, or becoming dissipated in some way. Yet again we cannot trace
this transformation experimentally though we may be quite sure that all
the energy potential in the coiled spring is conceivably traceable.
Suppose, again, we burn some hundredweights of coal in a steam-boiler
furnace. Heat is evolved which raises steam in the boiler, and the
steam actuates an engine, and the latter exhibits measurable kinetic
energy. Where did this come from? It was potential in the coal, we
say, though no method known to physics enables us to prove this by
mere inspection of the coal. We must cause the latter to undergo some
transformation. But by rigid methods we can estimate very exactly the
potential energy of the coal, and we can calculate the kinetic energy
equivalent to this. Yet again we find that the kinetic energy of the
steam-engine is only a fraction of that which calculation shows us
is the equivalent of the kinetic energy of the coal. What becomes
of the balance? We can be quite certain that it has been dissipated
in friction, radiation, loss of heat by conduction, loss of heat in
the condenser, and so on, although we cannot prove this rigidly by
experimental methods.
Think of the universe as an isolated system. It contains an invariable
quantity of energy. This energy may be that of bodies in motion--suns,
planets, cosmic dust, molecules, etc.--when it is kinetic energy;
or it may be the energy of electric charges at rest or in motion;
or any one of the many kinds of potential energy. It may pass
through numerous transformations--the chemical potential energy of
coal may be transformed into the kinetic energy of water molecules
(steam at high temperature), and this into the kinetic energy of the
revolving armature of a dynamo, and this again into the energy of
moving electrons (the current of electricity in the circuit of the
dynamo), and then again into the energy of ethereal vibration (light,
heat, X-rays, or other electro-magnetic waves), and these again into
mechanical or kinetic energy, and so on. When we say that we can
control energy we say that we can produce these transformations; we can
cause things to happen, we bring becoming into being. In this sense
energy is causality. But while the sum-total of energy in the universe
remains constant, the sum of causality continually diminishes. Energy
is the power, or condition, of producing _diversity_, but while energy
can suffer no diminution of quantity, diversity tends continually to
decrease.
In the last two sentences we state, in one way, the second law of
thermodynamics--in some respects the most fundamental result of our
experience in the physical investigation of the universe. In its most
technical form, as enunciated by Clausius, this law states that the
value of a certain mathematical function, called _entropy_,[8] tends
continually towards a maximum, when it is applied to the universe as a
whole. When we say the “universe,” we mean all that comes within our
power of physical investigation. Let us now see what this statement
means.
[8] See appendix, p. 369. Entropy is a shadowy kind of concept,
difficult to grasp. But again we may point out that the reader who
would extend the notion of mechanism into life simply _must_ grasp it.
The energy of the solar system is in part the kinetic energy of
those parts of it which are in motion--planets, planetesimals,[9]
and satellites. This quantity of energy is enormously great. In the
case of our earth it is 1/2(_mv_^2), _m_ being the mass of the earth,
and _v_ its velocity. Translated into numerical symbols we find this
quantity almost inconceivable. The greater part of this energy is
_unavailable_, that is, it can undergo no transformations. But because
the earth is in rotation at the same time as it revolves round the sun,
and because the moon revolves round the earth, there are tides in the
watery and atmospheric envelopes of the earth. The energy of the tides
is the kinetic energy of water or air in motion, and we can employ
this energy in the production of transformations, and it is therefore
_available_. But well-known investigations have shown that the tides
produce friction, and that the period of rotation of the earth is
slowly becoming greater. Ultimately the earth will rotate on its own
axis in the same time that it revolves round the sun--then a year and
day will be of the same length. When that occurs, the sun, earth, and
moon will be in equilibrium, and tidal phenomena due to the sun will
cease. The kinetic energy of the earth, rotating once in 24 hours is
obviously greater than its kinetic energy when rotating in the period
which will then be its year. What has become of the balance? It has
been transformed into the mechanical friction of the tides against the
surface of the earth,[10] and this friction has been transformed into
low-temperature heat, and this heat has been radiated off into space.
[9] Meteorites, cosmic dust, and other small particles moving in the
solar system within influence of the sun’s gravity.
[10] Not entirely, of course, but whatever be the transformation it
ends in heat production.
The solar system also contains energy in the form of the heated sun and
planets, and in the form of chemical potential energy of the substances
of which those bodies are composed. Let us think of the system, sun
and earth. The sun contains enormous heat energy, its temperature
being some 6000° C. absolute.[11] It contains enormous chemical energy
in the shape of compounds existing beneath its outer envelopes, and
it contains energy in the form of its own gravity--its contraction
together produces heat. But this heat is being continually radiated
away: chemical reactions must occur in which the potential chemical
energy of its substances must become transformed into heat, and this
heat is also radiated away; contraction of its mass must occur up to a
point when the materials are as closely packed together as possible;
heat is developed during the contraction, and this also passes away
by radiation. Suppose that modern speculations are well founded and
that radio-active substances are present in the sun: in the atomic
disintegration of these substances heat is produced and again radiated.
Therefore in whatever form energy exists in the sun, it transforms into
heat and this radiates. The ultimate fate of the sun is to cool down
and solidify. It will then move through space as a body having a cool,
solid crust, and an intensely heated interior. Slowly, very slowly,
this heated interior will cool down by the conduction of its heat from
the core to the outer shell, and by the radiation of this heat from the
shell into space. For incredibly long periods radio-active substances
in the interior must generate heat, but even this process must reach an
end.
[11] Absolute temperature is Centigrade temperature +273. This is, of
course not a full definition, but it is sufficient for our present
discussion.
The energy received by the earth is that of solar and stellar
radiation. Stellar radiation is minute, the absolute temperature
of cosmic space (or ether) being about -263° C. The absolute
temperature of the earth is about +17° C., so that it radiates off
more heat into space (other than that represented by the sun) than
it receives. All energy-transformations on the earth (except tidal
effects, and energy-conduction from the heated core, and possibly
radio-active effects) are transformations of this solar energy
received by radiation. We see these in oceanic and atmospheric
circulations (currents, winds, rainfall, etc.). We see them also in
the transformations of the chemical potential energy of coal and other
products of life--products in which the contained potential energy has
been absorbed from solar radiation.
Let us follow the transformations of this energy. Oceanic currents
transport heat from the equatorial sea-areas to the colder temperate
and polar areas, and compensatory polar currents flow towards the
equator, absorbing heat from the waters of temperate and equatorial
areas. Winds act in an analogous way. Water is evaporated where the
solar radiation is intense, and heat is absorbed in the transformation
of water into aqueous vapour. Then this water vapour is transported in
the winds into regions where it becomes condensed and precipitated as
rain or snow, heat being emitted in this condensation. In all these
movements there is friction, and this friction transforms to heat. In
all the effect is the general distribution over the earth of the heat
which the equatorial regions receive in excess of that which the polar
regions receive. Other mechanical effects are also produced by oceanic
and atmospheric circulations--the denudation of the coasts by tides and
storms, the erosion of the land by rivers, rains, snow, and ice, the
transport of dust in winds, etc. In all these friction is produced,
and this friction passes into heat.
The potential chemical energy which results from absorption of solar
radiation by plants is principally accumulated as coal. Apart from
the interference of man, this coal would slowly accumulate, perhaps
it would more slowly disappear by bacterial action, or by physical
transformations. In these transformations the energy of the coal
would become heat energy and the potential energy of the gas produced
by bacterial activity. By man’s agency the coal suffers other
transformations, and in the present phase of civilisation it is his
chief source of energy. It is available for doing work of many kinds,
and in all these forms of work it becomes transformed by chemical
action (burning) into high temperature heat.
We can cause this potential energy of coal to transform into mechanical
energy of machines, vehicles, and ships in motion by causing it to pass
into heat. In the steam-engine, or gas-engine, a highly heated gas
(steam, or the mixture resulting from the explosion of coal gas and air
in the cylinder of the engine) expands and propels a piston or rotates
a turbine. (Obviously in the petrol engine the same essential process
takes place.) We employ this kinetic energy directly in transport, or
we cause it to undergo other transformations. In the dynamo, kinetic
energy of machinery in motion transforms to electrical energy; and this
may transform to radiant energy (light, heat in electric radiators,
wireless telegraphy radiations), or it may transform to chemical
energy (the manufacture of carborundum in the electric furnace, for
instance), or it may transform again to the kinetic energy of bodies
in motion (electric traction). In innumerable ways the human power of
direction causes transformation of this accumulated potential energy,
and the reader will notice the analogy of all this with the essential,
unconsciously expressed activity of the animal organism in its own
metabolism--a point to which we return later.
Notice now that all the energy-transformations we have noticed are
_irreversible_. This is a matter of deep philosophical importance,
and we must devote some time to it. Consider first of all the working
of the steam-engine; what occurs is this--coal is burned in the
boiler-furnace, that is to say, potential chemical energy passes
into heat and this vaporises water in the boiler, producing a gas
at high temperature (steam). This gas expands in the high-pressure
cylinder of the engine, driving forward a piston; it expands further
in the intermediate cylinder, propelling its piston also, and again
in the low-pressure cylinder. It is then cooled by passing through
the condenser, and in the contraction further mechanical energy
is obtained. The train of events thus begins with a gas at a high
temperature and ends with the same gas at the temperature of the water
in the condenser. The heat lost is transformed into the mechanical
energy of the engine. But not all of it. A certain quantity is lost
by radiation from the boiler walls, the walls of the steam-pipes, the
cylinders, and other parts of the engine; also some of the energy is
transformed to friction, and this again to heat. In this way a very
considerable part of the energy contained in the coal is frittered away
in unavoidable heat-conduction and radiation, and a last residue of it
goes down the drain, so to speak, with the condenser water. This loss
is inherent in the nature of the mechanism of the engine.
Suppose that the energy of the engine is employed to drive a dynamo.
The armature of the latter rotates against the constraint of powerful
electro-magnets, and in so doing a current of electricity is generated.
By the law of conservation this current should contain as much energy
as was put into the rotation of the armature; as a matter of fact it
does not, and the deficiency is represented by the friction of the
parts of the machine against each other, by imperfect conductivity of
electricity in the wires, and by imperfect insulation of the current.
Friction, imperfect conductivity, and imperfect insulation all
transform to heat, and this radiates away. Suppose now that the current
is used for lighting purposes: to do this it must heat the metallic
filaments in the lamps, or the points of the carbons in an arc. This
heat then transforms to light, but along with the light, which was the
object of the transformation, heat is produced, and this heat radiates
away.
The actual process in which the particular form of energy required is
generated may or may not be reversible in theory. That employed in
the steam-engine is not, for if we start with a cold boiler and then
work the engine backwards we could not raise steam. The process in the
dynamo is theoretically reversible: if we send a current of electricity
into a dynamo the machine will begin to rotate, and become a motor, so
that we can obtain mechanical work from it. Now in theory all forms of
energy are mutually convertible, and all can be expressed in terms of
a common unit. The unit of mechanical energy is called the _erg_: let
a current, the energy of which is equal to _N_ ergs, be sent into the
dynamo, then we ought to obtain from the latter mechanical energy equal
to _N_ ergs. Conversely, if _N_ ergs of mechanical energy be employed
to rotate the dynamo, we should obtain electrical energy equal to this
amount. Now as a matter of fact we do not obtain these theoretical
conversions, for some of the electrical energy is dissipated when we
employ the machine as a motor, and some of the mechanical energy is
likewise dissipated when we employ it as a dynamo.
The entity that we call energy is the product of two factors, a
capacity-factor and an intensity-factor. Thus:--
Mechanical energy = quantity of water × height at which it is
of water power situated above the water-motor.
Energy of an = quantity of electricity × electrical potential.
electric current
Chemical energy = equivalent weight of the substance ×
chemical potential.
What is it that determines whether or not an energy-transformation will
occur? It is the condition that a difference of the intensity-factors
of the energy in different parts of a system exists. Water will
flow from a higher to a lower level, doing work as it flows, if
it is directed through a motor. Electricity will flow if there is
a difference of electrical potential. A chemical reaction will
occur if two substances before interacting possess greater chemical
potential than do the products which may possibly be formed during the
interaction. Coal and oxygen possess greater chemical potential than do
carbon dioxide and water, therefore they will combine, forming carbon
dioxide and water. Energy-transformations will therefore occur wherever
it is possible that differences of intensity or potential can become
abolished. The energy that may thus flow from a condition of high to a
condition of low potential, undergoing a transformation as it flows, is
the available energy of the system of bodies in which it is contained.
A closed vessel surrounded by an envelope impervious to heat, and
containing a mixture of oxygen and hydrogen, is an isolated system
containing available energy. Let the mixture be fired by an electric
spark, and heat is evolved. The total energy of the system is unaltered
in amount, but the available energy has disappeared, since the heated
water vapour is incapable of undergoing further transformations while
it forms part of its isolated system.[12]
[12] It is really necessary to lay stress on the distinction between
available and unavailable energy, as it is one which many biologists
appear to ignore. Thus, a popular book on the making of the earth
attempts to argue that essential distinctions between living and
inorganic matter are non-existent. One of these distinctions is that
organisms absorb energy, and this author points to the absorption
of “latent heat” by melting ice as an example of the absorption of
energy in a purely physical process. Consider a system consisting
of a block of ice and a small steam boiler. We can obtain work
from this by the melting of the ice--that is, its “absorption of
latent heat.” The system, ice at 0° C. + steam at 100° C., possesses
available energy, but the system, melted ice + condensed steam, both
at the same temperature, contains none. The molecules of water at
0° C. “absorb energy,” that is to say, their kinetic energy becomes
greater, but their available energy in the system has disappeared. In
saying that the organism absorbs energy, we mean, of course, that it
accumulates available energy, that is, the power of producing physical
transformations. (See further, appendix, p. 366.)
All physical processes are therefore _irreversible_, that is to say,
proceed in one direction only. Either a process is irreversible in
the sense that it cannot proceed both in the positive and negative
directions (a steam-engine, for instance), or it is irreversible in
the sense that while it proceeds the energy involved in it becomes
less capable of being transformed into other conditions. (In the
theoretically reversible dynamo, energy becomes dissipated in the form
of heat.) The following statements may be regarded as axioms[13]:--
[13] Bryan, _Thermodynamics_: Teubner, Leipzig, 1907, p. 40.
(1) “If a system can undergo an irreversible change, it will do so.”
(2) “A perfectly reversible change cannot take place by itself.”
In the phenomena studied by physics we see only irreversible
changes. In all these processes energy descends the incline, and some
(considerable) fraction of the amount involved passes into conditions
in which it is incapable of further transformation; in all, energy
becomes less and less available. Expressed in its most technical form,
the second law of thermodynamics states that entropy tends continually
to increase. Every such process as we can study in physics “leaves an
indelible imprint somewhere or other on the progress of events in the
universe considered as a whole.”[14]
[14] Bryan, _Thermodynamics_, p. 195.
We cannot observe a truly isolated system. The earth itself is part of
the solar system, and the latter receives energy from, and radiates
it to the rest of, the universe. Our only isolated system is the
whole universe. We must think of it, in so far as we regard it as
physical, as a finite system: if it is infinite, our speculations
become meaningless. The universe therefore is a system in which energy
tends continually towards degradation. In every process that occurs
in it--that is to say every purely physical process--heat is evolved,
and this heat is distributed by conduction and radiation, and tends
to become universally diffused throughout all its parts. When this
ultimate, uniform distribution of energy will have been attained,
all physical phenomena will have ceased. It is useless to argue that
universal phenomena are cyclical. We vainly invoke the speculations
(founded on rather prematurely developed cosmical physics) of stellar
collisions, light-radiation pressure, the distribution of cosmic
dust, etc. to support our notions of alternate phases of dissipation
and concentration of energy; close analysis will show that all these
processes must be irreversible. The picture physics exhibits to us
is that of the universe as a clock running down; of an ultimate
extinction of all becoming; an universal physical death.
In this conclusion there is nothing that is speculative. It is the
least metaphysical of the great generalisations of science. It
represents simply our experience of the direction in which physical
changes are proceeding. Based upon the most exact methods of science
known to us, nothing seems more certain and more capable of rigorous
mathematical investigation.
And yet we are certain that it is not universally true. For there
must always _have been_ an universe--at least our intellect is
incapable of conceiving beginning. If we suppose a beginning, an
unconditioned creation, at once we leap from science into the rankest
of metaphysics. Holding, then, that the duration of our physical
universe is an infinite one, we see that the ultimate attainment of
energy--dissipation--must have occurred if our physics is true. It does
not matter what new sources of energy modern investigation has shown
to us; nor do the incredibly great lapses of duration necessary for
the depletion of these sources matter. We have eternity to draw upon.
Everywhere in the universe we see diversity and becoming. Is then the
whole problem a transcendental one, or is the second law untrue? We
refuse to regard the problem as insoluble, and we must think of the
second law as true of our physical experience only. But our conception
of the universe shows that it cannot be true, and so we have to seek
for an influence compensatory to it.
If the organism is a mechanism of the physico-chemical kind, it should
therefore conform to the two great principles of energetics established
by the physicists. Now there can be no doubt that the law of
energy-conservation does apply to all the processes observed in animals
and plants. Let us consider the “calorimetric experiments.” An animal,
together with the food and oxygen supplied to it, and the various
substances excreted by it, constitutes a physical system. This system
can be approximately isolated so that no heat enters it from outside,
while the heat that leaves it can be determined quantitatively. The
animal is made to perform mechanical work, and this is measured. The
energy-value of the food ingested by it, and that of the excreta, can
be estimated. All the physical conditions can thus be controlled,
and the results of such experiments show that energy is conserved.
The energy contained in the food is greatly in excess of the energy
contained in the excreta, but the deficit is quantitatively represented
by the work done by the animal, and by the heat lost in conduction
and radiation from its body. The difference between the observed
results and the theoretical ones are within the limits of error of the
experiment. The metabolism of the animal as a whole, then, conforms to
the law of conservation, and the general results of physiology all go
to show that this is also true of chemico-physical changes considered
in detail.
It cannot be shown that the second law, that of the dissipation of
energy, applies to the organism with all the strictness in which
it applies to purely physical systems. If we consider only the
warm-blooded animal we do indeed find that its general metabolism
does proceed in one direction, and that irreversible changes occur.
In the mammal and bird we have organisms which present a superficial
resemblance to the heat-engine, with respect to their chemico-physical
processes, a resemblance, however, which is rather an analogy than an
identity of processes. In the heat-engine we have (1) a mechanism of
parts which do not change in material and relationships to each other
(boiler, cylinder, pistons, cranks, slide-valves, etc.); and (2) a
working substance (the steam).
Energy in the form of the chemical potential of coal and oxygen is
supplied to the mechanism. The coal is oxidised, producing heat. The
heat then expands the working substance (the water in the boiler),
and this working substance--now a gas at high temperature and
pressure--propels the piston and confers kinetic energy on the engine.
Note the essential steps in this process: substances of high chemical
potential (coal and oxygen) suffer transformation into substances of
low chemical potential (carbon dioxide and water), and the difference
of energy appears as high-temperature heat (increased kinetic energy
of water molecules, to be more precise). This heat is then transformed
into mechanical work (the kinetic energy of the molecules of steam
is imparted to the piston of the engine). But in this transformation
only a relatively small proportion (10% to 20%) of the energy
available is transformed into mechanical work: the rest is dissipated
as irrecoverable low-temperature heat, by radiation from boiler,
steam-pipes, engine, and as the heat which passes into the condenser
water.
In the organism in general there is no distinction between the fixed
parts of the mechanism and the working substance. The organism
itself (its muscles, nerves, glands, etc.) _is_ the working
substance. Further, it is not quite certain that there is a necessary
transformation of chemical energy into heat. The source of energy in
the case of the warm-blooded animal is the chemical energy of the food
substances and oxygen taken into its body. These chemical substances
undergo transformations in the alimentary canal and in the metabolic
tissues. The proteids of the food are broken down into amino-substances
in the alimentary canal, and these amino-substances are synthesised
into the specific proteids of the animal’s body. Corresponding changes
occur with the carbohydrates and fats ingested. These rearrangements
of the molecular structure of the foodstuffs are the object of the
processes of digestion and assimilation; and when they are concluded,
a certain proportion of the food taken into the body has become
incorporated with, or has actually become a part of, the living tissues
(muscles, nerves, etc.) of the animal body. This living substance,
compounds of high chemical potential (proteids, carbohydrates, and
fats) undergoes transformation into compounds of low chemical potential
(water, carbon dioxide, and urea). There is a difference of energy, and
this appears as mechanical energy, as the chemical energy required for
glandular activity, and as heat.
We must not, however, conclude that this heat of the warm-blooded
animal is comparable with the waste heat of the steam-engine. The
homoiothermic animal maintains its body at a constant temperature,
which is usually higher than that of the medium in which it lives,
and this constancy of temperature obviously confers many advantages.
Chemical reactions proceed with a velocity which varies with the
temperature, so that in the warm-blooded animal the processes of life
go on almost unaffected by changes in the medium. The animal exhibits
complete activity throughout all the seasons of the year. It does not,
or need not, hibernate, and it can live in climates which are widely
different. We therefore find that the most widely-distributed groups
of land-animals are the warm-blooded mammals and birds, while the
largest and most cosmopolitan marine animals are the warm-blooded
whales. Heat-production in the mammals and birds is therefore a
direct object of the metabolism of the animal; it is a means whereby
the latter acquires a more complete mastery over its environment.
That it is not necessarily a step in the transformation of chemical
into mechanical energy we see by considering the metabolism of the
cold-blooded animals. In these poikilothermic organisms the body
preserves the temperature of the medium. The temperature in such
animals may be a degree, or a fraction of a degree, higher than that of
the environment, but, in the absence of exact calorimetric experiments,
we cannot say what proportion of the energy of the food of these
animals passes into unavailable food energy. Probably it is a very
small fraction of the whole, and we are thus justified in saying that
in the cold-blooded animal chemical energy does not, to a significant
extent, become transformed into heat. The result is, of course, that
the vital processes in these organisms keep pace, so to speak, with the
temperature of the environment, since the chemical reactions of their
metabolism are affected by the external temperature. We find therefore
that hibernation, the formation of resting stages, and a general
slowing down of metabolic processes are more characteristic of the
cold-blooded animal during the colder seasons than of the warm-blooded
animal. The former has not that mastery over the environment attained
by the mammal or bird.
The metabolism of the animal therefore resembles the energy process
of the heat-engine only in the general way, that in both series of
transformations chemical energy descends from a condition of high
potential to a condition of low potential, transforming into mechanical
energy in so doing, and thus performing work. In the heat-engine
chemical energy transforms to heat, and then to mechanical energy, and
of the total quantity transformed a certain large proportion suffers
dissipation by conversion into low-temperature heat. In the animal
organism chemical energy transforms directly to mechanical energy
without passing through the phase of heat. If heat is produced it is
because it is, in a way, available energy, inasmuch as it permits of
the continuance of chemical reactions at a normal rate. The analogy of
the animal with the heat-engine is therefore a false one. It suggests
oxidation of the food-stuffs and heat production, whereas it is not
at all certain that any significant proportion of the energy of the
organism is the result of oxidation: many animal organisms indeed
function in the entire absence of free oxygen. Further, the proportion
of energy dissipated is always small compared with the heat-engine,
and tends to vanish. The second law of thermodynamics does not,
then, restrict the energy-transformations of the animal organism to
the same extent that it restricts the energy-transformations of the
physico-chemical mechanism.
The processes involved in the plant organism differ still more in
their _direction_ from those of a “purely physical” train. To see this
clearly we must consider the imaginary mechanism known as a Carnot
heat-engine.[15] This is a system in which we have (1) a heat-reservoir
at a constant high temperature, (2) a refrigerator at a constant low
temperature, and (3) a working substance which is a gas. Energy is
drawn from the reservoir in the form of heat, and this heat expands the
gas, doing work. The gas contracts, and its heat is then given up to
the refrigerator. The work done is equal to the difference between the
amount of heat taken from the reservoir and the amount given to the
refrigerator.
[15] See appendix, p. 363.
This series of operations is called a direct Carnot cycle. But the
mechanism can be worked backwards. In this case heat passes from
the refrigerator into the working substance, which was at a lower
temperature. The working substance, or gas, is then compressed, as the
result of which operation it is heated to just above the temperature
of the reservoir. The heat it thus acquires is then given up to the
reservoir.
In the direct Carnot cycle, therefore, energy passes from a state of
high potential to a state of low potential and work is done _by_ the
mechanism. In the reversed Carnot cycle energy passes from a state of
low potential to a state of high potential and work is done _on_ the
mechanism. The Carnot engine is thus perfectly reversible. No energy
is dissipated in its working. It is, of course, a purely imaginary
mechanism.
In the metabolism of the green plant carbon dioxide and water are
taken into the tissues of the leaf and are transformed into starch.
But the energy of the compounds, carbon dioxide and water, is much
less than that of the same compounds when built up into starch. Energy
must therefore be derived from some source, and this source is said
to be the ether. Solar radiation is absorbed by the green leaf, and
this energy is employed to produce the chemical transformation. Just
how this is effected we do not positively know, in spite of much
investigation. It is possible that formaldehyde is formed from carbon
dioxide and water, polymerized, and then converted into starch. It is
possible that the absorbed electro-magnetic vibrations are converted
into electricity in the chlorophyll bodies of the leaf, though when
radiation is absorbed in physical experiments it is converted into
heat. We do not know just what are the steps in the transformation,
though it is clear that solar radiation is absorbed and that the
chlorophyll of the leaf is instrumental in converting this energy of
radiation into chemical potential energy. But the important thing to
notice is, that we have here a process closely analogous to that of a
reversed Carnot engine. Energy (that of the carbon dioxide and water)
passes from a state of low potential to a state of high potential (that
of the energy of starch), and work is done _on_ the plant in producing
this transformation.
Work is not done _by_ the green plant. This statement is not, of
course, quite rigidly true, for a certain amount of mechanical work
is done by the plant. Flowers open and close; tendrils may move and
clasp other objects; there is a circulation of protoplasm in the plant
cells, and a circulation of sap in the vessels of stems, etc. Also work
is done against gravity in raising the tissues of the plant above the
soil, while work is also done by the roots in penetrating the soil. But
when compared with the work done by radiation in producing the chemical
transformations referred to above, these other expenditures of energy
must be insignificant. Speaking generally, then, we may describe the
green plant as a system in which available energy is accumulated in
the form of chemical compounds of high potential. It is, further, a
system in which energy becomes transformed without doing mechanical
work, except to a trifling extent, and in which there is no formation
of heat, or at least in which the quantity of heat dissipated is only
perceptible during very restricted phases, is relatively small during
the other phases, and tends to vanish.
Let us now combine the processes of plant and animal; we start with
the latter. In it we have a mechanism which does work. The source of
its energy is the potential chemical energy of its foodstuffs, which
latter reduce down to those substances known as proteids, fats, and
carbohydrates. The energy-value of these compounds is considerable,
that is to say, if they are burned in a stream of oxygen a large
quantity of heat is obtained from their combustion. They are ingested
by the animal, broken down chemically, and rearranged. The proteids
eaten by the animal (say those of beef or mutton or wheat) are acted
upon by the enzymes of the alimentary canal and are decomposed into
their immediate constituents, amino-acids, and then other enzymes
rearrange these amino-acids so as to form proteid again, but proteids
of the same kinds as those characteristic of the tissues. This
decomposition and re-synthesis is carried out also with respect to the
fats and carbohydrates ingested. The result is that the food taken into
the alimentary canal, or at least a part of it, is built up into the
living substance of the animal’s body. The energy expended upon these
processes of digestion and assimilation is probably inconsiderable.
During these processes the animal absorbs available chemical energy.
The energy thus taken into the animal is then transformed. The major
part of it appears as mechanical energy--that of bodily movement, the
movements of heart, lungs, blood, etc.--and heat. Some part of it
becomes nervous energy, by which rather vague term we mean the energy
involved in the propagation of nervous impulses. Some of it is used
in glandular reactions, in the formation of the digestive juices, for
instance. The most of it, however, transforms to mechanical energy
and heat. Just how these energy transformations are effected we do
not know. The heat is, of course, the result of chemical changes,
oxidations, decompositions, or changes of the same kind as that of the
dilution of sulphuric acid by water, but the mechanical energy appears
to result directly from chemical change without the intermediation of
heat. We shall return to this point in a later chapter, and content
ourselves with saying here that the chemical compounds contained in
the metabolic tissues of the animal body undergo transformation from
a state of high to a state of low chemical potential, and that this
difference of potential is represented by the work done and the heat
generated. The proteid, fat, and carbohydrate of the tissues represent
the condition of high potential; and the carbon dioxide, the water, and
the urea, into which these substances are transformed, represent the
condition of low potential.
Let us suppose a Carnot heat-engine in which the temperature of the
reservoir of heat is (say) 120°C., and that of the refrigerator 50°C.
The heat of the refrigerator can still be made a further source of
energy by constituting it the heat reservoir of another Carnot engine
which has a refrigerator at a temperature of 0°C. Our animal organism
may be compared with a Carnot cycle; its energy reservoir is the
proteid, fat, and carbohydrate ingested, and its refrigerator (or
energy sink) is the carbon dioxide and urea excreted. Now the urea of
the higher mammal becomes infected with certain bacteria, which convert
it into ammonium carbonate. Another species of bacteria converts the
ammonia into nitrite, and yet another turns the nitrite into nitrate.
The main process of the animal is therefore combined with several
subsidiary ones.
_Carbohydrate_, _fat_, _proteid_ } Metabolism
break down into } of the animal
↓
Carbon dioxide
Water
Urea------_Urea_ } Metabolism of
Chemical ↓ } urea bacteria
Energy at passes into
high potential ammonium
\ carbonate----_ammonium_ } metabolism
\ _carbonate_ } of nitrifying
\ ↓ bacteria
\ oxidises to
Work done by \ nitrite----_Nitrite_ } Metm. of
the system \ ↓ } nitrifying
\ oxidises } bacteria
\ to nitrate}
chemical energy
at low potential
The arrows show that energy is descending the incline indicated by a
direct Carnot cycle. There is no more work to be obtained from the
carbon dioxide and water excreted by the mammal, but more work can be
obtained from the urea when it is used by bacteria, and “ferments”
to ammonia. Work can again be obtained from the ammonia by bacteria,
which convert it into nitrite, and yet again from the nitrite by other
bacteria, which convert it into nitrate. The nitrate represents the
energy-zero so far as the organisms considered are concerned.
Other nitrogenous residues are contained in the urine of animals,
and several other excretory products may be formed. But in all
these cases we can easily find subsidiary energy-transformations
effected by bacteria, as in the above scheme. This, then, is the
positive, or direct half, of that reversible Carnot cycle with
which we are comparing life. In it energy falls in potential (or
intensity, or level), and in this fall of potential transformations
are produced--exhibit themselves, is perhaps a better way of putting
it. We will consider these transformations later; in the meantime it
should be noted that in this fall of potential is a degradation of
chemical energy. Compounds, carbon dioxide, water, and nitrate are
produced which are chemically inert. It is no use to say that carbon
dioxide may react with (say) glowing magnesium, water with metallic
sodium, and nitrate with (say) glowing carbon. A condition of chemical
equilibrium would result from purely inorganic becoming on our earth in
which there was no metallic sodium or magnesium or incandescent carbon;
in which the metals would become inert oxides, and the carbon would
become dioxide. The formation of these compounds represents a limit to
energy-transformations. Note also that all these energy-transformations
are conservative; the total quantity remains unchanged throughout,
and is the same at the end as at the beginning. But _entropy has been
augmented: unavailable energy has increased at the expense of available
energy_.
Consider now the indirect, or reversed, Carnot cycle. We begin with
the inert matter, resulting from the metabolism of the animal, carbon
dioxide, water, nitrate, and a few more mineral substances. We have the
energy of solar radiation. By virtue of the living chlorophyll plastid
in the cells of the green plant, this solar radiation uses the carbon
dioxide and water as raw materials in the elaboration of starch. At the
same time it absorbs nitrate, with some other inert mineral substances
from the soil, and takes these into its tissues. The starch formed
in the chlorophyll is converted into soluble sugar, which circulates
through the vessels of the plant and is associated with the nitrogenous
salt in the elaboration of proteid. Proteid, oils, fats and resins,
and to a greater extent carbohydrates, are thus built up by the plant
and _accumulate_, for mechanical work is not done by it, nor is heat
dissipated--or at least these processes occur to an insignificant
extent.
} Metabolism --------------> are synthesised to--
Carbon dioxide } of the { proteid
Water } green { fat
Nitrate } plant { carbohydrate
Chemical energy at --------------> Chemical energy
low potential Work done on at high potential.
the system
The “working substance” of our organic cycle has therefore returned to
its original state.
We have considered the process of metabolism in two categories of
organisms, the typical animal and the green plant, and we have
combined these so as to obtain a picture of a reversible cycle of
physico-chemical processes. When we speak of the “organism” in the
most general sense, we mean that it exhibits these two modes of
metabolism. This is, of course, not the case in any actual organism
which we can investigate, or at least the typical modes of behaviour
which characterise animal and plant life are not seen in any one
individual. But we find that there is no absolute distinction between
the two kingdoms. The plant may exhibit a mode of nutrition closely
resembling that of the animal (as in the insectivorous plants), and it
is possible that photo-synthetic process, in the general sense, may
be present in the metabolism of some animals. Certain lower plants,
the zoospores of algæ, exhibit movements identical in character with
those of lower animals. At the base of both kingdoms are organisms,
the Peridinians, for instance, which have much of the structure of the
animal (though cellulose is present in their skeleton), which possess
motile organs, but which also possess a photo-synthetic apparatus,
and exhibit the typical plant mode of nutrition. Further, there are
symbiotic partnerships, that is, associations of plant and animal
in one “individual” form (as, for instance, among the lower worms,
Echinoderms, polyzoa, molluscs, and other groups of animals). In these
cases green algal cells, capable of forming starch from carbon dioxide
and water under the influence of light, become intercalated among
the tissues of the animal. We find, also, that with regard to some
fundamental characters, plant and animal display close similarities:
the structure of the cell, for example, and the highly special mode of
conjugation of the germ-nuclei in sexual reproduction. We must regard
all the distinctive characters of the plant as represented in the
animal and _vice versa_. Why they have become specialised in different
directions is a question that we discuss later.
The organism, then, in so far as we regard it as a physico-chemical
mechanism, as the theatre of energetic happenings, exhibits the
following general characters:--
(1) It slowly accumulates available energy in the form of chemical
compounds of high potential, work being done upon it.
(2) It liberates this energy in relatively rapid, controlled,
“explosive reactions,” transforming into movements carried out by a
sensori-motor system of parts, work being done by it.
(3) In all these transformations the amount of energy which is
dissipated is relatively small, and tends to vanish.
From the point of view, then, of energetic processes these are the
characters of life, using the term in the general sense indicated
above.[16]
[16] This is, of course, the argument of part of Chapter II. of
Bergson’s _Creative Evolution_. The reader will not find the essential
differences between plants and animals stated so clearly anywhere else
in biological literature.
Is there an absolute distinction between the organic mechanism and
the inorganic one? Let us note, for the first time, that the actual
physico-chemical transformations _themselves_, which we study in
inorganic matter, are identical with those which we study in the
organism. Molecules of carbon dioxide, water, nitrate, sodium chloride,
potassium chloride, phosphate, and so on, are just the same in inert
matter as in the organism. Chemical transformations, such as the
hydrolysis of starch, the inversion of cane sugar, or the splitting of
a neutral fat, are certainly just the same processes, whether we carry
them out in the glass vessels of the laboratory, or observe them to
proceed in the living tissues of the animal body. The same molecular
rearrangements, and the same transfers of energy, occur in both series
of events. This, however, is not the material of a distinction: what we
have to find is, whether the _direction_ of a group of physico-chemical
reactions is the same in the organism and in a series of inorganic
processes.
Let us return to the Carnot cycle. This is a series of operations which
occur in an imaginary mechanism in such a manner that the whole series
can be easily reversed. Heat is supplied to the imaginary engine,
which then performs work and yields up its heat to a refrigerator.
Work is then performed on the engine, which thereupon takes heat from
the refrigerator and returns it to the source. The work done _by_
the engine in the direct cycle is equal to the work done _on_ it in
the indirect cycle. The heat taken from the source and given to the
refrigerator in the direct cycle is equal to the heat taken from the
refrigerator and given to the source in the indirect cycle. But it
is a purely imaginary mechanism, and all experience shows not only
that it has not been realised in practice, but that it cannot so be
realised. If it could be realised, we should show that the second law
of thermo-dynamics is not physically true.
Do the energy processes of life realise such a perfectly reversible
cycle of operations? In order to answer this question we must consider
the fate of the energy which is absorbed in the plant metabolic cycle,
and that which is given out in the animal one. Does _all_ the energy of
solar radiation which is absorbed by the plant pass into the form of
the potential chemical energy of the carbohydrates and other substances
manufactured? Does any of the energy of the animal which results from
the metabolism of its body pass into the unavailable form--that is,
into a form in which it cannot be utilised by other organisms? That is
to say, is energy dissipated by the organism?
Undoubtedly it is to some extent, but to a far less extent than in the
inorganic train of processes. Some of the energy of solar radiation
absorbed by the plant must become transformed, by the friction of
whatever movements occur, into low-temperature heat, and some quantity
of heat, however small, is generated by the metabolism of the plant.
Again, some of the heat of the warm-blooded animal must be radiated
into space, or conducted away from its body; and this energy becomes
dissipated--let us assume, at least, that it is so dissipated in the
physical sense. Probably also some quantity of heat is generated by
the metabolism of the cold-blooded animal, though this must be a
very small proportion of the total energy transformed. We see, then,
that the distinction is one of degree, though the difference between
inorganic and organic energetic processes is very great in this
respect; so great that we must regard it as constituting a fundamental
difference, and as indicative of the limitation of the second law when
extended to the functioning of the organism.
But we have also to consider the effect of the work done by the
organism. We consider the nature and meaning of the evolutionary
process in a later chapter, but in the meantime we may state this
thesis: that the process of evolution leads up to man and his activity.
It _leads_, if we regard the process as a _directed_ one; but even if
we regard it as a fortuitous process we still find that man, far more
than any other organism, is the result of it. All the facts of biology
and history show that man dominates the organic world, plant or animal;
that the whole trend of his activity is to eliminate whatever organisms
are inimical, and to foster those that are useful. Already, during the
brief period of his rational activity, the wolf has disappeared from
civilised lands while the dog has been produced. Species after species
of hostile or harmful organisms have been, or are being, destroyed or
changed, while numerous other species have been preserved and altered
for his benefit. In the future we see an organic world subservient to
him either entirely or to an enormous extent.
So also in the inorganic world. Rivers which formerly rushed down
through rapids, dissipating their energy of movement in waste
irrecoverable heat, now pour through turbines and water wheels,
generating electricity and accumulating available energy. Winds
which “naturally” dissipated their mechanical energy in waste heat
now propel ships and windmills. Tides, with their incredibly great
mechanical energy, now simply warm up the crust of the earth by an
infinitesimal fraction of a degree daily, and produce heat which at
once radiates into space. Who doubts that by and by this energy too
will become accumulated for human use? Multitudes of chemical reactions
were potential, so to speak, in the molecules of petroleum, while the
energy which might have produced them ran to waste. But under human
activity this energy became directed and made to produce chemical
reactions formerly existing only in their possibility, and all the
substances of modern organic chemistry came into existence.
The energy, then, of human activity has been directed towards averting
or retarding the progress towards dissipation, or irrecoverable waste,
of cosmic energy--that of the sun’s radiation, and of the motions
of earth and moon. Human activity has accumulated available energy.
The difference of water-level between Niagara and the rapids below
represents available mechanical energy. A few years ago an enormous
quantity of this energy became irredeemably lost in waste heat every
twenty-four hours: now it remains available for work; and this quantity
of work retained is enormously greater than is the human energy which
was expended on erecting the water-power installation there.
The processes studied by physics and chemistry are therefore
irreversible ones. We can conceive a perfectly reversible process,
as in the Carnot heat-engine, but this is a purely intellectual
conception, formed as the limit to a series of operations which
approximate closer and closer to an ideal reversibility. It is a
conception that has no physical reality--a guide to reasoning only. On
the other hand we see that all naturally occurring physical processes
are irreversible and in their sum tend to complete degradation of
energy. Mechanistic biology isolates physico-chemical processes in the
functioning of the organism, and sees that they conform to the law of
dissipation, as well as to that of the conservation of energy.
Yet the organism as a whole, that is, life as a whole, on the earth,
does not conform to the law of dissipation. That which is true of the
isolated processes into which physiology decomposes life is not true of
life. In all inorganic happenings energy becomes unavailable for the
performance of work. Solar radiation falling on sea and land fritters
itself away in waste irrecoverable heat, but falling on the green plant
accumulates in the form of available chemical energy. The total result
of life on the earth in the past has been the accumulation of enormous
stores of energy in the shape of coal and other substances. By its
agency degradation has been retarded. Whenever, says Bergson, energy
descends the incline indicated by Carnot’s law, and where a cause of
inverse direction can retard the descent, there we have life.
CHAPTER III
THE ACTIVITIES OF THE ORGANISM
The rather lengthy discussion of the last chapter was necessary in
order to show just how far the principles of energetics established by
the physicists applied to the organism. We have seen that the first law
of thermodynamics does so apply with all its exclusiveness. The more
carefully a physiological experiment is made; the more closely do its
results correspond with those which theory demands. It is true that
relatively few experimental investigations can be controlled in this
way, but in those that can be checked by calculation (as, for instance,
in the well-known calorimetric experiments) everything tends to show
that precisely the same quantities of matter and energy enter the body
of an organism in the form of food-stuff, that leave it as radiated and
conducted heat, as work done, and as the potential chemical energy of
the excretions. Even when we are unable (as in most investigations) to
apply the test of correspondence with theory, we have the conviction
that the law of conservation holds with all its strictness.
Then, whenever it was possible to apply the methods of chemistry and
physics to the study of the organism, it was seen that the processes
at work were chemical and physical. The substance of the living body
was seen to consist of a large (though limited) number of chemical
compounds, differing mainly from those which exist in inorganic nature
in their greater complexity. It was also seen that physico-chemical
reactions occurred in living substance analogous with, or quite
similar to, those which could be studied in non-living substance. The
conclusion, then, was irresistible that the life of the organism was
merely a phase in the evolution of matter and energy, and differed in
no essential respect from the physico-chemical activities that could be
observed in the non-living world.
These conclusions were stated so well by Huxley in his famous lecture
on “The physical basis of life,” over forty years ago, that all
subsequent utterances have been merely reiterations of this thesis in
a less perfect form. The existence of the matter of life, Huxley said,
depended on the pre-existence of certain chemical compounds--carbonic
acid, water, and ammonia. Withdraw any one of them from the world
and vital phenomena come to an end. They are the antecedents of
vegetable protoplasm, just as the latter is the antecedent of animal
protoplasm. They are all lifeless substances, but when brought together
under certain conditions they give rise to the complex body called
protoplasm; and this protoplasm exhibits the phenomena of life. There
is no apparent break in the series of increasingly complex compounds
between water, carbon dioxide, and ammonia, on the one hand, and
protoplasm on the other. We decide to call different kinds of matter
carbon, oxygen, hydrogen, and nitrogen and to speak of their activities
as their physico-chemical properties. Why, then, should we speak
otherwise of the activities of the substance protoplasm?
“When hydrogen and oxygen are mixed in certain proportions and an
electric spark is passed through them they disappear, and a quantity
of water, equal in weight to the sum of their weights, appears in
their place. There is not the slightest parity between the passive and
active powers of the water and those of the oxygen and hydrogen that
have given rise to it.... We call these and many other phenomena, the
properties of water, and we do not hesitate to believe that in some
way they result from the properties of the component elements of the
water. We do not assume that a something called “aquosity” entered into
and took possession of the oxide of hydrogen as soon as it was formed
and guided the aqueous particles to their places in the facets of the
crystal, or among the leaflets of the hoar frost.”
“Is the case in any way changed when carbonic acid, water, and ammonia
disappear, and in their place, under the influence of pre-existing
protoplasm, an equivalent weight of the matter of life makes its
appearance?”
“It is true that there is no sort of parity between the properties
of the components and the properties of the resultant. But neither
was there in the case of water. It is also true that the influence of
pre-existing protoplasm is something quite unintelligible. But does
anyone quite understand the _modus operandi_ of an electric spark
which traverses a mixture of oxygen and hydrogen? What justification
is there, then, for the assumption of the existence in the living
matter of a something which has no representative or correlative in the
non-living matter which gave rise to it?”
All the investigations of over forty years leave nothing to be added
to this statement of what, in Huxley’s days, was called materialistic
biology. It was a very unpopular statement to make then, but it has
become rather fashionable now. Let the reader compare it with all
that has been spoken and written since 1869, even with the utterances
of the British Association of the year 1912, and he will find that it
expresses the point of view of mechanistic biology far better than
all the subsequent restatements. The only difference he will find is
that the latter have become (as William James has said about academic
philosophies), rather shop-soiled. They have been reached down and
shown so often to the enquiring public, that each display has taken
away something of their freshness.
[Illustration: FIG. 8.]
Now Huxley’s example leads up so well to the consideration of the
differences between the chemical activities of the organism and those
of inorganic matter that we may consider it in some detail. What, then,
_is_ the difference between the explosion of a mixture of oxygen and
hydrogen, and the photo-synthesis of starch by the green plant?
In the case of the synthesis of water we have an example of an
exothermic chemical reaction. We are to think of the mixture of oxygen
and hydrogen as existing in a condition of “false equilibrium.” It may
be compared with a weight resting on an inclined plane.
Suppose that the plane is a sheet of smoothly polished glass, and that
the weight is a smooth block of glass. By canting the plane more and
more an angle will be found at which the slightest push starts the
weight sliding down. Now in the case of the explosive mixture of oxygen
and hydrogen we have a chemical analogue. Either the gases do not
combine at all at the ordinary temperature or they combine “infinitely
slowly.” But the slightest impulse, an electric spark requiring an
almost infinitesimally small quantity of energy, starts the combination
of the gases, and this continues until all is changed into water
vapour. In this reaction a large quantity of energy is liberated in
the form of heat. This heat becomes transformed into the kinetic
energy of the water particles which condense from the steam formed in
the explosion, and these particles assume the temperature of their
surroundings. The energy which was potential in the explosive mixture,
and which was capable of doing work, still exists as the kinetic energy
of the water formed, but it has become unavailable for any natural
process of work.
We have seen what is the general character of the reaction series
in the course of which carbon dioxide and water become starch; and
then this, becoming first soluble, and becoming associated with the
ammonia or nitrate taken into the plant, becomes protoplasm. It is a
reaction which differs from that just described, in that available
energy becomes absorbed and accumulated, and retains the power of doing
work. It is not a reaction which can be initiated by an infinitesimal
stimulus, but one in which just as much energy is required in order
that it may happen as is represented in the energy which becomes
potential in the living substance generated. The first reaction is one
which may take place _by itself_;[17] the other is one which requires
a compensatory energy-transformation in order that it may happen.
In the first reaction energy is dissipated; in the second one it is
accumulated.
[17] It is no use saying that apart from the electric spark the
combination would not take place, for we do not know that the _O_ and
_H_ of the mixture do not combine _very_ slowly, molecule by molecule,
so to speak. At all events there is no functionality between the
infinitesimal quantity of energy supplied by the spark, and the energy
which becomes kinetic in the explosion.
We are thus led to the consideration of the second principle of
energetics and its limitations, but before entering upon this
discussion we must consider the nature of the activities of the
organism.
By the term “metabolism” we understand the totality of the
physico-chemical changes which occur in the living substance of the
organism. In physiological writings we usually find that two categories
of metabolic changes are described: (1) anabolic processes, in the
course of which simple chemical compounds possessing relatively little
energy are built up into much more complex substances, containing a
relatively large quantity of available energy, and therefore capable of
doing work. The transformations constituting an anabolic change must
be accompanied by corresponding compensatory energy-transformations,
to account for the energy which becomes potential in the substances
formed. The formation of starch from carbon dioxide and water, by
the green plant, is such an anabolic change, and the compensatory
energy-transformation is the absorption of radiation from the ether by
the cells of the plant. A further anabolic change in the plant organism
is the formation of amido-substances from the ammonia or nitrate
absorbed from the soil, and from the soluble carbohydrates formed from
the starch manufactured in the green cells.
The typical activities of the chlorophyll-containing organism are of
this nature; they are anabolic. The organism may be a green land-plant;
a marine green, red, or brown alga; a yellow-green diatom, a yellow,
green, red, or brown peridinian or other holophytic protozoan; an
ascidian, mollusc, echinoderm, polyzoan, worm, or coral containing
“symbiotic algæ” (that is the chlorophyll-containing cells of some
plant organism which have become associated with the animal and
incorporated in its tissues). In all these cases the presence of
this chlorophyllian substance confers on the organism the power of
effecting the compensatory energy-transformation, by the aid of
which carbon dioxide and water are built up into starch. What this
transformation is, and what are the steps by which the carbon dioxide
and water become carbohydrate we do not exactly know. Solar radiation
impinging upon an inorganic substance is partly reflected and partly
absorbed. The absorbed fraction may become transformed in such a way
as to render the substance phosphorescent, or it may transform into
chemical energy, as when light impinges on a photographic plate, but
as a general rule it is transformed into heat. In the green plant,
however, the transformation of radiation into heat does not occur--at
least the heating is very small--and it passes directly or indirectly
into the potential chemical energy of the starch which is synthesised.
We must regard this power of absorbing radiation and utilising it in
compensatory transformations as a general character of protoplasm.
It is true that it is now specialised in the cells containing the
chlorophyll bodies, but there are indications that it may be present in
the tissues of the animal devoid of chlorophyll.
Other anabolic transformations occur in the animal. The food-stuffs
which are absorbed from the intestine are substances which have
undergone dissociations, the nature of which is such as to render them
capable of absorption and of reconstruction. These anabolic changes in
the higher animal are exceptional, and their usefulness lies in the
fact that by their means substances become capable of being transported
by the tissue fluids of the body.
(2) Katabolic changes in the animal body correspond in their frequency
of occurrence to the anabolic changes of the plant organism. In them
complex chemical substances undergo transformation into relatively
simple substances, and the contained energy at the same time undergoes
a parallel transformation, passing into the form of heat and mechanical
energy, while a fraction becomes dissipated. Food-stuffs taken into the
alimentary canal break down in this way, but to a very limited extent.
Proteids undergo dissociation or decomposition into amido-substances,
while fats are dissociated into fatty acids and glycerine.
Doubtless energy is dissipated in these processes, serving no other
purpose but to heat the contents of the alimentary canal, but this
energy-transformation has not been worked out very completely and it
is a question whether, given a healthy animal and perfect food-stuffs,
any energy would necessarily be lost during the digestive processes.
The reactions involved in the latter do not belong to the category
of chemical changes proceeding from the complex to the simple, with
a liberation of energy; but appear to involve rather a rearrangement
of the constituents of a complex molecule, a process in which the
contained energy need not undergo change in quantity. These processes
involve the action of _enzymes_.
Enzymes play a great part in modern physiological theory and we must
consider them in detail. Let us attach a concrete meaning to the
general notion of enzyme-activity by considering the phenomena known
as _catalysis_. The metal platinum can be brought into a very fine
stage of division when it is known as platinum black. In this condition
it brings about reactions in chemical mixtures or substances which
would not otherwise occur: a mixture of oxygen and hydrogen explodes
when brought in contact with platinum black, and a mixture of coal
gas and air inflames, a reaction which is made use of in the little
gas-lighting apparatus which most people have seen. If, again, a
powerful electric current be passed between platinum wires which are
a little distance apart, and are immersed in water, the metal becomes
torn away from the points of the wire in the form of an impalpable
powder, colloidal platinum. The liquid containing this colloid then has
the power of setting up chemical changes in other substances, changes
which would not otherwise occur, or, at least, would occur very slowly.
In general such catalysts, platinum black or colloidal platinum for
instance, have the following characters: (1) a small quantity is
sufficient to cause change in a large (theoretically an infinite)
quantity of the substance acted upon; (2) the nature and quantity
of the catalyst remain at the end the same, as at the beginning of
the reaction; (3) a catalyst does not start a reaction in any other
substance or substances, it can only influence the rate at which
this reaction may occur: apparently it does, in some cases, start a
reaction, but in such cases we suppose that the latter proceeds so
slowly as to be imperceptible; (4) the final state of the reaction
is not affected by the catalyst; it depends only on the nature of
the interacting substance or substances; (5) the final state is not
affected either by the nature or quantity of the catalyst: it is the
same if we employ different catalysts, or a large or small quantity of
the same catalyst. Finally, it appears that the phenomena of catalysis
are universal: “There is probably no kind of chemical reaction,” says
Ostwald, “which cannot be influenced catalytically, and there is no
substance, element, or compound which cannot act as a catalyser.”[18]
[18] A statement of interest in view of the enormous number of
“ferments” or enzymes discovered by physiologists. It would appear that
any tissue in any organism is capable of yielding an enzyme to modern
investigation.
Enzymes, then, are agents which are produced by the organism, and which
act by influencing (accelerating or retarding) chemical reactions.
An enzyme, as such, need not exist in a tissue; it is there as a
_zymogen_, a substance which may become an enzyme when required. An
enzyme need not be active: it may be necessary that it should be
“activated” by a _kinase_, another substance produced at the same time.
Associated with many enzymes are _anti-enzymes_, substances which undo
what their corresponding enzymes have done. Finally some, perhaps
most, enzymes are reversible, that is, if they produce a change in a
certain substance they can also produce the opposite kind of change:
the meaning of this will become clearer a little later on. We have
spoken of enzymes as “agents” or “substances,” but it is not at all
certain that they are definite chemical compounds. In the preparation
of an enzyme what the bio-chemist obtains is a liquid, a glycerine
or other extract _which possesses catalytic properties_. An actual
catalytic substance, like platinum black, cannot be obtained from
this liquid. A white powder may be obtained, but this usually proves
to be proteid in composition; it is not the actual enzyme itself but
is the impurity associated with the latter. Now the very great number
of enzymes “isolated” by the physiologists has rather destroyed the
original simplicity of the idea of enzyme activity and suggests a
parallel statement to that made by Ostwald about catalysts: any tissue
substance may influence the reactions that may possibly occur in other
tissue substances. But while pure chemistry has to deal with definitely
known chemical compounds in the phenomena of catalysis, this cannot be
said to be the case with physiology in dealing with enzymes. Reasoning
by analogy, we may say that it is probable that enzymes are definite
proteids, or chemical substances allied to these, but this has not been
clearly demonstrated, and it is possible that the phenomena of enzyme
activity may belong to some other category of energy-transformations.
However this may be, the conception is a useful one in describing the
reactions of the organism, and it may be illustrated by considering the
digestion and absorption of fat in the mammalian intestine, a process
which appears to be better known than that of proteid digestion. A
neutral fat consists of an acid radicle, oleic, palmitic or stearic
acids, for instance, united with glycerine. The action of the
pancreatic or intestinal enzymes is to dissociate this fatty salt. Let
us write the formula of the latter as _G F_, _G_ being the glycerine
base, and _F_ the fatty acid; then
_G F_ ⇄ _G_ + _F_
which means that the enzyme can cause the neutral fat to dissociate
into glycerine and fatty acid. This action will go on until a state of
equilibrium is attained, in which there is a certain quantity of each
of the radicles, and a certain quantity of unchanged neutral fat, the
ratio of all these to each other depending on various things. When
this state of equilibrium is attained the enzyme does indeed go on
splitting up more neutral fat, but it is a _reversible_ enzyme, and it
also causes the glycerine and fatty acid already split up to recombine,
forming neutral fat. A condition is, therefore, reached in which the
composition of the mixture remains constant.
Now there is dissociated fat in the intestine after a meal, but there
is only neutral fat in the wall of the intestine. The fat itself cannot
pass through the cells forming the intestinal wall, but the glycerine
and fatty acid into which it is dissociated can so pass, since they are
soluble in the liquids of the intestine. We suppose that the cells of
the wall of the intestine also contain the fat-splitting ferment; this
ferment in the cells acts on the glycerine and fatty acid immediately
they enter and recombines these radicles again into neutral fat, the
above equation now reading from right to left. But after a time this
reaction in the cells will also begin to reverse, for the enzyme
will begin to split up the synthesised neutral fat when the state of
chemical equilibrium in the new conditions is attained. Fatty acid
and glycerine will then diffuse out from the cells into the adjacent
lymph stream or blood stream--perhaps neutral fat will also pass from
the cells into these liquids, we are not sure. At all events the lymph
and blood after a meal containing much fat are crowded with minute fat
globules. But why are there no fatty acids or glycerine in the blood,
for the latter also contains lipase (the fat-splitting enzyme)? The
explanation is, apparently, that either an anti-enzyme is produced, or
that the enzyme passes into a _zymoid_ condition. Why also does fat
accumulate in the tissues? Here, again, the activity of the enzyme,
which from other considerations we may regard as being universally
present almost everywhere in the body, must be supposed to be arrested
by some means.
The conception of a catalytic agent, such as we can study in pure
chemistry, thus carries us a long way in our description of the
processes of digestion, absorption, and assimilation. We have applied
it to the case of fat-digestion, but very much the same general scheme
might also apply to many other processes in the body. Obviously it
enables us to describe these processes in terms of physico-chemical
reactions, but we cannot fail to see that ultimately we are compelled
to assume the existence of reactions which were not included in the
original conception--the activation of the enzyme at the proper moment
by the kinase, the operation of the anti-enzyme, and the passage of the
enzyme into the zymoid. Just why these things happen as they do we do
not know, yet the whole problem becomes shifted on to these reactions.
In the same way we apply the purely physical processes of the osmosis
and diffusion of liquids to the circulation of substances in the animal
body. The nature of these processes will probably be familiar to the
reader, nevertheless it may be useful to remind him that by diffusion
we understand the passage of a liquid, containing some substance in
solution, through a membrane; and by osmosis the passage of a solvent
(but not of the substance dissolved in it) through a “semi-permeable
membrane.” The molecules of the solvent (water, for instance) pass
through the membrane (the wall of a capillary, or lymphatic vessel),
but the molecules of the substance (salt, for instance) dissolved in
the solvent do not pass. Let us suppose that a strong solution of
common salt in water is injected into the blood stream: what happens
is that osmosis takes place, the water in the surrounding lymph spaces
passing into the blood stream because the concentration of salt there
is greater than it is in the lymph. While this is happening, the
capillary walls are acting as semi-permeable membranes, allowing the
molecules of water to pass through but not the molecules of salt.
Very soon, however, the process of osmosis becomes succeeded by one of
diffusion, and the salt molecules pass through the capillary wall into
the lymph and are excreted.
[Illustration: FIG. 9.]
Undoubtedly the purely physical processes of diffusion and
osmosis occur all over the animal body and are the means whereby
food-materials, secretory, and excretory substances are transported
from blood to lymph, or _vice versa_, from lymph to cell substance or
to glandular cavities, and so on. But it is also the case that in very
many processes the activity of the cells themselves plays an important
part. It may even be the case that a particular process, after all
physical agencies are taken into account, reduces down to this action
of the cells. To understand this we must consider the mode of working
of some well-known organ, and the best possible example of such an
organ, considered as a mechanism, is that of the sub-maxillary salivary
gland of the mammal.
What, then, is this mechanism and how does it act? The gland is a
compound tubular one, its internal cavity being prolonged into the duct
which opens into the mouth. The saliva prepared in the gland issues
from this duct. Blood is carried to the gland by twigs of the facial
artery, and, after circulating through it, is carried away by factors
of the jugular vein. Two nerves supply the gland: one is the chorda
tympani, a branch of a cranial nerve, and the other is a sympathetic
nerve. Lymph also leaves the gland by a little vessel.
Now suppose we have laid bare all this mechanism in a living animal and
make experiments upon it. If we stimulate the chorda tympani there is a
copious flow of thin watery saliva, but if we stimulate the sympathetic
there is a less copious flow of thick viscid saliva. Why is this? We
find on closer analysis that the chorda contains fibres which dilate
the small arteries so that there is an increased flow of blood through
the gland; but that, on the other hand, the sympathetic contains fibres
which constrict the arteries, thus leading to a reduced flow of blood.
This accounts for the fact that “chorda-saliva” is abundant and thin,
while “sympathetic-saliva” is scarce and thick. It was thought at one
time that the chorda contained fibres which stimulated the gland to
produce watery saliva, while the sympathetic contained fibres which
stimulated it to produce mucid saliva. This, however, is not the case.
Both nerves contain the same kind of secretory fibres: their other
fibres differ mainly in that they act differently on the arteries.
It might be the case--indeed it was at one time thought that it was the
case--that secretion of saliva was simply a matter of blood-flow: an
abundant arterial circulation gave rise to abundant saliva, a sparse
flow to a sparse saliva. Undoubtedly the secretion depends on blood
supply, but not _solely_. If it did, then the whole process might be
conceived to be a very simple mechanical one--filtration or diffusion
of the saliva from the blood stream through the thin walls of the blood
vessels, and the walls of the tubules into the cavity of the gland.
If this were the case, then the liquid in the gland would be the same
in composition and concentration as the liquid part of the blood--the
plasma. But it is really different in composition and it is not so
concentrated. Now osmotic pressure--on the action of which so much is
based--cannot help us, for the liquid in the gland is less concentrated
than that in the blood vessels, so that water ought to pass from gland
to blood instead of from blood into gland. Again, if we tie the duct,
so that the saliva cannot escape, secretion still goes on, though
the hydrostatic pressure of saliva in the cavity of the gland may be
considerably greater than that of the liquid in the blood vessels. Yet
again, if we stop the blood flow by tying the artery, secretion of
saliva may still go on for a time.
Therefore the only physical agencies we can think of do not explain the
secretion. The latter is actually the work of the individual cells,
stimulated by the nerves. If the volume of the gland be measured
just while it is being stimulated to secrete, it will be found that
the organ becomes _smaller_, yet while it is being stimulated the
blood-vessels are being dilated so that the volume of the whole
structure ought to become greater. Obviously part of the substance of
the gland is being emptied out through its duct as the secretion.
If we examine the cells of the gland in various states we see clearly
that granules of some material, different in nature from the substance
of the protoplasm itself, are being formed within them. Evidently these
granules swell up during secretion and discharge their contents into
the ducts. Further changes in the characters of the cell-substance,
and in the nucleus, can be observed, and all these indicate that the
protoplasm of the cells, as the result of stimulation, elaborates
certain substances; that these substances are then washed out, so
to speak, into the duct by the withdrawal of water from the cell;
and that thereafter the cell absorbs fresh nutritive material from
the lymph which exudes from the blood vessels, along with water.
The distinctive part of the whole train of processes is, then, this
elaboration of material by the cells themselves; while the concomitant
changes in the calibre of the blood vessels and in the flow of blood
and lymph are subsidiary ones. In the process of secretion of saliva
energy is absorbed from the chemical substances of the blood to bring
about the passage of water from a region of high to a region of low
osmotic pressure; oxygen and nitrogen, with other elements of course,
are withdrawn from the arterial blood stream for the purpose of the
secretion, and carbon dioxide and other substances are given off to the
venous blood and lymph.
The problem thus is pushed back from the mechanical events occurring
in the nervous and circulatory processes, to the physico-chemical ones
occurring in the cells of the gland tubules; and it thus becomes much
more obscure. It is true that we can formulate a hypothesis which
describes, in a kind of way, these intra-cellular metabolic changes,
in terms of physico-chemical reactions, and, without doubt, reactions
of this kind must occur within the cell. But if we could test any such
hypothesis as easily as the mechanical ones suggested, should we find
it any more self-sufficient?[19]
[19] We have not referred to “psychical secretion.” If we smell some
very savoury substance our “mouth waters,” that is, secretion of
saliva occurs. If we even see some such substance the same secretion
occurs. All this is clear and can be “explained” mechanistically: the
stimulation of the olfactory or visual organs begins a kind of reflex
process. But if we even _think_ about some very savoury morsel saliva
may be secreted. We must suppose now that our consciousness, something
which has nothing to do, it must be noted, with energy-changes in the
body, can react on the body. If we show a dog an attractive bone it
will secrete saliva; if we show it again and again, the same thing
occurs. But after certain such trials the dog will realise that he is
being played with, and the exhibition of the bone no longer evokes a
flow of secretion. Why is this? The whole process has now become more
mysterious than ever.
Irritability and contractility are general properties of the organism.
These properties are illustrated by the irritability of an _Amœba_
or _Paramœcium_ to stimuli of many kinds; by the movements of the
pseudopodia of the former animal, or of the cilia of the latter; by
the nervous irritability of the higher animal, and the contraction of
its muscles when they are stimulated. They are among the fundamental
properties or functions of living protoplasm, and their study is of
paramount interest, and carries us to the very centre of the problem
of the activities of the organism. Naturally physiologists have never
ceased to attempt to describe irritability and contractility in terms
of physics, but though we may be quite certain that the things that do
occur in these phenomena are controlled physico-chemical reactions, it
must be remembered that what we positively know about their precise
nature is exceedingly little.
What is the nature of a nervous impulse? When a receptor organ is
stimulated, as, for instance, when light impinges on the cone cells
of the retina, or when the nerve-endings in a “heat-spot” in the skin
are warmed, or when the wires conveying an electric current are laid
on a naked nerve, an impulse is set up in the nerve proceeding from
the place stimulated, and we must suppose that approximately the same
amount of energy moves along the nerve as was communicated to the
receptor or the nerve itself by a stimulus of minimal strength. How
does it so move? Several facts of capital importance result from the
experimental work. (1) The impulse travels with a velocity variable
within certain limits, say from 8 to 30 metres per second; (2) it
travels faster if the temperature is raised (up to a certain limit);
(3) it is difficult to demonstrate that the passage of this impulse is
accompanied by definite chemical changes in the nerve substance: it
is stated that carbon dioxide is produced, but this is not certainly
proved; (4) an electric current is produced in the nerve as the result
of stimulation; (5) no heat is produced, or at least the rise of
temperature, if it occurs, is less than 0.0002° C.
Thus it is quite certain that physical changes accompany the
propagation of the nerve-impulse, for the latter has a certain
velocity, which depends on the temperature, and an electric change
also occurs in the substance of the nerve. Is this electric change
the actual nerve impulse? It is hardly likely, since the velocity
of the impulse is very much less than that of the propagation of an
electric change through a conductor; besides, the passage of the
impulse is not accompanied by a measurable heat evolution, although
the flow of electricity along a poor conductor must generate heat
and dissipate energy. Is it a chemical change? Then we should be
able to observe metabolism in the nerve substance--that is if the
energy-change is a thermodynamic one--while it is not at all certain
that metabolic changes do occur. Nevertheless it seems probable that
a physico-chemical change is actually propagated when we consider
the chemical specialisation of the substance of the axis-cylinder of
the nerve. Now the velocity of propagation of the nervous impulse
is of the same order of magnitude as that of an explosive change in
chemical substances (using the term “explosion” to connote chemical
disintegrations rather than combustions). If we imagine a long rod of
dynamite, or picric acid, or a long strand of loosely-packed gun-cotton
to be exploded by percussion at one end, then a transmission of the
chemical disintegration of any of these substances will pass along
the rod, etc., with a velocity which will certainly vary with the
physical condition of the material. It would be a high velocity in
a rod of dynamite, or fused picric acid, but a lower velocity in a
loosely aggregated strand of gun-cotton, or a trail of picric acid
powder. Is this what happens in the nerve when an impulse travels
along it? Obviously not, since the substance of the nerve is not
altered appreciably, while that of the explosive substance passes into
other chemical phases. We might imagine, then, such a change in the
nerve fibrils as that of a reversible transformation of some chemical
constituent:--
(2) (1)
-------------------------------------------------------------
: _a_ + _b_ : _a_ + _b_ : _a_ + _b_ : _a_ + _b_ : _a_ + _b_ :
: ⇣⇡ : ⇡⇣ : ⇡⇣ : ⇡⇣ : ⇡⇣ :
: _c_ + _d_ : _c_ + _d_ : _c_ + _d_ : _c_ + _d_ : _c_ + _d_ :
-------------------------------------------------------------
Let us imagine the substance of the fibril to be composed of, or at
least to contain, the substances _a_ + _b_ which dissociate reversibly
into the substances _c_ + _d_. At any moment, and in any particular
physical state, as much of _a_ and _b_ pass into _c_ and _d_ as _c_
and _d_ pass into _a_ and _b_. There will be equilibrium. But now let
a stimulus alter the physical conditions: prior to the stimulus the
phase was _a_↓{m} + _b_↓{n} = _c_↓{p} + _d_↓{r}--the suffixes _m_, _n_,
_p_, _r_, denoting the concentrations of _a_, _b_, _c_, and _d_--but
after the stimulus the phase may be _a_↓{m1} + _b_↓{n1} = _c_↓{p1} +
_d_↓{r1}. Now the element of the nerve substance (1) forms a system
with the element (2). The condition in (2) is _a_↓{m} + _b_↓{n} =
_c_↓{p} + _d_↓{r}, and that of (1) _a_↓{m1} + _b_↓{n1} = _c_↓{p1}
+ _d_↓{r1}, but these two together now fall into a new state of
equilibrium and this is transmitted along the whole nerve-fibril with
a velocity which belongs to the order of magnitude of that of chemical
changes. If the stimulus remains constant (a constant electric current
for instance), the new condition of equilibrium will be established
throughout the whole length of the fibril and the nervous impulse will
be a momentary one (as it is in this case). But if the stimulus is an
intermittent one (an interrupted electric current, light-vibration,
sound-vibrations), then in the intervals the former condition of
equilibrium will become re-established and the nervous impulse will
be intermittent (as it is). There would be no work done on the whole
in the changes, except that done by the transmission of the changed
state of equilibrium to the substance of the effector organ in which
the nerve-fibril terminates--the substance of a muscle fibre, or the
cell of a secretory gland, for instances. There would, probably, be a
certain dissipation of energy as in the case of the propagation of an
electric impulse through a poor conductor, but all our knowledge of the
chemistry of the nerve fibre points to this amount of dissipation as
tending to vanish.
Something analogous to this may be expected to take place in a muscle
fibre when it contracts; except that, of course, energy is transformed
in this case. What precisely does happen we do not know and at the
present time no physico-chemical hypothesis of the nature of muscular
contraction exactly describes all that can be observed to take place.
Certain positive results have, of course, been obtained by chemical
and physical investigation of the contracting muscle: carbon dioxide
is given off to the lymph and blood stream, and the amount of this is
increased when an increased amount of work is done by the muscle; heat
is produced and this too increases with the work performed; glycogen
is used up, and lactic acid is produced; finally oxygen is required,
and more oxygen is required by an actively contracting muscle than
by a quiescent one. Now the obvious hypothesis correlating all these
facts is that the muscle substance is oxidised, and that the heat so
produced is transformed into mechanical energy. “We must assume,” says
a recent book on physiology, “that there is some mechanism in the
muscle by means of which the energy liberated during the mechanical
change is utilised in causing movement, somewhat in the same way as the
heat energy developed in a gas-engine is converted by a mechanism into
mechanical movement.”
Now, must we assume anything of the kind? To begin with, life goes
on, and mechanical energy is produced in many organisms living in a
medium which contains no oxygen. Anaerobic organisms are fairly well
known, and we cannot suppose that in them energy is generated by
the combustion of tissue substance in the inspired oxygen. A muscle
removed from a cold-blooded animal will continue to contract in an
atmosphere containing no oxygen, and it will continue to produce
carbon dioxide. It is true that the contractions soon cease, even
after continued stimulation under conditions excluding the fatigue
of the muscle, but do the contractions cease _because_ the oxygen
supply is cut off, or because the muscle dies in these conditions?
We know that some complex chemical substance is disintegrated during
contraction and that mechanical energy and heat are produced and that
carbon dioxide is also produced. We know that the carbon contained in
the latter gas corresponds roughly with the carbon contained in the
muscle substance which undergoes disintegration, but does all this
justify us in saying that this substance is oxidised in order that its
potential chemical energy may be transformed into mechanical energy?
Obviously not, since we might equally well suppose that the complex
metabolic substance of the muscle splits down into simpler substances
and that in this transformation energy is generated. Suppose that these
simpler substances are poisonous and that they must be removed as
rapidly as formed. The rôle of the oxygen may be to oxidise them, thus
transforming them into carbon dioxide, an innocuous substance which
can be carried away quickly in the blood stream. This line of thought,
according to which the rôle of oxygen is an anti-poisonous one, is
held at the present day by some physiologists, and many considerations
appear to support it; the existence of “oxidases,” for instance,
enzymes which produce oxidations which would not otherwise occur in
their absence. Such enzymes exist in very many tissues, and they may,
apparently, be present in an inactive form, requiring the agency of a
“kinase” before they are able to act.
The usual view among physiologists is that the muscle fibre is a
thermodynamic apparatus transforming the heat generated during
metabolism into mechanical energy. How is this transformation effected?
It cannot be said that we have any one hypothesis more convincing than
another. It has been suggested that alterations of surface tension
play a part, or that the heat produced by oxidation causes the fibre
to imbibe water and shorten. Engelmann has devised an artificial
muscle consisting of a catgut string and an electrical current passing
through a coil of wire, and by means of this he has reproduced the
phenomena of simple contraction and tetanus. But it remains for future
investigation to verify any one of these hypotheses.
When Huxley published his _Physical Basis of Life_, probably few
physiologists had any doubt that protoplasm was a definite chemical
substance, differing from other organic substances only by its much
greater complexity. But in 1880 Reinke and Rodewald published the
results of an analysis of the substance of a plant protoplasm and these
appear to have demonstrated that the substance was really a mixture
of a number of true chemical compounds and was not a single definite
one. Now all of these substances might exist apart from protoplasm, and
in the lifeless form, and a simple mixture of them could hardly bring
forth vital reactions. These results were followed by the morphological
study of the cell--the discovery of the architecture of the nucleus,
and so on, and so opinion began to turn to the hypothesis that the
vital manifestations of protoplasm were the result of its _structure_.
Microscopical examination of the cell appeared to disclose a definite
arrangement, the “foam” or “froth” of Butschli, for instance. But,
again, it was easily shown that the foam, or alveolar structure of
protoplasm was merely the expression of physical differences in the
substances composing the cell-stuff--they reduced to phenomena of
surface tension and the like. Artificial protoplasm and artificial
_Amœbæ_ were made--at least mixtures of olive oil and various other
substances were made which simulated many of the phenomena of
protoplasm in much the same way as crystalline products may be made
which simulate the growth of a plant stem with its branches. For
instance, one has only to shake up a little soapy water in a flask
to see what resembles surprisingly the arrangement of certain kinds
of connective tissues in the organism. Obviously these artificial
phenomena have nothing to do with living substance.
Yet if we grind up a living muscle with some sand in a mortar we do
destroy something. The muscle could be made to contract, but after
disintegration this power is lost. We have certainly destroyed a
structure, or mechanism, of some kind. But, again, the paste of muscle
substance and sand still possesses some kind of vital activity,
for with certain precautions it can be made to exhibit many of the
phenomena of enzyme activity displayed by the intact muscle fibres,
or even the entire organism. Mechanical disintegration, therefore,
abolishes some of the activities of the organism, but not all of them.
If, however, we heat the muscle paste above a certain temperature, the
residue of vital phenomena exhibited by it are irreversibly removed,
so that heating destroys the mechanism. This we can hardly imagine
to be the case (within ordinary limits of temperature at least) with
a physical mechanism, but again a mechanism which is partly chemical
might be so destroyed. We see, then, that protoplasm possesses a
mechanical structure, but that all of its vital activities do not
necessarily depend on this structure. The full manifestation of these
activities depends on the protoplasmic substance possessing a certain
volume or mass, and also on a certain chemical structure.
If living protoplasm has a structure, and is not simply a mixture of
chemical compounds, what is it then? Two or three physico-chemical
concepts are at the present time very much in evidence in this
connection. When the substances known as _colloids_ were fully
investigated by the chemists, much attention was paid to them by the
physiologists, so that life was called “the chemistry of the colloids,”
just as after the investigation of the enzymes it was called the
“chemistry of the enzymes,” and when the discovery of the relative
abundance of phosphorus in cell-nuclei and in the brain was discovered,
it was called the “chemistry of phosphorus.” Colloids (_e.g._ glue)
are substances that do not readily diffuse through certain membranes,
in opposition to crystalloids (_e.g._ solution of common salt) which
do readily so diffuse. They form solutions which easily gelatinise
reversibly, that is, can become liquid again (glue); or coagulate
irreversibly, that is, cannot become liquid again (albumen); which have
no definite saturation point; which have a low osmotic pressure (and
derived properties), etc.; and the molecules of which are compound
ones consisting of combinations of the molecules of the substance with
the molecules of the solvent, or with each other, that is, they are
molecular aggregates.
Colloids pass insensibly into crystalloids on the one hand and into
coarse suspensions (water shaken up with fine mud, for instance)
on the other. We may replace the concept of a colloid by those of
“suspensoids” and “emulsoids.” A suspensoid is a liquid containing
particles in a fine state of division--if the division is that into
the separate molecules we have a solution, if into large aggregates
of molecules we have a suspension. If the substance in the liquid is
itself liquid, the whole is called an emulsoid. On the one hand this
approaches to a mixture of oil in soap and water--an emulsion--and
on the other hand to such a mixture as chloroform shaken up with
water, when the drops of chloroform readily join together so that two
layers of liquid (chloroform and water) form. What we see, then, in
protoplasm is a viscid substance possessing a structure of some kind,
and containing specialised protoplasmic bodies in its mass (nuclei,
nucleoli, granules of various kinds, chlorophyll, and other plastids,
etc.). It may contain or exhibit suspensoid or emulsoid parts or
substances, or it may contain truly crystalloid solutions. These phases
of its constituents are not fixed, but pass into each other during
its activity. Nothing that we know about it justifies us in speaking
about a “living chemical substance.” On analysis we find that it is a
mixture of true chemical substances rather than a substance. It is no
use saying that in order to analyse it we must kill it, for what we can
observe in it without destroying its structure or activities indicates
that it is chemically heterogeneous.
This is not a textbook of general physiology, and the examples of
physico-chemical reactions in the organism which we have selected have
been quoted in order to show to what extent the chemical and physical
methods applied by the physiologists have succeeded in resolving the
activities of the organism. The question for our consideration is this:
do these results of physico-chemical analysis fully describe organic
functioning? Dogmatic mechanism says “yes” without equivocation.
Now it is clear, from even the few typical examples that we have
quoted, that physiological analysis shows, indeed, a resolution of
the activities of the organism into chemical and physical reactions.
How could it do otherwise? How could chemical and physical methods of
investigation yield anything else than chemical and physical results?
The fact that these methods _can_ be applied to the study of the
organism with consistent results shows that their application is
valid; that we are justified in seeing physico-chemical activities in
life. But are these results _all_ that we have reason to expect?
We turn now to Bergson’s fertile comparison of the physiological
analysis of the organism with the action of a cinematograph. If we
take a series of photographic snapshots of, _e.g._, a trotting horse
and then superpose these pictures upon each other, we produce all the
semblance of the co-ordinated motions of the limbs of the animal. Yet
all that is contained in the simulated motion is immobility. From a
succession of static conditions we appear to produce a flux. Yet if we
could contract our duration of, _e.g._, a week, into that corresponding
to five minutes--if we could speed up our perceptual activity--should
we not see the cinematographic pictures as they really are--a series
of immovable postures and nothing more: truly an illusion? If, again,
we reverse the direction of motion of the film, we integrate our
snapshots into something which is absolutely different from the reality
which they at first represented; and by such devices the illusions and
paradoxical effects of the picture-house farces are made possible.
Well, then, in the physiological analysis of the activity of the
organism do we not do something very analogous to this? The complexity
of even the simplest function of the animal is such that we can only
attend to one or two aspects of it at once, arbitrarily neglecting all
the rest. We find that the hydrostatic pressure of blood, and lymph,
and secretion, the osmotic pressure, the diffusibility, vaso-motor
actions, and other things must be investigated when considering the
question of how the submaxillary gland secretes saliva. One, or as many
as possible, of these reactions are investigated at one time, and then
the results are pieced together--integrated--in order to reproduce the
full activity of the whole indivisible process. But in doing this do we
not introduce something new--a _direction_ or order of happening--into
the elements of the dissociated activity of the organism? Each
elemental process must occur at just the right time.
What right have we to say that the activity of the organism is _made
up_ of physico-chemical elements? Just as much as we have in saying
that a curve is made up of infinitesimal straight lines. Let us adopt
Bergson’s illustration, with a non-essential modification.
[Illustration: FIG. 10.]
The curve 1–8 is a line which we draw freehand with a single
indivisible motion of the hand and arm and eye. It is something unique
and individualised, in that no other curve ever drawn, in a similar
manner, exactly resembles it. Let us investigate it mathematically. We
can select very small portions of it--elements we may call them--and
each of these elements, if it is small enough does not differ
_sensibly_ from a straight line. Let us produce each of these straight
lines in both directions, it is then a tangent to the curve, and it
does actually coincide with the curve at one mathematical point--the
points 1–8 in the figure. The tangent then has _something in common
with the curve_, but would a series of infinitesimally small tangents
reproduce the curve? Obviously not, for the equations of the tangents
would have the form _ax_ + _b_, while that of the curve itself would be
quite different, containing _x_ as powers of _x_, or as transcendental
functions of _x_. In this investigation what we succeed in obtaining
are the derivatives of the curve, and to reproduce the latter from
its elements we have to integrate the derivatives; that is, another
operation differing in kind from our analytical one must be performed.
Now in this illustration we have doubtless something more than an
analogy with our physico-chemical analysis of life. The activities of
the organism do reduce to bio-chemical ones (the elemental straight
lines on the curve), and each of these reactions has something in
common with life (it is tangent to life, touching it at one point).
But if we attempt to reconstitute life from its physico-chemical
derivatives we must integrate the latter, and in doing so we over-pass
the bounds of physics, just as integrating a mathematical function we
necessarily introduce the concept of the “infinitely small.”
The physico-chemical reactions into which we dissociate any vital
function of the organism have, then, each of them, something in common
with the vital function. But their mere sum is not the function.
To reproduce the latter we have to effect a co-ordination and give
directions to these reactions. In all physiological investigations
we proceed a certain length with perfect success; thus the elements,
so to speak, of the function of the secretion of saliva are (1)
the blood-pressure, (2) the hydrostatic pressure of the secretion
in the lumina of the gland tubules, (3) the diffusibility of the
substances dissolved in the blood and lymph through the walls of these
vessels, (4) the osmotic pressure of the same substances, and (5)
the stimulation of the gland cells by “secretory nerve fires.” Now
the investigations carried out--and no part of the physiology of the
mammal has been so patiently studied as the salivary gland--fail, so
far, completely to describe the function in terms of these elements.
In the end we have to refer the secretion to intra-cellular processes,
and then we begin to invoke again processes of osmotic pressure,
diffusibility, and so on with reference to the formation of the drops
of secretion which we can see formed in the gland cells. We are forced
to the formulation of a logical hypothesis as to the nature of these
intra-cellular processes, and since much that goes on in the cell
substance is, so far, beyond physico-chemical investigation, our
hypothesis will be as difficult to disprove as to verify.
* * * * *
Let us return now to Huxley’s comparison of the activity of the green
plant with the chemical reaction which occurs when an electric spark
is passed through a mixture of oxygen and hydrogen. The lecture on the
“Physical Basis of Life” was published in 1869; in 1852 William Thomson
published his paper “On a Universal Tendency of Nature to Dissipation
of Energy,” and a year or two before that Clausius had applied Carnot’s
law to the kinetic theory of heat: the second principle of energetics
had therefore even then been exactly formulated, but its significance
for biological speculation had not been recognised by Huxley, any
more than it has generally been recognised by most biologists since
1869. What, then, does the comparison of Huxley show? Clearly that the
physical changes which occur in the explosion of a mixture of oxygen
and hydrogen _trend_ in a different direction from those which occur in
the photo-synthesis of starch by a green plant. Generally speaking,
chemical activity, that is, the possibility of occurrence of chemical
reactions, is a case of the second law of energetics. Energy passes
from a state of high to a state of low potential. A chemical reaction
will occur if this change of potential is possible.
In all such changes energy is dissipated. What exactly does this mean?
It means that, generally speaking, the potential energy of chemical
compounds tends to transform into kinetic energy; while differences
in the intensity factor of the kinetic energy of the bodies forming
a system tend to become minimal. In a mixture of oxygen and hydrogen
there is energy of two kinds, (1) potential energy due to the position
of the molecules (O and H molecules are separated); and (2) kinetic
energy of the molecules (which are moving about in the masses of gas).
After the explosion the potential energy acquired in the separation of
the molecules of O and H has disappeared (the molecules having combined
to form water), but the kinetic energy has greatly increased, since the
explosion results in the formation of steam at high temperature. But
now this steam radiates off heat to adjacent bodies, or becomes cooled
by direct contact with the envelope which contains it. The energy of
the explosion is therefore distributed to the adjoining bodies, and
the temperature of the latter becomes raised. But these again radiate
and conduct heat to other bodies, and in this way the heat generated
becomes indefinitely diffused.
The general effect of all physico-chemical changes is therefore the
generation of heat, and then this heat tends to distribute itself
throughout the whole system of bodies in which the physico-chemical
changes occur. The energy passes into the state of kinetic energy,
that is, the motion of the molecules of the bodies to which the heat
is communicated. This molecular motion is least in solids, greater in
liquids, and greatest in gases. If solids, liquids, and gases are in
contact, forming complex systems, the kinetic energy of their molecules
becomes distributed in definite ways, depending on the constants of
the systems. After this redistribution the kinetic energy of these
molecules is unavailable for further energy transformations, so that
phenomena or change in the system ceases. There is no longer effective
physical diversity among the parts of the system.
We find that this conception of dissipation of energy cannot be applied
to the organism, at least not with the generality in which it applies
to physical systems. Why? Not because the conception is unsound, or
because the physico-chemical reactions that occur in material of the
organism are of a different order from those that occur in inorganic
systems--they are of the same order. The second law of energetics is
subject to limitations, and it is because it is applied to organic
happenings without regard to these limitations that it does not
describe the activities of the organism as well as it describes those
of inorganic nature.
What, then, are these limitations? We note in the first place that
the laws of thermodynamics apply to bodies of a certain range of
size; or at least the possibility of mathematical investigation (on
which, of course, all depends) is limited to “differential elements”
of mass, energy, and time. We cannot apply mathematical analysis to
bodies, or time-intervals of “finite size,” since the methods of the
differential and integral calculus would not strictly be applicable.
But molecules are so small (1 cubic centimetre of a gas may contain
about 5.4 × 10^{19} of them) that even such a minute part of a body, or
liquid, or gas as approximates to the infinitesimally small dimensions
required by the calculus, contains an enormous number of molecules.
Obviously we cannot investigate the individual molecules. Even if
experimental methods could be so applied, such concepts as density,
pressure, volume, or temperature would have no meaning. Physics, then,
is based on collections of molecules, and the properties of a body are
not those of a molecule of the same body. Such concepts as temperature
and pressure are _statistical_ ones, and are applied to the mean
properties of a large number of molecules.
[Illustration: FIG. 11.]
We can best illustrate this by considering Maxwell’s famous fiction
of the “sorting demons.” Let us imagine a mass of gas contained in a
vessel the walls of which do not conduct heat. Let there be a partition
in this vessel also of non-conducting material, and let there be an
aperture in this partition greater in area than a molecule, but smaller
than the mean free path of a molecule. Now this mass of gas has a
certain temperature which is proportional to the mean velocity of
movement of the molecules. The second law says that heat cannot pass
from a cold region in a system to a hot region without work being done
on the system from outside, nor can an inequality of temperature be
produced in a mass of gas or liquid except under a similar condition.
But “conceive a being,” says Maxwell, “whose faculties are so
sharpened that he can follow every molecule in its course; such a
being, whose attributes are still as essentially finite as our own,
would be able to do what is at present impossible to us.”[20] For the
temperature of the gas depends on the velocities of the molecules, and
in any part of the gas these velocities are very different. Suppose
that the demon saw a molecule approach which was moving at a much
greater velocity than the mean: he would then open the door in the
aperture and let it pass through from - to +. On the other hand, should
a molecule moving at a velocity much less than the mean approach he
would let it pass from + to -. In this way he would sort out molecules
of high from those of low velocity. But the collisions between the
molecules in either division of the vessel would continually produce
diversity of individual velocity, and in this way the difference of
temperature between + and - would continually be increased. Heat would
thus flow from a region of low to a region of high temperature without
an equivalent amount of work being expended.
[20] Impossible, in the sense that while we are unable to “abrogate” a
physical law, Maxwell’s finite demon could, although his faculties were
similar in nature to ours.
Now we must not introduce demonology into science, so, lest this
fiction of Maxwell’s should savour of mysticism, or something
equally repugnant, we shall state the idea involved in it in quite
unexceptionable terms. The conclusions of physics are founded on
the assumption that we cannot control the motions of individual
molecules. In a mass of gas, or liquid, or in a solid, the molecules
are free to move and do move. Their individual velocities and free
paths vary considerably from each other. These motions and paths
are un-co-ordinated--“helter-skelter”--if we like so to term them.
Physics considers only the statistical _mean_ velocities and free
paths. The irreversibility of physical phenomena, the fact that energy
tends to dissipate itself, the second law of thermodynamics, depend
on the assumption that Maxwell’s demons exist only in imagination. We
must appeal to experience now. There is no _a priori_ reason why the
phenomena of physics should be directed one way and not the other, for
it is possible to conceive a condition of our Universe in which, for
instance, solid iron would fuse when exposed to the atmosphere. In such
conditions organisms would grow backwards from old age to birth, with
conscious knowledge of the future but no recollections of the past.
Experience shows, however, that phenomena do tend in one way--_but this
experience is that of experimental physics_, so that for the latter
science Maxwell’s demons do not exist. Now physiology has borrowed from
physics, not only the experimental methods, but also the fundamental
concepts of thermodynamics. The organism, therefore (so physiology
must conclude), cannot control the motions of individual molecules,
and so vital processes are irreversible. But we have seen that the
processes of terrestrial life as a whole are reversible, or tend to
reversibility. We must therefore seek for evidence that the organism
can control the, otherwise, un-co-ordinated motions of the individual
molecules.
The Brownian movement of very small particles of matter is so familiar
to the biologist that we need not describe it. It is doubtless due
to the impact of the molecules of the liquid in which the particles
are suspended. Groups of molecules travelling at velocities above the
mean hit the particle now on one side, and again on the other, and
so produce the peculiar trembling which Brown thought was life. Now
the particle must be below a certain size in order to be so affected.
Are there organisms of this size? Undoubtedly there are, for many
bacilli show Brownian movements, while we have reasons for believing
that ultra-microscopic organisms exist. Also, on the mechanistic
hypothesis there are “biophors,” the size of which is of the same
order as that of the molecules of the more complex organic compounds.
All these must be affected by the molecular impacts of the liquid in
which they are suspended. Can they distinguish between the impacts of
high-velocity molecules and those of mean-velocity ones, and can they
utilise the surplus energy of the former? This has been suggested by
the physicists. In Brownian movement, says Poincaré, “we can almost see
Maxwell’s demons at work.”
The suggestion is not merely a speculative one, for it is well within
the region of experiment. To prove it experimentally we should only
have to show that the temperature of a heat-insulated culture of
prototrophic bacteria falls while the organisms multiply.
Is it not strange that the biologists, to whom the Brownian movement
is so familiar, should have failed to see its possibly enormous
significance? Is it not strange that the biologists, to whom the
distinction between the statistical and individual methods of
investigation is so familiar, should have failed to appreciate this
distinction when it was made by the physicists? Is it not strange that
while we see that most of our human effort is that of _directing_
natural agencies and energies into paths which they would not otherwise
take, we should yet have failed to think of primitive organisms, or
even of the tissue elements in the bodies of the higher organisms, as
possessing also this power of directing physico-chemical processes?
CHAPTER IV
THE VITAL IMPETUS
Two main conclusions emerge from the discussions of the last three
chapters: (1) that physiology encourages no notions as to a “vital
principle” or force, or form of energy peculiar to the organism; and
(2) that although physiological analysis resolves the metabolism of
the plant and animal body into physico-chemical reactions, yet the
direction taken by these is not that taken by corresponding reactions
occurring in inorganic materials. From these two main conclusions we
have, therefore, to construct a conception of the organism which shall
be other than that of a physico-chemical mechanism.
The ordinary person, unacquainted with the results of physiological
analysis, and knowing only the general modes of functioning of the
human organism, has, probably, no doubt at all that it is “animated”
by a principle or agency which has no counterpart in the inorganic
world. This is the “natural” conclusion, and the other one, that life
is only an affair of physics and chemistry, must appear altogether
fanciful to anyone who knows no more than that the heart propels the
blood, that the latter is “purified” in the lungs, that the stomach
and liver secrete substances which digest the food, and so on. It is
difficult for the modern student of biology, saturated with notions of
bio-chemical activities, gels and sols and colloids and reversible
enzymes and kinases and the like, to realise that the belief in a vital
agency is an intuitive one, and that the mechanistic conception of
life is only the result of the extension to biology of _methods_ of
investigation, and not a legitimate conclusion from their _results_.
To the anatomist, the embryologist, and the naturalist, as well as to
the physicist unacquainted with the details of physiology, no less
than to the ordinary person this is perhaps by far the most general
attitude of mind. It would probably be impossible for anyone to study
only organic form and habits and come to any other conclusion than that
there was something immanent in the organism entirely different from
the agencies which, for instance, shape continents, or deltas, or river
valleys. And this conclusion would probably come with still greater
force to the embryologist, even though he still possessed a general
knowledge of physiological science.
The mechanistic conception of life has, without doubt, been the result
of the success of a method of analysis. One sees clearly that just in
proportion as physical and chemical sciences have been most prolific
of discovery, so physiology, leaning upon them and borrowing their
methods, has been most progressive and mechanistic.
Mechanistic hypotheses of the organism may all be traced back to
Descartes, who built upon the work of Galileo and Harvey. The anatomy
of Vesalius and his successors would have led to no such notions,
had not the discoveries of Copernicus, Tycho, and Kepler shown men
an universe actuated by mechanical law. To a thinker like Descartes,
at once the very type of philosopher and man of science, Harvey’s
discovery of the circulation of the blood must have suggested
irresistibly the extension of mechanical law to the functioning of
the human organism, and it is significant that he made this extension
without including a single chemical idea, and yet produced a logical
hypothesis of life as satisfactory and complete in its day as, for
instance, the Weismannian hypothesis of heredity has been in ours.
His hypothesis of the organism was purely mechanical. It has been
said that his organism was an automaton, like the mechanical Diana of
the palace gardens which hid among the rose-bushes when the foot of
a prying stranger pressed upon the springs hidden in the ground. Its
functions were matters of hydraulics: of heat, and fluids, and valves.
His physiology was Galenic, apart from Harvey’s discovery of the motion
of the blood in a circuit, for he did not accept the notion of the
heart as a propulsive apparatus. The food of the intestine was absorbed
as chyle by the blood and carried to the liver, where it became endued
with the “natural spirits,” and then passing to the heart it became
charged with the “vital spirits” by virtue of the flame, or innate
heat, of the heart, and the action of the lungs. This flame of the
heart, fed by the natural spirits, expanded and rarefied the blood, and
the expansion of the fluid produced a motion, which, directed by the
valves of the heart and great vessels, became the circulation. The more
rarefied parts of the blood ascended to the brain, and there, in the
ventricles, became the “animal spirits.”
Subtle and rarefied though they were, these animal spirits were a
fluid, amenable to all the laws of hydro-dynamics. This was contained
in the cerebral ventricles, and its flow was regulated just like the
water in the pipes and fountains of the garden mechanisms. From the
brain it flowed through the nerves, which were delicate tubes in
communication with the ventricles, and which were provided with valves;
and this outward flow corresponds to our modern efferent nervous
impulse. The afferent impulse was represented by the action of the
axial threads contained in the nerve tubuli. When a sensory surface
was stimulated, these threads became pulled, and the pull, acting on
the wall of the cerebral ventricle, caused a valve to open and allowed
animal spirits to flow along the nerve to all the parts of the body
supplied by the latter. In the effector organs, muscles or glands, this
influx of animal spirits produced motion or other effects. This, in
brief, was the physiology of Descartes.
He spoiled it, says Huxley, by his conception of the “rational soul.”
Fearing the fate of Galileo, he introduced the soul into his philosophy
of the organism as a sop to the Cerberus of the Church. It was
unworthy: a sacrifice of the truth which he saw clearly. Is it likely
that Descartes deliberately made part of his philosophy antagonistic to
the rest with the object of averting the censure of the Church? He was
not a man likely to rush upon disaster, but the conviction that what he
wrote had in it something great and lasting must have made it hardly
possible that he should traffic with what he held to be the truth.
The rational soul was something superadded to the bodily mechanism.
It was not a part of the body though it was placed in the pineal
gland; a part of the brain, which by its sequestered situation and
rich blood supply suggested itself as the seat of some important and
mysterious function. Its existence was bound up with the integrity of
the body, and on the death of the latter the soul departed. But the
body did not die because the soul quitted it, it had rather become an
unfit habitation for the soul. Without the latter the functions of
the healthy body might still proceed automatically, and if the soul
influenced action it actuated an existing mechanism, and without that
mechanism it could not act, though the mechanism might act without the
soul. Thought, understanding, feeling, will, imagination, memory, these
were the prerogatives of the soul, and not those of the automatic body.
But the movements of the latter, even voluntary movements, depended on
a proper disposition of organs, and without this they were wanting or
imperfect.
Thus to a thoroughgoing mechanism Descartes joined a spiritualistic
and immortal entity; and this, to the materialism of the middle of
the nineteenth century, was the blemish on his philosophy. Now of
all men who have ever lived he is probably the one who has most
profoundly influenced modern thought and investigation: to us what
he wrote seems strangely modern, and this apparently arbitrary
association of spiritualistic and materialistic elements in life seems
almost the most modern thing in his writings. Being, he said, was
indeed thought, but how could he derive thought from his clockwork
body, with its valves and conduits and wires? No more can we derive
consciousness from the wave of molecular disturbance passing through
afferent nerve and cerebral tracts. We must account for all the energy
of this disturbance, from its origin in the receptor organ to its
transformation into the wave of chemical reaction in the muscle, and we
must regard its transmission as a conservative process. But how does
the state of consciousness accompanying the passage through the cortex
of this molecular disturbance come into existence? None of the energy
of the nerve disturbance has been transformed into consciousness:
the latter is not energy nor anything physical. It is something
concomitant with the physico-chemical events involved in a nervous
process, an “epiphenomenon.” We have to imagine a “parallelism” between
the mechanistic body and the mind. But if we admit that consciousness
may be an effective agency in our behaviour, what is the difference
between modern theories of physico-psychic parallelism and the
Cartesian theory of a rational soul in association with an automatic
body? Descartes denied the existence in animals other than man of the
rational soul; the latter was not necessary. But he, like us, must have
been familiar with reflex actions and must have seen that consciousness
was not invariably associated, even in himself, with bodily activity.
And he must have recognised the great distinction between the
intelligent acting of man and the instinctive behaviour of the lower
animals. There was something in man that was not in the brute.
Thus the first physiology, borrowing its ideas and methods from the
first physics, was, like the latter, a mechanical science. After
Galileo and Torricelli came Borelli with his purely mechanical
conceptions of animal movement, and of the blood circulation,
introducing even then mathematics into biology. There was no chemistry
in these speculations, though Basil Valentine and Paracelsus and
Van Helmont had preceded Descartes and Borelli. This chemistry was
mystical, and though chemical reactions had been studied in the
organism, they were supposed to be controlled by spiritual agencies,
the “archei” of the first bio-chemists. But that notion was to
disappear, and with Sylvius the conception of the animal body as a
chemical mechanism arose. All that was valuable in Van Helmont’s
chemistry was taken up by Sylvius, but in his mind the fermentations of
the older chemists were sufficient in themselves without the mystical
“sensitive soul” and “archei.” With Sylvius and Mayow physiology
became based upon chemical discovery and again became mechanistic, and
remained so until the time of Stahl, when chemical discovery attained
for the time its greatest development.
The seventeenth century ended with the work of Stahl. It is well
known to students of science how the views of this great chemist
sterilised chemical investigation almost until the time of Lavoisier.
The notion of phlogiston as an active constituent of material bodies
entering and leaving them in their reactions with each other was a
clear and simple one, and it served as a working hypothesis for the
chemists who immediately followed Stahl. It was, of course, a false
hypothesis, and retarded discovery to the extent that the greater part
of the eighteenth century is a blank for chemistry, when compared with
the seventeenth and nineteenth centuries. Deprived therefore of the
stimulus afforded by new physico-chemical methods of investigation,
physiology ceased to maintain the progress it had made during the
previous century, and the only great name of this period is that of
von Haller. Comparative anatomy, and zoological exploration, on the
other hand, made enormous advances, and for these branches of biology
the eighteenth century was the great period. It was the period of the
historic vitalistic views--vital principles, and vital and formative
forces. Stahl’s teaching dominated physiology just as it did chemistry.
Chemical and physical reactions occurred in the living body just as
they did in non-living matter, but they were controlled and modified by
the soul, or vital principle. It has been said that Stahl’s vitalistic
teaching retarded the progress of physiology, but it does not seem
clear that this was the case. What did retard physiological discovery
was the lack of progress made by chemistry and physics, and this may
have been the result of the Stahlian phlogistic hypothesis.
However this may be, it seems clear that it was the discoveries of
the great chemists of the close of the eighteenth century that again
introduced mechanistic views into physiology. With the discoveries of
Lavoisier and his successors the latter science acquired new methods
of research and the older working hypotheses were re-introduced.
There has been no recession from this position during the nineteenth
century. Mechanistic biology culminated in the writings of Huxley and
Max Verworn and received a new accession of strength almost in our
own day in the modern discoveries of physical chemistry; and when
physiology became truly a comparative science, and embraced the lower
invertebrates, it became perhaps most mechanistic--witness the writings
of Jacques Loeb.
Of far greater philosophical importance than the physico-chemical
investigation of the functioning of individual organisms has been the
essentially modern experimental study of embryological processes. The
former deals essentially with the _means_ of growth, reproduction, and
so on. We can no longer doubt that the changes which we can observe
taking place in the organism, either the developing embryo or the fully
formed animal, are, in the long run, physico-chemical changes; and in
ultimate analysis we cannot expect to find anything else than processes
of this nature.
But physiological investigation has failed to provide anything more
than this analysis. If we watch the development of the egg of an animal
into a larval form, and continue to trace the metamorphosis of the
larva into the perfect animal, we cannot fail to conclude that, beside
the individual physico-chemical reactions which proceed, there is also
_organisation_. The elementary processes must be _integrated_. There
must be a due order and succession in them. In studying developmental
processes, in considering the developing organism _as a whole_,
we are impressed above all else with the notion that not only do
physico-chemical reactions occur, but that these are _marshalled_
into place, so to speak. When we attempt to make a description of
this integration of those ultimate processes which we can describe
in terms of physical chemistry, physiology fails us. “At present,”
says Morgan, “we cannot see how any known principles of chemistry or
of physics can explain the development of a definite _form_ by the
organism or by a piece of the organism.” It is true that we can attempt
to imagine a physico-chemical mechanism which is the organisation
of the developing embryo; but this must be a logically constructed
mechanism, not only incapable of experimental verification, but which
can also be demonstrated, purely by physical arguments, to be false.
This conclusion may, without exaggeration, be said to be that of modern
experimental embryology.
There have always been (in modern times) two views as to the nature
of the embryological process: (1) that the egg contained the fully
formed organism in a kind of rolled-up condition, and that the process
of development consisted merely in the unfolding (_evolution_)
of this embryonic organism, and in the increase in volume of its
parts. This was the hypothesis of preformation held in the beginning
of embryological science. It involved various consequences: the
limitation, for instance, of the duration of a species, since each
generation of female organisms contained in their ovaries all the
future generations; with other consequences which the preformationists
did not hesitate to accept. (2) The other view was the later one of
epigenesis: the egg was truly homogeneous and the embryo grew from it.
Obviously the acceptance of this hypothesis led to vitalism, and we
find that it was abandoned just as soon as the embryologists recognised
that physics provided a corpuscular theory of matter, when a return
was made to the preformation views of earlier times; views which
lent themselves to the construction of a mechanistic hypothesis of
development.
[Illustration: FIG. 12.]
We may state very briefly the main facts of the development of a
typical animal ovum, such as that of the sea-urchin.
The fertilised ovum divides into two (2), and then each of these
blastomeres divides again in a plane perpendicular to the first
division plane (3). The third division plane is at right angles to
the first two, and it cuts off a tier of smaller blastomeres from the
tops of the first four. There are now (4) two tiers of blastomeres, a
lower tier of large blastomeres and an upper tier of smaller ones. This
is the 8-cell stage. Next, each of these blastomeres divides in two
simultaneously so that the embryo now consists of sixteen cells. After
this the divisions proceed with less regularity, but after about ten
divisions the embryo consists of about 1000 cells (2^{10}), and these
are arranged to form a hollow sphere consisting of a single layer of
cells. The latter are furnished with cilia, and the whole embryo, now
known as the blastula, can swim about by the movements of these cilia.
Further development results in another larval form--the gastrula, and
yet another, the pluteus larva. After this the transformation into the
fully formed sea-urchin occurs.
With various modifications this scheme represents the early development
of a very large number of animals belonging to most groups.
If we study the process of cell-division we shall find it very
complicated. The ovum, immediately after fertilisation, consists of two
main parts, the nucleus and the cytoplasm.
[Illustration: FIG. 13.]
Within the nucleus is a substance distinguishable from the rest; it is
distributed in granules and is called the chromatin (1). When the cell
is about to divide this chromatin becomes arranged in a long coiled
thread (2), and then (3) this chromatic thread breaks into short rods
called chromosomes. Two little granules now appear, one at each end of
the nucleus, and very delicate threads, the asters, appear to pass from
each of these bodies towards the chromosomes (4). Each of the latter
then splits lengthways into two, and a half chromosome appears to be
drawn by the asters towards the poles of the nucleus. The latter then
divides (5) and then the whole cell divides. What thus, in essence,
happens in nuclear divisions is that the chromatin of the nucleus is
more or less accurately halved. Apparently this substance consists of
very minute granules and the whole process is directed towards the
splitting of each of these granules into two. A half-granule then goes
to each of the daughter nuclei. Every time the embryo divides this
process is repeated. Thus each of the (theoretically) 1028 cells of the
blastula contains 1/1028th of the substance of each chromatic granule
in the fertilised ovum.
Pfluger and Roux (in 1883 and 1888 respectively) were the pioneers in
the experimental study of the development of the ovum, and the results
of their work and that of their successors has, more than anything else
in biology, modified and shaped our notions of the activities of the
organism. Roux found, or thought so at least, that the first division
of the frog’s egg marked out the right and left halves of the body, the
one blastomere giving rise to the right half, the other to the left
half. The next division, which separates each of these blastomeres,
marked out the anterior and posterior parts of the embryo. Thus:--
[Illustration: FIG. 14.--The frog’s egg in the 4-blastomere stage seen
from the top.]
Now in an experiment which has become classical Roux succeeded in
killing one of the blastomeres in the 2-cell stage, while the other
remained alive. The uninjured blastomere then continued to develop,
_but it gave rise to a half-embryo only_.
Upon these experiments the Roux-Weismann hypothesis of development--the
“Mosaik-Theorie”--was developed. The lay reader will see how obviously
the facts of nuclear division and the experimental results indicated
above lend themselves to a mechanistic hypothesis. Notice that but
for the physical conception of matter as made up of molecules and
atoms the mosaic-theory would hardly have shaped itself in the minds
of biologists. But this notion of matter consisting of corpuscles must
have suggested that the essential “living material” of the organism
consisted also of corpuscles, as soon as a microscope powerful enough
to see the chromatic granules was turned on a dividing cell prepared
so as to render these bodies visible. Obviously the primordial ovum
contained all the elements of the organisms into which it was going
to develop. But then in the process of division of the ovum all these
chromatic granules are shared out among the cells, and a really very
pretty mechanism comes into existence for this purpose of distribution.
Weismann built up his hypothesis of the germ-plasm upon the
observations we have outlined. The chromatic matter of the nucleus
consists of elements called _determinants_, the determinants themselves
being composed of ultimate bodies called _biophors_. Each determinant
possesses all the mechanism, or factors, necessary for the development
of a part of the body: there are determinants for muscles, nerves,
connective tissues, for the retina of the eye, for hairs of each
colour, for the nails, and so on. All these determinants are contained
in the chromatin of the nucleus of the egg, and in the divisions of the
latter they are gradually separated so that ultimately each cell of
the larva contains the determinants for one individual part, or organ,
or organ-system of the adult body. The right blastomere, for instance,
contains all the determinants for the right side of the frog’s body,
those for the left side being contained in the left half. The process
of cell-division involved in the segmentation of the egg consists
then in the orderly disintegration of this complex of determinants,
and in the marshalling into place of the isolated elements. The cell
body--the cytoplasm--carried out a very subordinate rôle, mainly
that of nourishing the essential chromatic substance. Such was the
Roux-Weismann Mosaic-theory of development in its pristine form.
It is clearly a preformation hypothesis. It is true that the actual
organism is not contained in the germ, but all the parts of the latter,
even the colours of the eyes or hair, are present in it in the form
of the determinants. Obviously it involves a mechanism of almost
incredible complexity. But if we regard it as a working hypothesis of
development this complexity of detail does not matter; its truth would
be indicated by the fact that all analysis of the processes involved
would tend to simplify it and to smooth out the complexity. But this
is exactly what has not happened, for all subsequent investigation has
necessitated subsidiary hypothesis after hypothesis. As a theory of
development it has failed entirely.
If, after one of the blastomeres in the frog’s egg at the 2-cell stage
be killed, the egg is then turned upside down, the results of the
experiment become totally different; the uninjured blastomere develops
into a _whole_ embryo, differing from the normal one chiefly in that it
is smaller. If the uninjured egg in the 2-cell stage be turned upside
down _two whole embryos_, connected together in various ways, develop.
In the frog’s egg the two first blastomeres cannot be separated from
each other without rupturing them, but in the egg of the salamander
they can be separated. After this separation two perfect, but small,
embryos develop. In the egg of the newt a fine thread can be tied
round the furrow formed by the first division. If this ligature be
tied loosely it does not affect development, and then it can be seen
that the median longitudinal plane of the embryo does not correspond,
except by chance, with the first division plane. If the ligature be
tied tightly, then each of the blastomeres gives rise to an entire
embryo. If it is tied in various places monsters of various types are
produced. Therefore there is no segregation of the determinants in the
first two blastomeres. These results, moreover, are not exceptional,
for similar ones have been obtained with other animal embryos, in
fishes, _Amphioxus_, ascidians, medusæ, and hydrozoa, and in some
cases even each of the first four blastomeres develops into an entire
embryo when it is separated from the rest. In the sea-urchin embryo
the blastomeres can be shaken apart; or by removing the calcium which
is contained in sea water the blastomeres can easily be separated from
each other. It was then found by Driesch that each of the blastomeres
in the 16-cell stage could develop into an entire embryo. It is plain,
then, that up to this stage at least there has been no segregation of
the determinants.
Upon the results of these experiments Driesch based his first proof of
vitalism. Let us suppose that there is a mechanism in the developing
egg. Now the embryo which results from the latter sooner or later
acquires a three-dimensional arrangement of parts: head-end differs
from tail-end, dorsal surface differs from ventral surface, and
the parts differ on either side of the median plane. The mechanism
must, therefore, be one which acts in three dimensions, anterior and
posterior, laterally, and dorso-ventrally. We may represent it by a
diagram of three co-ordinate axes, _x_, _y_, _z_; _x_ and _y_ being in
the plane of the paper, and _z_ at right angles to the plane of the
paper. Now in the 2-cell stage the same mechanism must be present,
for this stage develops normally into one entire embryo. But since
_either_ of the blastomeres may develop into an entire embryo, the
mechanism must also be present in each of them, and since in the
16-cell stage each blastomere may develop an entire embryo, it must
be present in each of the sixteen blastomeres. A three-dimensional
mechanism is therefore capable of division down to certain limits.
[Illustration: FIG. 15.]
[Illustration: FIG. 16.]
Suppose now that we allow the sea-urchin egg to develop normally up to
the blastula stage. In this stage it is a hollow sphere, the wall of
which is a single layer of cells. It is similar all round, that is, we
cannot distinguish between top and bottom, right and left, anterior
and posterior regions; but since it develops into a larva in which
all these distinctions become apparent very soon, it must possess the
three-dimensional mechanism, since the activity of the developmental
process is going to produce different structures in each direction. Now
the blastula, by very careful manipulation can be divided, cut into
parts with a sharp knife. Since it is similar all round the direction
of the cut is purely a matter of chance. It can be cut through along
the planes 1 2, 3 4, 5 6, 7 8, for instance; really there are an
infinite number of planes along which the blastula can be cut into
two separate parts, and the direction of the plane is not a matter of
choice, but purely a matter of chance. Nevertheless, each of the parts
into which the larva is cut becomes an entire embryo. For a time the
partial blastula--approximately a hollow hemisphere in form--goes on
developing as if it were going to become a partial embryo, but soon the
opening closes up and development becomes normal. It does not matter
even if the two parts into which it is divided are not alike in size;
provided that a part is not too small, it will follow the ordinary
course of development.
[Illustration: FIG. 17.]
Suppose the blastula opened out on the flat, like the Mercator
projection of a globe on a flat map. Suppose that _a_ is a small element
of it. Suppose that the rectangles _b c d e_, _F G H e_, _I J c L_, _M
N O e_, and as many more as we care to make, represent the pieces of
the blastular wall separated by our operation--they all contain the
element _a_, but this is in a different position in each case. There
are really an infinite number of such parts of the blastula and _a_
occupies an infinitely variable position in each of them.
This demonstration is very important, so let us make it as clear
as possible: Driesch’s logical proof of vitalism may be stated as
follows:--
The different parts of the blastula are going to become different parts
of an embryo.
The part _a_, occupying a definite position in the entire blastula, is
going to become a definite part, having a definite position, in the
embryo;
But each partial blastula becomes an entire embryo and the same part
_a_ occupies a different position in each.
Therefore _any_ part of the blastula may become _any_ part of the
embryo.
Now if a mechanism is involved, it must, according to our ideas of
mechanism, be one which is different in its parts, for each part of it
produces a different result from the others;
But since any part of the mechanism may produce any of the different
results contained in the embryo, every one of its parts must be similar
to every other one.
That is, all the parts of the mechanism are the same, though the
hypothesis requires that they should be different.
We conclude, then, that a mechanism such as we understand a mechanism
to be in the physical sciences cannot be present in the developing ovum.
Nevertheless, an _organisation_, using this term as an ill-defined
one for the present, must exist in the ovum, or the system of
undifferentiated cells into which the ovum divides, during the first
stages of segmentation. In certain animals, Ctenophores (Chun, Driesch,
and Morgan), and Mollusca (Crampton), for instance, separation of the
blastomeres in the first stages of segmentation produces different
results from those mentioned above. In these cases the isolated
blastomeres develop as partial embryos, that is, the latter are
incomplete in certain respects, and this incompleteness corresponds, in
a general way, to the incompleteness of the part of the ovum undergoing
development. We have thus the apparently contradictory results: (1)
each of the first few blastomeres resulting from the first divisions
of the ovum is similar to the entire ovum, and develops like it; and
(2) each of the first few blastomeres is different from the others, and
from the entire ovum, and develops differently from the others, and
from the entire ovum.
Let us try to construct a notion of what this organisation in the
developing ovum must be. In the 16-blastomere stage of the sea-urchin
egg we have a “system” of parts. In the case of normal development each
of these parts has a certain actual fate--it will form a part of the
larva into which the embryo is going to develop: It has, as Driesch
says, a _prospective value_. But let the normal process be interfered
with, and then each of these parts does something else. In the extreme
case of interference, when the blastomeres are separated from each
other, each blastomere, instead of forming only a part of a larva,
forms a whole larva. The _prospective potency_ of the part, that is its
possible fate, is greater than its prospective value. Normally it has
a limited, definite function in development, but if necessary it may
greatly exceed this function.
What any one blastomere in the system will become depends upon its
position with regard to the other blastomeres. When the egg of the frog
is floating freely in water it lies in a certain position with the
lighter part uppermost, and then development is normal, each of the two
first blastomeres giving rise to a particular part of the body of the
larva; that is, each of them is affected by the contact of the other
and develops into whatever part of the normal embryo the other does
not. But let the egg in the 2-cell stage be turned over and held so
that the heavy part is uppermost: the protoplasm then begins to rotate
so as to bring the lighter part uppermost; but the two blastomeres
do not, as a rule, adjust themselves to the same extent, and at the
same rate, and corresponding parts may fail to come into contact with
each other. Lacking, then, the normal stimulus of the other part,
each blastomere begins to develop by itself, and a double embryo is
produced. It is clear, then, both from this case and the last one,
that the actual fate of any one part of the system of blastomeres _is
a function of its position_. What it will become depends precisely on
where it is situated with respect to the other parts.
Driesch, then, calls the system of parts in such cases as the 2-cell
frog embryo, or the 16-cell sea-urchin embryo, an _equipotential
system_, since each part is potentially able to do what any other part
may do, and what the whole system may do. But in normal development
each part has a definite fate and its activity is co-ordinated
with that of all the other parts. It is, therefore, an _harmonious
equipotential system_, each part acting in harmony, and towards a
definite result, with all the others; although if necessary it can take
the place of _any_ or _all_ of the others.
Such an harmonious equipotential system exists only at the beginning
of the development of the egg. It is represented by the 8-cell
stage of Echinus but not by the 16-cell stage, since, though the
1/16-blastomeres produce gastrulæ (the first larval stage), they do
not produce plutei (the second stage). It is represented by the 4-cell
stage of Amphioxus but not by the 8-cell stage. It is not exhibited
even by the 2-cell stage of the Ctenophore egg. What does this mean?
It means that the further development proceeds, the less complete does
the “organisation” inherent in any one part of the system become. “The
ontogeny assumes more and more the character of a mosaic work as it
proceeds” (Wilson).
Or perhaps it means, and this is the better way of putting it, that
the “organisation,” whatever it may be, depends on size. We see this
very clearly in the experiment of cutting in two the blastula of the
sea-urchin. If the pieces are of approximately equal size each will
form an entire Pluteus larva, but if one of them is below a certain
limit of size it will not continue to develop. The “organisation,”
therefore, has a certain volume, and this volume is much greater than
that of any one of the cells of which the fragment exhibiting it is
composed. It is enormously greater than the volume of any group of
determinants which we can imagine to represent the different kinds
of cells composing the body of the Pluteus larva, and still more
enormously greater than the volume of a “molecule” of protoplasm. Now
this association of “organisation” and size is of immense philosophical
importance, for it does away, once and for all, with the idea that
the “organisation” is solely a series of chemical reactions. If
it were, one cell of the blastula would contain it, for on the
mechanistic hypothesis one cell, the egg-cell, contains it, and this
cell can be divided innumerable times and still contain it. The egg
is a _complex equipotential system_ (Driesch), which divides again
and again throughout innumerable generations, and still contains the
“organisation.”
It is in vain that we attempt the misleading analogy of the “mass
action” of physical chemistry, to show that volume may influence
chemical action. In such a mass action what we have is this:--
_A_↓{a} + _B_↓{b} ⇆ _C_↓{c} + _D_↓{d}
the letters _A_, _B_ and _C_ standing for chemical substances present,
and the letters _a_ and _b_, etc., representing the active masses of
these substances. But variations in this active mass affect only the
_velocity_ of the reaction. What we have to account for in our blastula
experiments is the _nature_ of the reaction, and how can velocity or
even nature of reaction affect _form_? If we could show that the form
of the crystals deposited from a solution in some reaction depended on
the volume of the solution, the analogy would be closer, though even
then the difficulties in pressing it would be so enormous as to render
it futile to attempt to entertain it.
A chemical mechanism cannot, then, be imagined, much less described,
and the only other mechanism so far suggested is the Roux-Weismann
one, involving the disintegration of the determinants supposed to be
present in the egg nucleus. Let us suppose (in spite of the incredible
difficulty in so doing) that there is such a mechanism. It must usher
the nuclei containing the determinants of the embryonic structure
into their places: those for the formation of the nerve-centre go
forward; those for the mouth, gut, and anus go backwards and downwards;
those for the arms go forwards, ventrally, and posteriorly, in a very
definite way; and those for the complicated skeleton are distributed
in a variety of directions which defy description. These nuclei are,
in short, moved up and down, right and left, backwards and forwards,
and become built up into a complicated architecture. Suppose we prevent
this. Suppose we compress the segmenting egg between glass plates so
that the nuclei are compelled to distribute themselves in one plane
only: to form a flattened disc in which the only directions are right
and left and anterior and posterior. This has been done by Driesch and
others. On the Roux-Weismann original hypothesis a monstrous larva
ought to result, for the first nuclei separated from each other have
been forced into positions altogether different from those which they
should have occupied had they developed normally. Yet on releasing the
pressure readjustment takes place. New divisions occur so as to restore
the normal form of larva. The Roux-Weismann subsidiary hypothesis is
that the stimulus of the pressure has compelled the nuclei to divide at
first in such a way as to compensate for the disturbance.
Let us remove some of the blastomeres. On the original hypothesis the
determinants for the structures which the nuclei of these blastomeres
contained have been lost. These structures should, therefore, be
missing in the embryo. But nothing of the sort is the result. Other
nuclei divide and replace the lost ones, and the embryo develops as
in the normal mode. The reply is that in addition to the determinants
which were necessary for their own peculiar function, these nuclei
contained a reserve of all others. On disturbance these determinants,
“latent” in all other conditions, became active and restituted the lost
parts.
Let us remove some organ from an adult organism. The most remarkable
experiment of this kind is the removal of the crystalline lens from
the eye of the salamander. Now the lens of the eye develops from the
primitive integument (ectoderm) of the head, but the iris of the eye
develops mainly from a part of the primitive brain. After the operation
a new lens is formed _from the iris_ and not from the cornea. Therefore
the highly specialised iris contains also determinants of other kinds.
Does it contain those for itself and lens only, or others? If it
contains many kinds, then we conclude that even the definite adult
structures contain determinants of many other kinds than their own,
that is, reserve determinants are handed down in all cells capable
of restitutive processes, practically all the cells of the body. Or
does it contain only its own and those of the lens? Then this highly
artificial operation was anticipated, an absurd hypothesis which need
not be considered.
This particular mechanistic process (and no other one is nearly
so plausible) crumbles away before attempts at verification, and
it survives only by the addition of subsidiary hypothesis after
hypothesis. In itself this demonstrates that it is an explanation
incompetent to describe the facts.
What, then, is the “organisation”? It is something elemental, and we
may just as well ask what is gravity, or chemical energy, or electric
energy. It cannot be said to be any of these things or any combination
of them. “At present,” says a skilful and distinguished experimenter,
T. H. Morgan, “we cannot see how any known principle of chemistry or of
physics can explain the development of a definite form by the organism
or a piece of the organism.” “Probably we shall never be able,”
concludes Morgan, who is anything but a vitalist. But does not this
mean just that in biology we observe the working of factors which are
not physico-chemical ones?
We have seen that the physiologist studies something very different
from that which the embryologist or naturalist studies. The former
investigates a _part_ of the animal, arbitrarily detached from the
whole because the complexity of the functions of the simplest organism
is such that all of them cannot be examined at once. He adopts the
methods of physical chemistry in his investigation and whatever
results he obtains are necessarily of the same order. Inevitably,
from the mere nature of his method, he can see, in the organism,
only physico-chemical phenomena. The embryologist, on the other hand,
studies the organism as a whole and seeks to determine how definite
forms are produced, and how a change in the external conditions affects
the assumption of these forms. We have seen with what little success
the attempts to relate embryological processes with physico-chemical
ones alone have met. In all studies of organic form mechanism has
failed. It is useless to attempt to press the analogies of crystalline
form, and the forms assumed in nature by dynamical geological agencies.
If the reader examines these analogies critically he will see that they
are superficial only.
We seem, however, to see in those actions of the organism which are
called “tropistic” or “tactic,” reactions of a purely physico-chemical
nature, and starting with these as a basis a plausible theory of
organic movements on a strictly mechanistic basis might be built
up.[21] A “tropism” is the movement of a fixed organism with respect
to a definitely directed external stimulus. This movement may be that
produced by growth of its parts, or by the differential contraction
or expansion of its parts. A “taxis” we may call the motion of a
freely-moving organism in response to the same directed stimuli. The
movements whereby a green plant turns towards the light are called
heliotropic, and those of its roots in the perpendicular direction are
called geotropic. The motion of the freely-moving larva of a barnacle,
for instance, in swimming towards a source of light are called
“phototactic.”
[21] Many of Jacques Loeb’s remarkable investigations point in this
direction.
In all these cases we have to think of the stimulus as a “field
of energy” in the sense in which physicists speak of electric, or
magnetic, or electromagnetic, or thermal, or gravity fields. In all
these cases the factors affecting the movements of the organism are
directed ones.
An electric field, for instance, (1), is produced by placing
the electrodes of a galvanic cell at opposite extremities of a
water-trough: we imagine the electrons moving from one side of the
trough to the other in parallel lines, and in a certain direction. A
light field (2) would be produced by the radiation of light travelling
in straight lines through the water.
[Illustration: FIG. 18.]
The movements of the organism displaying a tropism or a taxis are not
caused by the stimuli of the field, but are only directed by it. In the
absence of these stimuli it would swim at random. In a field, however,
it will orientate itself in some direction with reference to the lines
of force. A “positively phototactic” animal swims towards the focus
from which the light radiation emanates, and a “negatively phototactic”
one swims in the other direction. On the theory of tropistic and tactic
movements this orientation is produced by the differential stimulation
of the opposite sides of the organism. Let us take as a concrete
example the case of a caterpillar which creeps up the stem of a plant
to feed on the tender shoots near the apex. The animal possesses an
elongated body, with muscles beneath the integument, and sensory
nerve-endings in the latter. Its muscles are in a state of “tone,”
that is, they are normally always slightly tense. The incident rays of
light affect the dermal sense-organs, stimulating ganglionic centres
and setting up efferent impulses which descend to the muscles. Let us
suppose the animal is moving so that the longitudinal axis of its body
is at an angle, say of 45°, to the direction of the incident light:
one side of the body is therefore stimulated and the other is not.
The stimulation of the lighted side sets up efferent nerve impulses
which descend to the muscles of this side and increase their tone
(or else the lack of stimulation of the other side produces impulses
which inhibit the muscular tone, or impulses which would otherwise
preserve the tone cease in the absence of light stimulation). In any
case the muscles of the lighted side contract, and the body of the
caterpillar moves so that it sets itself parallel to the direction of
the radiation. Both sides of the body are then equally stimulated and
the animal moves towards the light.
The animal feeds and it then creeps back down the plant. Why does it do
this? Because, says Loeb, the act of feeding has reserved the “sign” of
the taxis. Before, when it was hungry, it was positively phototactic,
but the act of feeding (all at once, it would appear, before digestion
and assimilation of the food itself) has produced chemical substances
in the muscles which cause the latter to relax in response to an
impulse which previously produced contraction.
The nervous link is not, of course, a necessary one. The stimulation
by the energy of the field may affect the muscle substance directly,
or it may, as in the case of a protozoan animal, affect the general
body protoplasm in the same way. In the majority of cases, however,
the orientation would be affected through the chain of sense-organ,
afferent nerve, nerve centre, efferent nerve, and effector organ. This
is the chain of events which on this hypothesis causes a moth to fly
into a flame, or a sea-bird to dash itself against the lantern of a
lighthouse.
A taxis is, then, an inevitable response by movement in a definite
direction, to a directed stimulus. Including also tropisms it may be
admitted that the movement is a purposeful, or at least, a useful one
in some cases, as for instance the heliotropism and geotropism of the
green plant. If we admit that Loeb’s description of the feeding of the
caterpillar, as a tactic act, is true, we may also call this a useful
act. But in the majority of cases tropisms and tactes are acts which
appear to be of no use to the organism. The invasion of a part of the
body which is irritated by a poison (as in inflammation) by leucocytes,
is useful to the body itself, but we must regard the leucocytes as
organisms, and their tactic motion leads to their destruction, and so
also with other analogous acts. Just because of this we find difficulty
in accounting for their origin in terms of natural selection.
This does not matter so much, since it can hardly be maintained now
that the tropistic or tactic act has any reality except in a very
few cases--the motions of plants, galvano-taxis, the chemico-taxic
movements of bacteria and leucocytes, and some other analogous cases,
perhaps, are these exceptions. It can hardly be doubted that the
extension of the concept to cover the motions of many invertebrates,
and even some vertebrate actions, by Loeb and his school is a straining
after generality which has not been justified. The hypothesis, as Loeb
has stated it, is evidently almost certainly a logical one and was
obviously elaborated as a protest against the anthropomorphism which
saw in the flying of a moth into a flame the expression of an emotion;
or in the movements of a caterpillar on a green shrub the expression
of hunger and satiety and of the inherited experience of the animal;
or in the avoidance by a _Paramœcium_ of a drop of acid the emotion
of dislike of the feeling of pain. Well, let it be granted that this
is so, and that the protest was a useful one, for it is obviously
impossible that these notions as to the causes of the movements can
be verified: does it improve matters to take refuge in an hypothesis
which is just as purely physico-chemical dogmatism as the other is
anthropomorphism? But the former hypothesis is at all events one which
is susceptible of experimental verification and in this lies its
usefulness, inasmuch as it has stimulated investigation. It is evident,
however, that this verification has not yet been made. The differential
afferent impulses set up by the energy-field; the increases or
inhibition of muscular tone; the presence of photo-sensitive substances
in the tissues of tactically acting lower animals; the change of
velocity of chemical reaction, in these cases, which ought to follow
stimulation--all these things _could_ be verified if they possess
reality. Yet it is only indirect proofs, capable perhaps of other
interpretations, and not direct experimental ones, which have so far
been adduced in favour of a general theory of tropisms.
Moreover, the close analysis of the actions of some of the lower
organisms by Jennings has shown that the tactic hypothesis is probably
false in the majority of cases. This observer studied the acting of
the organisms themselves and not the beginning and end of the series,
and he shows that the behaviour of the organisms is far more obviously
described by saying that it adopts a method of “trial and error.” Let
us suppose a number of infusoria (_Paramœcium_) in a film of water, at
one part of which is a drop of acetic acid slowly diffusing out into
the surrounding medium. There is a zone of changing concentrations
round the drop: if we draw imaginary contours through the points where
the concentration is approximately the same (the concentric rings in
the diagram), and then draw straight lines normal to these rings (the
radial lines) we can construct a “field” analogous to an electric or
magnetic field. The animal on approaching the field ought to orientate
itself and take the direction of the “lines of force.” It does not,
however, behave in this way, but only enters the field at random.
Having entered, it remains within a part where the concentration is
within certain limits. If it approaches the margin of this limited
field it stops, swims backwards, revolves round its own axis, and then
turns to the aboral side; and it repeats this series of movements
whenever it approaches (by random) a region where the concentration is
too high, or one where it is too low. In this, and other organisms we
see then what Jennings has called a typical “avoiding reaction,” the
precise nature of which depends on the “motor-system” of the animal.
Its general movements are random ones, but having found a region
of “optimum conditions” (conditions which are most suitable in its
particular physiological state), it remains there.
[Illustration: FIG. 19.]
Suppose (what indeed repeatedly happens) that an extensive “bed” of
young mussels forms on a part of the sea bottom. In a short time the
bed becomes populated by a shoal of small plaice feeding greedily
on the little shellfish. In their peregrinations the fishes must
repeatedly pass out beyond the borders of this feeding-ground. Usually,
however, they will return, for failing to find the food they like they
swim about in variable directions and so re-enter the shellfish bed.
Suppose (this was really a fine experiment made by Yerkes) a crab is
confined in a box from which two paths lead out but only one of which
leads to the water. The animal runs about at random, finds the wrong
path, retraces it, tries again and again, and then finds the right
path and gets back to the water. If the experiment is repeated the
animal finds the right path again with rather less trouble, and after
many trials it ends by finding it at once on every repetition of the
experiment.
All this discussion of concrete cases leads up to our consideration
of the modes of acting in the higher organisms. On the strictly
mechanistic manner of thinking the actions of the organism in general
are based on reactions of the tactic kind--inevitable reactions the
nature of which is determined, and which follow a stimulus with a
certainty often fatal to the organism displaying them. Accepting these
tactic reactions as, in general, truly descriptive of the behaviour
of the organism, we can build up a theory of instincts. In their
simplest form instincts are reflexes--tactic movements. In their more
complex forms they are concatenated reflexes, or tactes. A complicated
instinctive action is one consisting of many individual actions, each
of which is the stimulus for the next one; or, of course, it may
also be complex in the sense that several simple reactions proceed
simultaneously, upon simultaneous stimulation of different receptors.
Now the extension of all this to movements of a “higher” grade is
obvious.
Let us note in the first place, that the stimuli so far considered
in all the examples quoted are simple elemental ones. There are, of
course, relatively few such stimuli: gravity, conducted heat (the
kinetic energy of material bodies), radiated heat (the energy of the
ether), electric energy, chemical energy, and mechanical contact or
pressure (including atmospheric vibrations). In all these cases we
have a definite, measurable, physical quantity, with which we must
relate a definite response in the form of a definite measurable,
physico-chemical reaction. There should be a functionality between the
stimulus and response, a definite, quantitative energy-transformation.
To take a concrete example, a certain quantity of light energy falling
upon the receptor organs of Loeb’s caterpillar ought to transform
into another quantity of “nervous energy,” and this travelling in
an analogous way to a “wave of explosion” ought to transform into
an energy quantity of some kind, which initiates another “wave of
explosion” in the muscle substance. All these transformations must
be quantitative ones, and the energy of the individual light must
be traced from the receptor organ to the points in the muscle where
it disturbs a condition of false equilibrium in the substance of
the latter. Nothing less than this is required to demonstrate the
purely physical nature of a reaction, on the part of the organism,
to an external stimulus. It may safely be said that physiological
investigation has not yielded anything even approximating to such an
experimental demonstration.
What are the stimuli to the actions of a higher organism? It is true
that their elements are energies such as we have indicated, but these
energies are integrated to form _individualised stimuli_ (Driesch).
The stimulus in an experimentally studied taxis is, perhaps, a field
of parallel pencils of light rays of definite wave length; but in the
action of a man, or a dog say, the stimulus is an immensely complicated
disturbance of the ether, producing an _image_ upon the retina of
the animal. A sound stimulus employed in an investigation may be the
relatively simple atmospheric disturbance produced by the sustained
note of a syren or violin-string; but the stimulus in listening to an
orchestra may consist of dozens of notes, with all their harmonies,
sounding simultaneously at the rate perhaps of some hundred or two in
the minute. All these are _integrated_ by the trained listener, and one
or two false ones among the multitude may entirely spoil the effect
of the execution. Surely there is here something more than a mere
difference in degree.
More important still is the strict functionality between stimulus
and action that the theory of tactic responses imposes on itself.
Putting this very precisely (but no more precisely than the theory
demands), we say that [Sigma]_A_ = _f_(_x_, _y_, _z_), that is, the
series of actions [Sigma]_A_ (the dependent variable) is a mathematical
function of the independent variables _x_, _y_, _z_. Now is there
anything like this functionality between the acting of the higher
animal and the stimulus? Evidently there is not. We recognise someone
whom we know very well by any one of a hundred different characters,
mannerisms of walk, speech, dress, etc. He or she is the same person,
whether seen close at hand, or afar off, or sideways, or in any one
of almost infinitely different attitudes, and we respond to each
of these very different physical stimuli by the same reaction of
recognition: pleasure, dislike, avoidance, greeting, or whatever it
may be. To a sportsman shooting wild game the stimulus may be some
almost imperceptible tint or shading in cover of some kind, differing
so little from its environment as hardly at all to be seen, yet, to
his experience, upon this almost infinitesimal variation of stimulus
depends his action with all its consequences. In Driesch’s example
two polyglot friends met and one says to the other, “My brother is
seriously ill,” or “Mon frère est séverèment malade,” or “mein Bruder
ist ernstlich erkrankt.” Here the physical stimulus is fundamentally
different in each case, but the reaction--the expressions of sympathy
and concern, the discussions of mutual arrangements, etc., are
absolutely the same. Or let the one friend say to the other, “My
mother is seriously ill,” and in spite of the very insignificant
difference between the consonantal sound _br_ in this sentence and the
corresponding sound _m_ in the other English sentence, the reaction,
that is, the subsequent conversation, and the arrangements between the
two friends may be entirely different.
Putting this argument in abstract form we may say, generally, that
two stimuli, which are, in the physical sense, entirely different
from each other, may produce absolutely the same series of reactions;
and conversely two stimuli differing from each other in quite an
insignificant degree may produce entirely different reactions. It is
also easy to see, by analysis of the antecedents to the actions of the
intelligent animal, that these stimuli are, in the majority of cases,
not elemental physical agencies, but individualised and integrated
groupings of these agencies; and that the animal reacts, not to their
mathematical sum, as it should do on a purely mechanistic hypothesis
of action, but to the typical wholes which are expressed in these
groupings.[22]
[22] Thus to the ordinary woman the sight of a cow in the middle of a
country road produces a certain definite feeling of apprehension, which
is always the same although the optical image of the animal differs
remarkably in different adventures.
It is no answer to this argument to say that it is not the actual
atmospheric vibrations (in the case of the conversation), nor the
optical image (in the case of the recognition of a friend), which
are the true stimuli, but rather the mental conditions, or states of
consciousness, aroused by these physical agencies. If we are to adopt
a strictly mechanistic method of explaining actions, such a method as
that indicated by Loeb’s hypothesis of the purely tactic behaviour
of his caterpillars, then these atmospheric vibrations and optical
images are most undoubtedly the true stimuli, and the reactions
must be functions of them in the mathematical sense. But since
this strict functionality does not exist in any behaviour-reaction
closely analysed, we must grant at once that it is, indeed, _not_ the
physical series of events that determines the actual response, but
truly the conscious state immediately succeeding to these physical
sense-impressions. Now let us see to what conclusions this admission
leads us.
Between the external stimulus (the atmospheric undulations impinging
on the auditory membranes, or the light radiations impinging on the
retinæ) and the behaviour-reaction something intervenes. This is the
individual history of the organism, the “associative memory” of Jacques
Loeb, the “physiological state” of Jennings, the “historical basis of
reacting” (historische Reaktionsbasis) of Driesch, or the “duration”
of Bergson. The last concept is the most subtle and adequate one
and we shall adopt it. The physical stimulus, then, leads to a state
of consciousness, a perception, and this is succeeded by the action.
What is the perception? There may be no perception in a reflex action;
there is none in a taxis.[23] These kinds of reaction follow inevitably
from the nature of the stimulus--depend upon the latter, in fact;
but we cannot fail to observe that the intelligent behaviour of the
higher animal involves choice between alternative kinds of action. The
perception, then, is this choice, or it is intimately associated with
it. But it is something more than the choice of one among many kinds
of response. The whole past experience of the animal enters into the
perception, or at least all that part of the past experience which
illuminates, in any way, the present situation. What the intelligent
animal does in response to a stimulus depends not only on the stimulus
but on all the stimuli that it has received in its past, and on all
the effects of all those stimuli. Into the perception that intervenes
between the external stimulus, then, and the action by which the animal
responds what we usually call its memory enters. Its _duration_ is
really the something which is changed by the stimulus, and which then
leads to the behaviour-reaction.
[23] We do not find this explicitly stated in this way in mechanistic
biological writings. None the less it is implied, and is the legitimate
conclusion from the arguments used.
Duration, then, is memory, but it is more than memory as we usually
think of this quality. The past endures in us in the form of “motor
habits,” and when we recall it we may act over again those motor
events. Careful introspection will readily convince the reader that in
recalling a conversation he is really _speaking inaudibly_, setting in
motion the nerves and muscles of his vocal mechanisms. Actions that
have been learned endure; in some way cerebral and spinal tracts and
connections become established and persist: undoubtedly when a cerebral
lesion destroys or impairs memory it is these physical nerve tracts and
cells that become affected. But in addition to this we have pure memory
(Bergson’s “souvenir pur”). What, for instance, is the visual image
of some thing seen in the past, which most people can form, but pure
recollection?[24]
[24] A visual image may, of course, be something that has never been
actually seen. But then its elements have had actual perceptual
existence in the past.
All the past experience of the organism--all its perceptions, and
all the actions it has performed--endures, either as motor habits or
mechanisms, or as pure memories. All this need not be present in its
consciousness; the motor habits would not, of course, and only so
much of the past would be recalled as would be relevant to the choice
which the organism was about to make of the many kinds of responses
possible to its motor organisations. Out of this past it would select
all that was connected in any way with the actions which were possible
to it in the present. It would recall all actions previously performed
which resembled the one provisionally decided upon; but recalling also
the other circumstances associated with those past actions, it would
discover something which would lead it to modify that provisional
action. Now in describing the whole behaviour of the acting organism
in this way are we doing any more than simply expressing in more
precise terms the “commonsense” notions of the ordinary person? The
latter would sum up all this discussion by saying that what he would
do in any set of circumstance depended not only on the circumstances
themselves but upon his experience. Physiology shows us as clearly as
possible that in the stimulation of a receptor organ, the propagation
of a nervous impulse along an afferent nerve, the transmission of this
impulse through the cord or brain, or both--in the propagation again of
the impulse through an efferent nerve and the transformation of this
impulse into a releasing agency, setting free the energy potential in
the muscle substance--that in all this there can be nothing more than
physico-chemical energy-transformations. All this is clear and certain.
But why should the same afferent stimuli, entering the central nervous
system at different times by the same avenues, and in the same manner,
traverse different tracts, and issue along different efferent nerves,
producing different results? Or why should different stimuli entering
the central nervous system take the same intra-cerebral paths and then
affect the same efferent nerves and effector organs? It is because
these stimuli lead to perceptions which fuse with, and become part of
the duration of, the organism. And the response then becomes a response
not to the physical stimulus, but to the duration modified in this way.
Can we conceive of any physical mechanism in which the duration of the
organism accumulates? Can we think of any way in which memories are
stored in the central nervous system? When we say “stored,” it is our
ingrained habit of thinking in terms of space and number that makes
us regard memories as laid by somewhere, in the way we file papers
in a cabinet, or store specimens in a museum. Supposing perceptions
are stored in this way, we think of them as stored or recorded in the
same way as a conversation is recorded and stored in a phonograph. The
phonograph can reproduce the conversation just as it was received,
but what we make use of when we utilise our experience is obviously
the elements of that experience, selected and re-integrated as we
require them. There must, then, be something like an analysis of our
perceptions, a dissociation of these into simple constituents, and a
means of restoring and recording these constituents in such a way that
they can be recombined in any order, and again made to enter into our
consciousness.
It is quite possible to imagine such a mechanism. Let us suppose
that an efferent impulse enters the cerebral cortex _via_ any one
axon: there is a perfect labyrinth of paths along which the impulse
may travel. Everywhere in the central nervous system we come upon
interruptions of nervous paths formed by inter-digitating arborescent
formations. The twigs of these arborescences do not, apparently, come
into actual contact with each other and the impulse leaps across the
gap between them. This gap is, of course, exceedingly narrow, and one
can almost speak of it as a membrane, since it must be occupied by some
organised substance. It has been called the synaptic membrane. Let us
suppose that a stimulus of a certain nature passes through the synapse,
modifying it physico-chemically as it passes. Thereafter a stimulus
of similar nature will tend to pass across this particular synapse,
the resistance of the latter having been decreased. It will thus tend
to travel by a definite tract through the central nervous system.
Now the latter we may regard in a kind of way as a very complicated
switchboard, the function of which is to place any one stimulus (or
series of stimuli) out of many in connection with any one motor[25]
mechanism (or series of mechanisms) out of many. A motor habit, or
path, is then established and will persist.
[25] Or more generally _effector_ mechanism. This enables us to include
reactions, such as secretory ones, which are not motor.
Such a conception is clear and reasonable in principle, and all work on
nervous physiology tends to show that it is a good working hypothesis.
We cannot read modern books without feeling that immense advances will
be made by its aid. But the complexity of the brain of the higher
vertebrate is so incredibly great, and the difficulties of imagining
the nature of the necessary physico-chemical reactions in the synapses,
and elsewhere, are so immense that experimental verification may be
impossible. And all that we have said applies to a single elemental
stimulus, yet in any common action the stimulus is a synthesis of
almost innumerable simple ones, while the response is also a synthesis.
The optical image of almost any object contains a very great number of
tints and colours differing almost imperceptibly: there must at least
be as many simple stimuli as there are rod or cone elements in the part
of the retina covered by the image. The motor responses consist of a
multitude of delicately adjusted and co-ordinated muscular contractions
and relaxations. If we are to accept a mechanistic hypothesis of
action, of this kind, and which includes only such processes as
are suggested above, it is not enough that a logical description,
consistent in itself, and consistent with physico-chemical knowledge,
should be formulated. The mere statement of such an hypothesis does not
carry us far. If it is, in essence, mechanistic, it must be capable of
experimental verification in detail.
Even if it were verified experimentally it would still leave untouched
the problem of consciousness. All that we have considered are series of
physico-chemical energy-transformations. How, then, does consciousness
arise? We cannot even imagine its association in a functional sense
with the train of events forming an afferent impulse. In some form or
other mechanism must assume a dualism--a parallelism of physical and
psychical processes. Physical events in the central nervous system
are associated with psychical ones--when the former occur so do the
latter--yet the former are not “causes” in any physical sense of
the latter. Consciousness follows cerebral energy-transformations
as a parallel “epiphenomenon.” At once we leave the province of
mechanism, and how can we remain content with such a limitation of
our descriptions? And if we conclude, as we seem obliged to do, that
consciousness is an affective agency in modifying our responses to
external stimuli, does not this in itself show that our concept of
behaviour as a purely physico-chemical process is insufficient in its
exclusiveness?
We return to a consideration of the main results of experimental
embryology in a later chapter, but let us notice here what is the
direction in which these results, and those of the analysis of
instinctive and intelligent action, carry us. It is towards the
conclusion that physico-chemical processes in the organism are only
the _means_ whereby the latter develops, and grows, and functions,
and acts. In the analysis of these processes we see nothing but the
reactions studied in physical chemistry; but whenever we consider
the organism as a whole we seem to see a co-ordination, or a control
or a direction of these physico-chemical processes. Nägeli has said
that in the development of the embryo every cell acts as it if _knew_
what every other cell were doing. There is a kind of autonomy in the
developing embryo, or regenerating organism, such that the normal,
typical form and structure comes into existence even when unforeseen
interference with the usual course of development has been attempted:
in this case the physico-chemical reactions which proceed in the normal
train of events proceed in some other way, and the new direction is
imposed on the developing embryo by the organisation which we have to
regard as inherent in it. This same direction and autonomy must be
recognised in the behaviour of the adult organism as a whole. What
is it? We attempt to think of it as an impetus which is conferred
upon the physico-chemical reactions which are the manifestations of
the life of the organism. It is the _élan vital_ of Bergson, or the
_entelechy_ of Driesch. What is included in these concepts we consider
in the last chapter of this book; and before so doing it will be
necessary to consider the organism from another point of view, that
of its mutability when it is regarded as one member of a series of
generations.
CHAPTER V
THE INDIVIDUAL AND THE SPECIES
What is an individual organism? A Protozoan, such as an _Amœba_ or a
_Paramœcium_, is a single cell: it is an aggregate of physical and
chemical parts, nucleus, cytoplasm, etc., and no one of these parts
can be removed if the organism is to continue to live. The cell can
be mutilated to some extent, but, in general, its life depends on the
integrity of its essential structures, and it cannot be divided without
ceasing to be what it was. It contains the minimum number of parts
which are necessary for continued organic existence.
Such an organism as a _Hydra_ consists of an aggregate of cells which
are not all of the same kind. The outer layer, or ectoderm, is sensory
and protective, and contains organs of aggression; while the inner
layer consists of cells which subserve the functions of digestion and
assimilation. All these parts are, in general, necessary for the life
of the _Hydra_. They can be mutilated; the animal can be cut into
two parts, and each of these parts may regenerate, by growth, the
part that was removed. Yet the existence of ectoderm and endoderm, in
a certain minimum of mass, is necessary for this regeneration. The
higher animal, or Metazoon, is therefore an aggregate of cells, each of
which is equivalent to the individual Protozoon; but these cells are
not all alike--that is, there is differentiation of tissues in the
multicellular organism.
Again, the Cœlenterates provide examples of animals which are
aggregates of parts, each of which is the morphological equivalent
of a single _Hydra_. Such an animal as a Siphonophore, for instance,
consists of zooids, and each of these units has the essential structure
of a _Hydra_. But the zooids are not all alike: some of them subserve
the function of locomotion, others of aggression, others of digestion
and assimilation, and so on. Here, again, the whole organism may be
mutilated; parts may be removed and regeneration may occur; but, as
a Siphonophore, all of the different zooids must be present if the
characteristic functioning of the animal is to continue.
The Protozoon is, therefore, an individual of the first order, the
_Hydra_ an individual of the second order, and the Siphonophore an
individual of the third order. Some such conception of degrees of
individuality will probably be regarded as satisfactory by most
zoologists, yet consideration will show that it is very inadequate.
Many unicellular plants and animals may consist of a number of cells,
which are all alike. The Diatoms and Peridinians reproduce by the
division of their cell bodies and nuclei, and the parts thus formed
may remain in connection with each other. A Diatom may consist of one
cell, or it may consist of a variable number of such connected together
by filaments, or in other ways; and the dissociation of such a series
may occur without interfering in any way with the functioning of the
parts separated. A Tapeworm consists of a “head” or scolex, containing
a central nervous mass and organs of fixation; and organically
continuous with this is a series of segments or proglottides. These
proglottides are formed continuously from the posterior part of the
scolex, and they may remain in connection with each other, and with the
central nervous system and some other organs which are concentrated
in the scolex. Nevertheless, each proglottis contains a complete
set of reproductive organs; it has locomotory organs so that it can
move about, and can fix itself to any surface into which it comes in
contact. It can lead, for a considerable time, at least, an independent
existence apart from that of the scolex and the other proglottides with
which it was originally in continuity. In the majority of Polyzoa, the
common Sea-Mat, for instance, the organism consists of a very large
number of polypes or zooids, each of which secretes an investment of
some kind round itself, but all of which may be connected together
by a common flesh. In many Zoophytes there is essentially the same
structure. In Corals there are very numerous zooids, each of which
lives in a calcareous calyx secreted by itself. Polyzoa, Zoophytes,
and Corals are individuals of the third order, and we might regard
the tapeworm strobila--the scolex with its chain of proglottides--as
belonging also to the same category. Nevertheless, a part of a Polyzoan
or Hydrozoan colony, or a proglottis from a tapeworm, may become
detached, when it will continue to live and reproduce and exhibit all
the characteristic functioning of the species to which it belonged.
Such an animal as a _Hydra_, or a Planarian or Chætopod worm, or a
starfish, may be cut into several pieces, and provided that each of
these pieces exceeds a certain minimum of mass, it will regenerate
the whole structure of the organism of which it formed a part. In the
developing embryo of the Sea-urchin the eight-cell stage may be treated
so that the blastomeres may come apart from each other: each of them
will then begin to segment again and will reproduce the typical larval
Sea-urchin. The parasitic flat-worm, known as the liver-fluke, produces
larvæ which develop to form other larvæ called rediæ. Each redia
normally develops into another larval form, called a cercaria, which
finally develops into the adult worm. But in certain circumstances
each redia may divide and reproduce a number of daughter-rediæ, and
there may even be several generations of these larvæ. In many lower
animals buds may be formed from almost any part of the body, and each
of these buds may reproduce the entire organism. In plants the entire
organism may be grown from a very restricted part or cutting. Thus
the individual, whether of the first, second, or third order, may be
divided without necessarily ceasing to be what it was.
Regeneration of fragments detached from the fully developed adult
body so as to form complete organisms does not, in general, occur
among the higher animals, nor, as a general rule, does reproduction by
bud-formation occur. When such animals reproduce, an ovum develops to
form a large mass of cells, which later on become differentiated to
form the tissues and organs of the adult body. But a relatively small
number of the undifferentiated cells persists in the ovaries of the
females, or in the testes of the males, and each of these cells may
again develop and reproduce the organism. There is apparently no limit
to this process: any animal ovum may become divided successively so
that an infinite geometrical series is produced, and in every term of
this series all the potentialities of the first one are contained.
The physical concept of individuality--that which cannot be divided,
or which may not be divided without ceasing to be what it was--such
individuality as the chemical molecule possesses cannot be applied
to the organism. Any definition that involves the idea of materiality
fails. Obviously the notion of the individual most commonly met with
in zoological writings--that it is the product of the development of
a single ovum--fails, for, logically applied, it would regard the
entire progeny of the ovum, that is, all the organisms belonging to the
species, as the individual. It is clear that the difficulties of the
concept arise from our attempt to identify the life of the organism
with the material constellation in which this life is manifested. In
the course of generation after generation the ovum becomes divided
and grows and is again divided, and so on without apparent limit. But
if we assume that the “organisation” or “entelechy” is material and
is capable of this infinite divisibility without impairment of its
attributes, do we not extend to matter a property which belongs only to
the concepts dealt with by mathematics?
The discussion of individuality with regard to the organism, considered
as a morphological entity, is, indeed, rather a formal one, and it is
valuable only in so far as it has for its object the establishment of
the most convenient terminology. Nevertheless, the notion of organic
individuality is clear to us though it is a notion felt intuitively and
incapable of analysis. We see in nature animals like ourselves, and
we do not doubt that each of them is an entity isolated from the rest
of the universe, and to which the rest of the universe is relative.
We ourselves are primarily centres of action. Motion, or change of
position with respect to some object apart from ourselves in nature, is
only relative, and there is no standard or point in the universe which
is motionless and to which we can refer the motion of a body apart
from our own. But the motion of our own body is something felt or
experienced intuitively, something absolute. As we move, the universe,
our universe rather--that is, all that we _act upon, actually or in
our contemplation_--contracts in one direction and expands in another.
We feel ourselves to be apart from it although we may, to some extent,
control it. We have no doubt that the higher animals have this feeling
of isolation from, and relation to, an universe which is something
apart from themselves; though, of course, the attempt to demonstrate
this leads to all the kinds of difficulties suggested in our attempt to
discuss individuality. It is a conviction so strongly felt that we have
no doubt about it. The organic individual we may then describe as an
isolated, autonomic constellation of physico-chemical parts capable of
indefinite growth or reproduction.[26]
[26] The description is, of course, only a convenient one. The notion
of individuality, as it is expressed in the earlier part of this
paragraph, is an intuitively felt, or subjective, one. It is best
called personality.
What is reproduction? It is organic growth by dissociation accompanied
in the higher organisms by differentiation and reintegration. To
make this statement clear, we must now consider the phenomena of
reproduction in the lower and higher organisms.
We know purely physical growth. If a small crystal of some suitable
substance be suspended in an indefinitely large quantity of a solution
of the same chemical substance it will begin to grow, and there is no
apparent limit to the mass which it may attain. Such giant crystals
may be grown in the laboratory or they may be found in rock masses.
Growth here is a process of accretion in which a particular form is
maintained. Form in inorganic nature may be essential or accidental.
Accidental forms are such as are partially the result of a very great
number of small and un-co-ordinated causes: the form of an island or a
mountain suffering erosion, or the shape of a river valley or delta,
or the arrangement of the stones forming a moraine at the side of a
glacier. Essential forms are such as are assumed as the result of the
operation of one or a few co-ordinated causes, and such are the forms
of crystals. They are invariable, or they vary within very small limits
about an invariable mean form.
The form of a crystal depends on the structure of the molecules of the
chemical substance from which it is produced. We cannot, of course,
speak of the shape of a molecule, but we know that the atoms of which
it is composed have certain positions in space relative to each
other--positions which are conceptualised in the structural formulæ of
the chemists. In the solution, or mother-liquor, these molecules move
freely among each other, but in the crystal they become locked together
and their motions are restricted. The shape of the crystal depends on
the way in which the molecules are locked together, or on the way in
which they are arranged. A cube may be built up by the arrangement of a
number of very small cubes: obviously we could not make a cube from a
number of very small hexagonal prisms if the latter were to be packed
together in such a way as to occupy the minimum of space. An infinitely
great number of cubes might also be formed by adding single layers of
very small cubes to the faces of an already existing one--that is,
by the accretion of elements of essentially similar form. In every
cube (or crystal) of this infinite number the geometrical form would
be the same, and if we were to measure any one side of any cube of
this series we should find that the total surface would always be a
definite function of the length of this side. The mass of a cube would
also be a function of such a measurement: it would be _al_^3, _a_ being
a constant depending on the unit of mass and on the specific weight of
the substance of which the crystal was composed. If we take a series of
crystals of increasing size, this relation holds for every one of them:
_M_ = _al_^3, _M_ being the mass, _a_ the constant referred to above,
and _l_, the independent variable, being any one length of a side of
the crystal.
If the organism grows by accretion in the same way as does a crystal,
this relation ought also to hold in all the exclusiveness with which
we expect it to hold in the growth of a crystal. But it does not so
grow. Its growth is something essentially different, and none of
the superficial analogies so prevalent nowadays ought to obscure
this difference. The organism may grow by accretion, thus layers of
calcareous matter may be added to the outside of a membrane bone
from the investing periosteum, or it may grow by the deposition
of matter within the actual cell bodies, (the process of growth
by intussusception of the plant physiologists). But the extent of
growth by accretion is strictly limited in all organisms: for each
there is a maximal mass determined by the nature of the animal or
plant, and this mass is that of the unicellular organism itself, or
that of the cells of which the multi-cellular organism is composed.
There may also be growth by accretion in the case of the formation of
skeletal structures, which are laid down by the agency of the cells
of the organism but if we confine our attention to the growth of the
actual living substance we shall see that accretion ceases when the
mass characteristic of the cells has been attained, when growth by
dissociation begins. The cell then divides, and each of the parts
into which it has divided grows to the limiting size, and division
again occurs. This is what happens in the case of the growth of the
Sea-urchin egg to form the larva, or blastula. The ovum segments
into two blastomeres, each of which then grows to a certain extent,
and again segments into two blastomeres. After the completion of ten
divisions there are about 1000 cells which are arranged so as to form a
hollow ball--the blastula.
[Illustration: FIG. 20.--The Sea-urchin Gastrula larva in section.]
Differentiation is now set up. In the blastula stage all the cells
are alike, actually and potentially. But soon one part of the hollow
ball of cells becomes pushed inwards, and the cells of this inturned
layer become different from those of the external layer, while
cells of a third kind appear in the space between the external and
internal layers. This is the process of differentiation leading to the
development of the various tissues--protective, sensory, digestive,
skeletal, etc. The cells still continue to divide and grow to their
maximal size, but when the process of differentiation begins, the
cells which are formed are not quite the same as those from which they
originated. Finally, however, when the rudiments of all the tissues
of the adult body have been laid down, the cells begin to produce
daughter-cells of only one kind. Growth of the embryo consists,
therefore, of the dissociation or division of the substance of the ovum
and blastomeres, followed by a gradually increasing differentiation of
the cells so produced.
Reintegration proceeds all the time. Blastula and gastrula larvæ are
really organisms capable of leading an independent existence--that
is, they are autonomous entities or individuals. The activities of
the parts of which they are composed--ectodermal locomotory cells,
ectodermal sensory cells, endodermal assimilatory cells, and so on,
must be co-ordinated. The cells are in organic material continuity with
each other, and events which occur in any one of them affect all the
rest. Impressions made upon the sensory cells are transmitted to the
locomotory cells, and food-material assimilated by the assimilatory
cells is distributed to all the others. At all stages the growing
embryo is an organic unity. The more fully it is developed, the greater
the morphological complexity of the organism, and the more numerous its
activities, the greater is the differentiation; but the greater also is
the co-ordination of the organs and tissues. In the higher animals this
co-ordination and integration of activities is effected (mainly) by the
central and peripheral nervous systems, but specially differentiated
nervous cells are not necessary for this purpose. Differentiation
during growth is therefore necessarily accompanied by reintegration of
the parts dissociated and differentiated.[27]
[27] Societies and civilisations, the associations of bees and ants,
or the Modern State, obviously exhibit this differentiation. It is
morphological and functional in the case of the Arthropods, since
individuals performing different duties are modified in form. It is
functional only in the case of human societies. Integration of the
activities of the individuals in both kinds of societies is effected
by inter-communication: articulate symbols in the case of the lower
animals, language in the case of man. If the concept of “orders of
individuality” were anything more than a convenient, though artificial,
analysis of naturally integral entities, we might speak of the ideal
state or the insect society as a “fourth order of individuality.”
In the process of organic growth the relation between mass and form
no longer holds in all the exactness with which it applies to the
growth of the crystal. We might spend a lifetime growing tablets of
cane-sugar, but in all cases we should find that the mass of any
crystal was proportional to the cube of a length of a diameter: there
would be a strict relation between mass and geometrical form. But this
strict relation does not hold in the case of a series of organisms
belonging to the same species but differing in size. If we measure,
for instance, the lengths of a great number of fishes of the same
species, we should find that we must describe the law of growth, not
by the simple equation _M_ = _al_^3, but by an empirically evaluated
expression of the form _M_ = _a_ + _bl_ + _cl_^2 + _dl_^3 + ... and
that the constants in this equation would vary with the species studied
and with the conditions in which it is living--that is, the organism
changes in form as it increases in size. This is inconceivable in the
case of purely physical growth by the accretion of molecules, and we
find again that the characters of the organism depend not only on what
it is but also upon what it has been--that is, upon its duration.
Growth, then, in plants and animals implies variability in form, in
general cumulative variability, leading to an indefinite departure from
the typical form.
The organism, therefore, does not grow simply by the accretion of
material, but, having attained a certain limit of size, it divides or
reproduces. In the lowest plants and animals this process of division
is simple: either the organism (unicellular or multicellular) divides
itself into two approximately equal parts or it divides into a number
of such parts. The first process is represented by the reproduction of
a bacterium or an _Amœba_, or by the division of a Planarian worm; the
second is represented by the division (in many Protozoa, for instance)
of the whole organism into a number of spores. Fundamentally the two
processes are alike: the simple, binary division of the Bacterium is
followed at once by growth by accretion, while in brood-formation (the
cases of multiple division) the parent cell divides, and then each of
the daughter-cells divide, and so on for several generations. After
the completion of these divisions the brood-cells grow by accretion
to their normal size. It is meaningless, in the light of our previous
discussion, to say that the individuality of the mother-cell “is
merged in that of the daughter-cells.” But we may believe that a
_Paramœcium_ possesses some degree of consciousness. Does it possess
personality--that is, the feeling of isolation from the rest of the
universe, and the feeling of oneness with its own past-memory or
conscious duration? If so, its personality, when it divides, becomes
one with that of its daughter-cells. Or is its personality and
conscious past that also of its sister-cells, and also that of the no
longer existent mother-cell, and the cell of which this in its turn was
a part? We must remember that such an organism as a _Paramœcium_ shows
in its behaviour most of the signs of intelligence; that the parts into
which it divides when it reproduces are equally developed; and that the
process of division may not interrupt the conscious duration of either
part. Is there a common personality, or oneness of consciousness,
of all the organisms of this kind which are descended from the same
individual?
Reproduction by division, simple or multiple, does not proceed
indefinitely in the case of the unicellular organisms. Sooner or later
there is a limit, and the cell is then no longer able to continue
dividing. Conjugation then occurs in one of many modes. Essentially two
organisms come into contact and their nuclei fuse, or rather some of
the material of one nucleus is transferred to the other. The cells then
separate and reproduction by division begins again.
This is not necessarily sexual reproduction: it is the conjugation
of essentially similar morphological entities. If two conjugating
_Paramœcia_ possessed distinct personalities we might imagine a
merging or addition of two conscious durations or memories. Sexuality,
however, includes less than this. In this mode of reproduction the
conjugating bodies are not organisms in the usual sense, but rather
modified organisms or highly modified parts of organisms. In some lower
plants the conjugating cells may be modified with respect to the cells
characteristic of the organism, but they may be approximately equal
in size. But in the multicellular plant and animal, in general, the
conjugates are cells detached from the parental body, and differing
chiefly from the cells of the latter in that they show a lack of
differentiation. One of these cells, that detached from the paternal
body, is the spermatozoon (in the case of the animal), or the pollen
cell (in the case of the plant). It is much smaller than the sexual
cell detached from the maternal body: this is the ovum in the case of
the animal, or the oosphere in the case of the plant. In general the
ovum is a relatively large cell, since it contains abundant cytoplasm,
which may also be loaded with yolk or other reserve food material.
The spermatozoon is very much smaller and consists of a nucleus with
a minimal mass of cytoplasm. The ovum is, in general, immobile; the
spermatozoon is generally highly mobile.
The essential process in the sexual reproduction of the unicellular
organisms is therefore the conjugation of the organisms themselves.
In multicellular organisms, modified cells--the germ-cells--become
detached from the bodies of the parents, and these cells conjugate.
In many lower plants and animals phases of sexual and asexual
reproduction alternate, thus _Paramœcium_ reproduces by simple
division, but at intervals conjugation occurs. In plants sporophytic
and gametophytic generations alternate, the sporophyte reproducing
by multiple division--that is, by the formation of spores, and the
gametophyte reproducing by the formation of germ-cells. There are few
organisms--possibly none--in which continued asexual reproduction by
simple or multiple division, spore-formation, bud-formation, etc., can
proceed without limit. In the great majority of cases investigated
asexual reproduction becomes feeble after a time and then ceases, and
it has been held that the stimulus of conjugation of the cells, or that
of sexual reproduction, is necessary for its renewal. In such cases
the organism is said to have become “senescent,” and “rejuvenescence”
by some means becomes necessary. As a general rule rejuvenescence is
effected by the interchange of nuclear matter between two conjugating
organisms, but it may be effected by rest, or by a change of
environment, or by the supply of some unusual food-material to the
liquid in which the dividing organism is contained. Thus, if various
materials be added to the water inhabited by a dividing _Paramœcium_,
the Protozoon may continue to reproduce by simple division for at least
two thousand generations. We must remember, however, that “senescence”
and “rejuvenescence” are only words; what is the essential nature of
the changes denoted by them we do not know.
In sexual reproduction, as it occurs in the great majority of
plants and animals, the ovum, or female germ-cell, is fertilised
or “activated” by the male germ-cell. But this activation by the
spermatozoon is not necessary, for the ovum itself is capable of
division and development to form a complete organism. This occurs
in the cases of natural parthenogenesis among insects and some
other animals, where the ovum proceeds, without fertilisation, to
segmentation and development. In some lower plants, where the size
of the male and female germ-cells is nearly equal, either of them
may undergo parthenogenetic development: in such cases we cannot, of
course, properly speak of sexual differentiation. In the cases of
organisms normally reproducing sexually, the stimulus to development is
afforded by the entrance into the ovum of the spermatozoon--that is,
by the mixture of the male and female germ-plasms; but in some animals
this stimulus may be replaced by the addition to the water in which
they are living of certain chemical substances. This is the process of
artificial parthenogenesis first studied by Loeb in the case of the
eggs of the Sea-urchin; and its analysis suggests that the spermatozoon
conveys some substance into the egg, and that this substance initiates
segmentation by setting up a train of chemical reactions. What
these reactions are exactly, and what is the process of “formative
stimulation” by the spermatozoon, we do not know. It is quite certain,
however, that much more than this process of formative stimulation
is involved in the fertilisation of the egg by the spermatozoon. The
mixture of the male and female germ-plasms resulting from conjugation
confers upon the embryo the characters of both the parents and of their
ancestries.
In an unicellular organism the “body” consists of a single cell
containing a nucleus. The extra-nuclear part of the cell--the
cytoplasm--is modified in various ways: thus it may possess flagella,
or cilia, so that it may be actively locomotory. It is at once a
receptor apparatus, susceptible to changes in the medium in which it
lives, and it is also an effector apparatus, capable of transforming
stimuli received into motor impulses. It may be able to accumulate
available energy by making use of the energy of radiation in the
synthesis of carbohydrate and proteid from the inorganic substances in
solution in the water in which it lives; and it is also able to expend
this energy in controlled movements. All the characteristics of life,
in fact, are exhibited by the unicellular organism, the differentiation
of the cytoplasm corresponding functionally to the differentiation of
the tissues of the multicellular animal or plant.
In the latter the organs, organ-systems, and tissues are composed of
differentiated cells. Development consists essentially of a process of
cell-formation by simple division, and at the end of this process of
segmentation various rudiments (Anlagen) are established. The older
embryologists sought to recognise the formation of three “germ-layers”
in most groups of animals: these were the outer layer or ectoderm,
the middle layer or mesoderm, and the internal layer or endoderm. The
ectoderm, it was held, gave rise to the integument, the central and
peripheral nervous systems, and the sensory organs. The mesoderm gave
rise to the musculature and skeleton, the excretory organs, and some
other tissues. The endoderm gave rise mainly to the alimentary canal
and its glands. The “Gastrea-Theory” of Haeckel sought to recognise
a similar larval form, or “Gastrea,” in the development of most
multicellular animals, and much ingenuity of argument was required for
the establishment of this homology. The newer embryology recognises
the difficulties implied in the application, in all its exclusiveness,
of the Gastrea-theory to the higher phyla of multicellular animals;
so that nowadays it has been necessary to abandon the notion of the
metazoan animal as being built up from these three primary germ-layers.
At the conclusion of segmentation, then, the embryo consists of a mass
of cells similar to each other in structure, but differing in fate
and in potency. Some of these cells are destined to give rise to the
integument, the nervous system, and the sense-organs; others become the
skeleton and musculature; and others again the organs of digestion,
assimilation, and excretion. A primary arrangement of these groups of
cells into three layers is indeed set up in many cases of development,
but it is plain that this arrangement is far from being an universal
one. Modern embryology shows in the clearest possible manner that at
the end of segmentation the embryo consists of a group of cells each
of which has normally a different fate in subsequent development. What
precisely each cell will become depends on its position with regard to
the others. But each cell is capable of becoming more than it normally
becomes: its potency is greater than its actual fate. If the normal
course of development is interrupted, a cell, which would usually have
given rise to a part of the skeleton, may give rise to a part of the
alimentary canal. The cells of the developing embryo are autonomous.
In the normal course of development most of the cells existing at the
end of segmentation give rise to the “body” of the organism, undergoing
differentiation as they so develop. But a few embryonic cells persist
without structural modification throughout the development of the
animal. They divide and grow and become greater in number, but
remain unchanged in other respects. These cells become the essential
reproductive organs, or gonads, of the adult animal--that is, the
ovaries of the female and the testes of the male. In the females of the
higher animals (the mammals, and perhaps some of the Arthropods) these
cells only divide and grow during the early stages of development, and
long before the beginning of adult life the number of ova in the gonads
has become fixed. In all males, and in the females of most animals,
however, the reproductive cells appear to be capable of unlimited
multiplication.
The essential cells of the gonads, the ovarian mother-cells or the
sperm mother-cells, constitute the germ-plasm. In modern, speculative,
biological literature the term germ-plasm is, however, restricted to
the chromatic material in the nuclei of the reproductive cells, the
cytoplasm being regarded as non-essential for the transmission of the
hereditary qualities of the organism. It seems clear, however, that
this distinction between the cytoplasm and the chromatic matter of
the nucleus is not always a valid one, so that it is best to speak of
the whole cell as constituting the germ-plasm. The embryonic cells,
therefore, have different fates: some of them become transformed
during development into the body or _soma_, and others remain
unmodified throughout life as the _germ_. The soma enters into intimate
relationships with the environment; it is affected by the vicissitudes
of the latter; and it may actively respond to them. The germ-cells may
possibly migrate through the body, perhaps, it has been suggested,
developing fatally and irresponsibly into the mysterious, malignant
tumours of adult life. Normally, however, they remain segregated in
the reproductive glands, secluded from the outer environment. Their
activities are inherent in themselves, are rhythmic, and become
functional only on the assumption by the soma of the phase of sexual
maturity. From the point of the species the soma is only the envelope
of the germ-cells. It is affected by every change of the environment,
and being usually cumulatively affected by the latter it becomes at
length an unfit envelope. Somatic death then follows as a natural
consummation, but the germ-cells are, in a sense, immortal in that they
remain capable of indefinite growth by division.
In the sexual reproduction of the higher organism a part of the
germ-plasm becomes detached, undergoes growth, and develops into an
organism exhibiting the parental organisation. But in the development
of the offspring, part of the germ-plasm received from the parent
persists unchanged, is transmitted to another generation, and so on
without apparent limit. _Something is transmitted from parent to
offspring._ This something we regard as a cell exhibiting a definite
chemical and physical structure; but while the germ-cell differs in
certain respects from an ordinary somatic cell, these structural and
chemical differences are insignificant when they are compared with
the differences in the potentialities of the cells. The somatic cells
are, in general, capable of reproducing only the general character of
the tissues of which they form part. Some of them, the cells of the
grey matter of the central nervous system, for instance, appear to be
incapable of division and growth. But again the facts of regeneration
appear to point to the possession by the somatic cells of more than
this restricted power of reproducing the tissues of which they form
part: to this extent the regeneration experiments tend to remove
the essential distinction between the somatic and germinal cells.
Neglecting these results in the meantime, we see that the germ-cells
contain within themselves the potentiality of reproducing the entire
organism in all its specificity. That which is transmitted from the
parent to the offspring is the parental organisation in all its
specificity; and to say that this organisation is a material thing is,
of course, to state a hypothesis, not a fact of observation.
This transmission of a specific form and mode of behaviour from
generation to generation is what a hypothesis of heredity attempts to
explain--that is, to describe in the simplest possible terms, making
use of the concepts of physical science. “Twelve years ago,” says
Jacques Loeb, “the field of heredity was the stamping ground for the
rhetorician and metaphysician; it is to-day perhaps the most exact and
rationalistic part of biology, where facts cannot only be predicted
qualitatively, but also quantitatively.” Let the reader examine
for himself the meagre array of facts on which this apotheosis of
mechanistic biology is based.
Two modern hypotheses of heredity demand attention--Weismann’s
hypothesis of the continuity of the germ-plasm, and Semon’s “Mnemic”
hypothesis. In the latter it is assumed that the basis of heredity
is the unconscious memory of the organism: modes of functioning are
“remembered” by the germ-plasm and are transmitted. This notion
presents many points of similarity to that which we consider later on,
so that it need only be mentioned here. Weismann’s hypothesis--like
Darwin’s hypothesis of Pangenesis--is a corpuscular one, and has
obviously been suggested by the modern development of the concepts of
molecules and atoms in the physical sciences. It supposes that that
which is handed down is a material substance of a definite chemical
and physical structure. This is not the germ-cell, nor even the nucleus
of the latter, but a certain material contained in the nucleus. The
latter contains protein substances containing a greater proportion of
phosphoric acid than does the cytoplasm of the cells in general; these
proteins are known as nucleo-proteins, though our knowledge of their
chemical structure is, so far, not very exact. It is not, however,
these that are the germ-plasm, but a substance in the nucleus _which
becomes visible when the cell is killed in certain ways, and which
becomes stained by certain basic dyes_. It is distinguished by this
character alone and on that account is loosely called “chromatin.” This
substance Weismann identifies as “the material basis of inheritance.”
When a cell divides, a very complex train of events usually occurs.
This process of “Mitosis” exhibits many variations of detail, and
without actual demonstration it is rather difficult to explain clearly.
But its essential feature is evidently the exact halving of all the
structures in the cell which is about to divide. In the ordinary cell
which is not going to divide immediately, the chromatin is diffused
throughout the nucleus as very numerous fine granules, recognised only
by their staining reactions. They may be concentrated at some part of
the nucleus, so that a division through a plane of geometrical symmetry
of the cell would not, in general, exactly halve the chromatin. Prior
to division, therefore, this substance becomes aggregated as granules
lying along a convoluted filament of a substance called “linin,” which
is characterised principally by the fact that _it does not stain with
the dyes that stain the chromatin_. The filament breaks up into short
rods, called Chromosomes, and these rods become arranged in the equator
of the nucleus. The rods then split longitudinally, and one-half of
each moves towards one pole of the nucleus, the other half moving
towards the other pole. Various other modifications of the cell and
nucleus occur concomitantly with these changes, but the essential thing
that happens seems to be the halving of all the structures of the cell,
and this is the simplest explanation of the phenomena of mitotic cell
division. Two daughter-cells are then formed by the division of the
mother-cell, and each of these daughter-cells receives one-half of each
of the chromatin granules that were contained in the mother-cell.
The chromosomes, or “Idants,” are seen to consist of discrete granules,
and these are (generally) the bodies known as the “Ids.” The id
cannot be resolved by the microscope into any smaller structures: it
lies on the limits of aided vision; but the hypothesis assumes that
it is composed of parts called “Determinants,” and the determinants
are further supposed to consist of “Biophors.” The biophors are the
ultimate organic units or elements, and they are of the same order
of magnitude as chemical molecules. We must suppose them to be more
complex than a protein molecule, and the latter contains many hundreds
(at least) of chemical atoms. Now it is possible to calculate the
number of atoms contained in a particle of the same size as the id:
such a calculation may be made by different methods, all of them
yielding concordant results. This calculated number of atoms may be
less than that which we must suppose to be present in the biophors, of
which the hypothetical id is composed![28]
[28] “But,” says Weismann, referring to an objection of this nature,
“it should rather be asked whether the size of the atoms and molecules
is a fact, and not rather the very questionable result of an uncertain
method of investigation.”
The id is supposed to contain all the potentialities of the
completely developed organism. It is composed of a definite number of
determinants, each of the latter being a “factor” for some definite,
material constituent of the adult body. There would be a determinant
for each _kind_ of cell in the retina of the eye, one for the lens,
one for the cornea (or rather for each kind of tissue in the latter),
one for each kind of pigment in the choroid and iris, and so on;
every particular kind of tissue in the body would be represented by
a determinant. Thus packed away in a particle which lies just on the
limits of microscopic vision are representatives of all those parts
of the body which are chemically and physically individualised, each
of these hypothetical “factors” being a very complex assemblage of
chemical atoms. In development the determinants become separated from
each other, so that whatever parts of the body are formed by the first
two blastomeres are represented by determinants which are contained in
those cells, and which are sifted out from each other and segregated.
As development proceeds this process of sifting becomes finer and
finer, until when the rudiments of each kind of tissue have been laid
down a cell contains only one kind of determinant. This consists of
biophors of a special kind, and the latter then migrate out from the
chromatin into the cytoplasm of the cells in which they are contained,
and proceed to build up the particular kind of tissue required.
The nucleus of the germ-cell is thus a mixture of incredible
complexity, but in addition to this material mixture there must exist
in it the means for the _arrangement_ of the determinants in the
positions relative to each other occupied by the adult organs and
tissues. A mechanism of unimaginable complexity would be required for
this purpose, and it must be a mechanism involving only known chemical
and physical factors. It is safe to say that absolutely no hint as to
the nature of this mechanism is contained in the hypothesis.
The determinants must be able to grow by reproduction, or by the
accretion of new biophors, since in each generation new germ-cells are
formed. If we say that they grow by reproduction in the sense that an
organism grows by reproduction, we beg the question of their means
of formation. Do they grow by the addition of similar substances in
the way that a crystal grows? If so, the molecules of which they are
composed must exist in the lymph stream bathing the germ-cells--that
is, the biophors themselves must already exist in this liquid, for if
we suppose that the biophors are able to divide and grow by making
use of the protein substances which we know are present in the lymph
stream, then we confer upon these bodies all the properties of the
fully developed organism. If they are present in the blood, then the
composition of the latter must be one of inconceivable complexity,
since it must contain as many substances as there are distinct tissues
in the animal body. We know, of course, that this is not the case. How,
then, are the biophors reproduced?
We must leave this field of unbridled speculation (which cannot surely
be “the most exact and rationalistic part of biology.”) What the study
of the reproduction of the organism does show is that something--which
we call the specific organisation--is handed down from parent to
offspring, and that this something _may_ possess a high degree of
stability. No apparent change of significance can be observed in
the very numerous generation of organisms (the 2000 generations of
_Paramœcium_, for instance, which were bred by Woodruff) which can
be produced by experimental breeding. Some species of animals--the
Brachiopod _Lingula_, for instance--have persisted unchanged since
Palæozoic times. Throughout the incredibly numerous generations
represented by this animal series, the specific organisation must have
been transmitted in an almost absolutely unchanged condition. The
germ-plasm is therefore continuous from generation to generation, and
it possesses an exceedingly great degree of constancy of character.
This conception of the continuity and stability of the specific
organisation is the feature of value in Weismannism, and all that
we know of the phenomena of heredity confirms it. But it is pure
speculation to regard the organisation as an aggregate of chemically
distinct substances, or if we say that this speculation is rather a
working hypothesis, then it must justify itself by leading us back
again to the results of experience.
It is, however, not quite accurate to say that the organisation
persists unchanged from generation to generation. The offspring is
similar to the parent--that is, the organisation has been transmitted
unchanged. But the offspring also differs just a little from the
parent--that is to say, the organisation is modified by each
transmission. In these two statements we formulate in the simplest
manner the law of organic variability. Organisms may obviously be
arranged in categories in such a way that the individuals in any one
category resemble each other more closely than they resemble the
individuals belonging to another category. We may, by experimental
breeding, produce an assemblage of organisms all of which have had
a common ancestor, or a pair of ancestors. Now the individuals
composing such an assemblage would exhibit a close resemblance
to each other, such a resemblance as our categories of naturally
occurring organisms are seen to exhibit. We should also find that the
individuals of our naturally occurring assemblage would be able to
interbreed among themselves, just as in the case of the experimentally
produced population. It may be concluded, then, that the naturally
occurring population is also the product of a pair of ancestors. This
inter-fertility, as well as the close morphological resemblance of the
individuals, are the facts on which the hypothesis of the common origin
and unity of the assemblage, or species, is formed.
The morphological resemblance between the individuals, either in
the natural or the artificial populations, is not absolute. If we
take any single character capable of measurement we shall find that
it is variable from organism to organism. This important concept of
organic variability may be made more clear by a concrete example.
Examination of a large number of cockle shells taken from the same
restricted part of the sea-shore, and therefore belonging presumably
to the same race, will show that the number of the radiating ridges
on the shell varies from 19 to 27, and that the ratio of the length
to the depth of the shell also varies from 1 : 0.59 to 1 : 0.85. In
the former case the most common number of ridges is 23, and in the
latter case the most common ratio of length to depth is 1 : 0.71.
These are the characteristic or modal values of the morphological
characters in question, and the other or less commonly occurring
values are distributed symmetrically on either side of the mean or
modal value, forming “frequency distributions.”[29] The value of
the first character changes by unity in any distribution: obviously
there cannot be a fraction of a ridge; and this kind of variation is
called “discontinuous.” The value of the second character may change
imperceptibly, and it is therefore called “continuous,” a term which
is not strictly accurate, since in applying it we assume that the
numerical difference between two variates may be less than any finite
number, however small. In this assumption we postulate for biology the
distinctive mathematical concept of infinite divisibility.
[29] See Appendix, p. 350.
The difference from the mode, or mean, with respect to a definite
character in a fully grown organism may be due to the direct action of
the environment, in the sense in which we have regarded the environment
as influencing the organism; or it may be due to the changes in the
organism resulting from the increased or decreased use of some of its
parts. The conditions with regard to nutrition, for instance, will not
be the same for all the individuals composing a cluster of mussels
growing on the sea-bottom. Those in the interior of the cluster do not
receive so abundant a supply of sea-water as those on the outside of
the cluster; and since the amount of food received by any individual
depends on the quantity of water streaming over it in unit time, we
shall find that the internally situated individuals will be stunted
or dwarfed, while those on the outside will be well grown. Such
variations are acquired ones, but even when we allow for them, even
if we take care that all the organisms studied live under conditions
which are as nearly uniform as possible, there will still be some
degree of variability. We cannot be sure that this absolute uniformity
ever exists; and the notion of the environment of an organism may be
extended so as to include the medium in which embryonic development
took place, and even the parental body which formed the environment
for the germ-cells from which embryonic development began. But it is
probably the case that even with an uniform environment, or with one
in which the differences were insignificant, variability would still
exist. The variations that might be observed in such a case would
belong to two kinds--“fluctuating variations,” and “mutations.”
[Illustration: FIG. 21.]
Whether the variations observed in a population of organisms are
fluctuations or mutations can only be determined by experiment.
Let us suppose that we are dealing with a human population, and
that the variation studied is that of stature. Let the men with
statures considerably over the mean value marry the women who are
correspondingly tall, then it will be found that the children from
these unions will, when grown up, exhibit a stature which is greater
than that of the whole population, but not so great as that of their
parents--that is, regression towards the mean of the whole population
takes place.
This is shown in the above diagram, where the lines above and below
the mean one indicate the proportion (relative to the value or
frequency of the mean) of people of each grade of stature. The latter
is proportional to the distance from the mean measured along the
vertical line, distances below this line indicating statures below the
mean, and _vice versa_.
If, on the other hand, the men and women with statures considerably
below the mean marry, their children will ultimately exhibit statures
which are greater than that of their parents, but which are less than
that of the whole population. Regression again occurs, but in the
opposite direction, and such a case would be represented by the above
diagram reversed. Continued selection of this kind would lead to an
immediate increase in the mean stature (or the opposite, if the “sign”
of the selection were reversed) in one or two generations, but after
that the amount of change would be very small, while if the selection
were to cease the race produced would slowly revert to the mean, which
is characteristic of the whole population from which it arose. It is
very important to grasp this result of the practical and theoretical
study of heredity--the selection of the ordinary variations shown by a
general population leads at once to a small change in the mean value
of the character which is selected, but continued selection thereafter
makes very little difference to this result, while the race slowly
reverts to the value of that from which it arose on the cessation of
the selection.
Races which “breed true” do, of course, exist; thus the mean height of
the Galloway peasant is greater than that of the Welsh. In the cases
of “pure races”--that is, races which breed true with respect to one
or more characters, we have to deal with another kind of variation,
one which shows no tendency to revert to the value from which it
arose. Let the observed variability of stature in a human population be
represented by the frequency distribution _A_, and let the individuals
at _N_--that is, those in which the stature was greater than the mean
by the deviation _ON_--intermarry. It might then happen that the
variability of the offspring of these unions would be represented by
the frequency distribution _B_, in which the value of the mean is also
that of the stock, at _N_, from which the race originated. It does not
matter now from what variants in _B_ a progeny of the third generation
arises: the mean height of the latter will be that of the pure race. In
this case the individuals from which the pure race originated (those at
_N_ in _A_) have exhibited a mutation. The stature of the individuals
of this new race will continue to exhibit fluctuating variations, and
the range of this variability may be as much as that of the stock from
which it arose, _but the mean stature of the new race_ will continue to
be that of the original mutants.
[Illustration: FIG. 22.]
It is well known that de Vries himself considered fluctuating
variations and mutations as something quite different. The former he
considered as nothing new, only as augmentations or diminutions of
something previously existing; and he regarded fluctuations as due to
the action of the environment, following in their distribution the laws
of chance.[30] Mutations, on the other hand, were something quite new.
Now future analysis of variability will not, we think, bear out the
validity of this distinction. It is far more likely that a fluctuation
is a variation which is the result of some causes the action of
which is variable. (We are regarding variability now as subject to
“causation” in the physical sense, for only by so regarding it can we
attempt its analysis). As a rule this process results in a fluctuation,
but if its extent, or degree of operation, exceeds a certain “critical
value” a mutation is produced. We may, following the example of the
physicists, illustrate this by a “model.”
[30] See Appendix, p. 351.
[Illustration: FIG. 23.]
This model is a modification of Galton’s illustration of the degrees of
stability of a species. It is a disc of wood rolling on its periphery.
We divide it into sectors, and the arcs _ab_, _cd_, _ef_, and _gh_ have
all the same radius, 10, 20, 30, and 40. Then we flatten the sectors
_bc_, _de_, _fg_, and _ha_, so that their radii are greater than are
those of the other arcs. Now let us cause the disc to roll about the
point 8 as a centre. It will oscillate backwards and forwards about a
mean position 8. Let us think of these oscillations as fluctuations.
Suppose, however, that we cause the disc to roll a little more
violently, so that it oscillates until either of the points 3 or
4 are perpendicularly beneath the centre _O_. In either of these
positions the disc is in a condition of “unstable equilibrium,” and an
infinitesimal increase in the extent of an oscillation will cause it
to roll beyond the points 3 or 4. But if it does pass either of these
critical points it will begin to oscillate about either of the new
centres 5 or 7, thus rolling on one of the arcs, _ha_ or _de_. This
assumption of a new condition of stability we may compare with the
formation of a mutation.
All this is merely a conceptual physical model of a process about which
we know nothing at all. It is meant to illustrate the view that the
organisation of a plant or animal is not something absolutely fixed and
invariable. The organism in respect of each recognisable and measurable
character oscillates about a point of stability, that is to say
exhibits fluctuating variations about the mean value of this character.
If the stability of the organisation is upset, so that it oscillates,
or fluctuates about a new centre, that is, if the variations deviate
in either direction from a new “type” or mean, a mutation has been
established. A mutation is not, therefore, necessarily a large
departure from “normality.” It is not necessarily a “discontinuous
variation,” nor a “sport” nor a “freak.” It is essentially a shifting
of the mean position about which the variations exhibited by the
organism fluctuate.
Such a mutation will, in general, involve the creation of an
“elementary species.” We have considered only one character, say
stature, in the above discussion, but it generally happens that the
assumption of a new centre of stability involves _all_ the characters
of the mutating organism. An elementary species therefore differs a
little in respect of all its characters from the species from which it
arose, or from the other elementary species near which it is situated.
This is what we do usually find in the cases of the “races,” or “local
varieties,” of any one common species of plant or animal. That we
do not recognise that most, or perhaps all, of the species known to
systematic biology are really composed of such local races is merely
because such results involve an amount of close investigation such as
has not generally been possible except in the few cases studied with
the object of proving such variability; or in the case of those species
which are studied with great attention to detail because of their
economic importance. Thus the herrings of North European seas can be
divided into such races, and it is possible for a person possessing
great familiarity with these fishes to identify the various races or
elementary species--that is, to name the locality from which the fish
were taken--by considering the characteristics in respect of which the
herrings of one part of the sea differ from those of other parts.
The term “variety” has rather a different connotation in systematic
biology from that which is included by the term “elementary species.”
The meaning of the latter is simple and clear. Two or more elementary
species are assemblages of organisms, in each of which assemblages
the mean positions about which the various characters fluctuate is
different. The term “variety” cannot so easily be defined. The progeny
of two different species (in the sense of the term as it is usually
applied by systematists) may be called a hybrid variety of one or other
of the parent species. In the case of the ordinary species of zoology
such a hybrid would, in general, be infertile, or if it did produce
offspring these would be infertile. In the case of ordinarily bred
offspring from parents of the same species a large deviation from the
parental characters might be a malformation, or the result of some
irregularity of development. An “atavistic” variation we may regard as
the reappearance of some character present in a more or less remote
ancestor. Thus dogfishes and skates are no doubt descended from some
elasmobranch fish which possessed an anterior dorsal fin. This fin
persists in the dog-fishes, but has been lost in the skates and rays.
Yet it may appear in the latter fishes as an atavistic variation.
In a variety (following de Vries’ analysis) a character which
disappears is not really lost: it is only suppressed, and it still
exists in a latent form. Some flowers are coloured, for instance, but
there may be varieties in the species to which they belong in which the
flowers are colourless. It may not be quite correct, in the physical
sense, to say that the colour has been lost, but we may put it in this
way. These flowers are then coloured and colourless varieties of the
same species. Colour or lack of colour is not, however, fixed in the
variety, for the individual plant bearing colourless flowers also bears
in its organisation the potentiality of producing coloured flowers.
The petals of a flower may be smooth or covered with hairs, and in the
same stock both of these varieties may occur. But we must not speak
of the presence or absence of hairs as constituting a difference of
kind: the smooth-petalled flowers might be regarded as containing the
epidermal rudiments of hairs. So also coloured and colourless flowers
may be regarded as containing the same kinds of pigment, but these
pigments are mixed in different proportions. Such a view enables us to
look upon these contrasting characters in the same way as we look upon
fluctuating variations, that is, as quantitative differences in the
value of the same character.
Such a suppression of a character is not really a loss. An organism
belonging to an elementary species in which, say, monochromatic flowers
are usually produced may produce flowers which are striped. The progeny
of the plant may still produce monochromatic flowers, but we must
think of it as also possessing the potentiality of producing striped
flowers. In the terminology of Mendelism the characters are dominant
and recessive ones.
In discussing Mendelian varieties we consider the manner in which two
contrasting characters--one present in the male parent and one in the
female--are transmitted to the offspring. The characters in question
may be the tallness of the male parent and the contrasting shortness
of the female; or the brown eyes of the male and the blue eyes of the
female; or the brown skin of the female parent and the white skin of
the male one. These characters may be inherited in two ways: either
they may be blended or they may remain distinct in the offspring. The
children of the brown mother and the white father are usually coloured
in some tint intermediate between those of the parents. The mulatto
hybrid is fertile with either of the parent races, and again the
offspring may take a tint intermediate between those of the parents,
and so on through a number of generations. But somewhere in this
series the concealed or recessive brown colour may appear in all its
completeness, showing that it has been present in the organisations
of all the intervening generations. The progeny of a tall male parent
and a short female parent are not, in general, intermediate in stature
between the parents; some of them may be tall and others short. The
children of a brown-eyed mother and a blue-eyed father do not usually
have eyes in which the colours of the parental eyes are blended: they
are blue-eyed or brown-eyed. The contrasting characters are spoken of
as dominant and recessive: if tallness is transmitted to offspring,
which may nevertheless produce dwarf offspring, the latter character
is said to be recessive to tallness. The contrasting characters of the
parents therefore remain distinct in the progeny, some of the latter
exhibiting the one character and some the other; while it may happen
that the one character or the other may be segregated, so that it only
appears in, and is transmitted by, the offspring. There are numerical
relationships between the numbers of the offspring in which the
contrasting characters appear.
Obviously, tallness and dwarfness are not characters which differ in
_quality_: they are different degrees of the same thing. Brown eyes
and blue eyes are not necessarily different in quality, for we may
think of the same kinds of pigment as being present in the iris but
mixed in different proportions. But the terminology of this branch of
biology appears to suggest that the contrasting characters are, each
of them, something quite different from the other: there are “factors”
for “tallness,” “dwarfness,” for blue eyes and brown eyes, and so on.
These qualities are called “unit-characters,” and they are supposed to
possess much the same individuality in the germ-plasm as the “radicles”
of the chemist possess in a compound. Sodium chloride, for instance,
is not a blend of sodium and chlorine: the two kinds of atoms do not
fuse together but are held together merely. The analogy is, however,
very imperfect, for in the chemical molecule the characters are not
those of either of the constituents but something quite different,
whereas in the Mendelian cross the characters remain distinct, but one
of them is patent while the other is latent. In the molecule, however,
the atoms are regarded by the chemist as lying beside each other in
certain positions, and the Mendelian factors are also spoken of as if
they lay side by side in the germ-plasm. This terminology is useful,
perhaps necessary, in the work of investigation, but we must not forget
that it symbolises, rather than describes, the results of experiment.
If the factors are identified with certain morphological structures
in the nuclei of the germ-cells, obviously all the objections that
may be urged against the Weismannian hypothesis as an hypothesis of
development apply also to the Mendelian hypotheses as descriptions of a
physical process of the transmission of morphological characters.
It should clearly be understood what is implied in the construction of
such a hypothesis. Certain processes are observed to take place when a
somatic cell divides: these processes we have regarded as having for
their object the exact division of all the parts of the cell into two
halves. This process of somatic cell division is modified when a germ
cell divides prior to maturation (the process fitting it to become
fertilised). Then the cell nucleus divides into four daughter-nuclei.
One of these remains in the cell substance which is to become the ovum,
and the other three, each of them invested in a minimal quantity of
cytoplasm, are eliminated as the “polar bodies.” Also the number of
chromosomes in the mother-cell becomes halved, so that the mature ovum,
or spermatozoon, possesses only one-half of the number of chromosomes
which are present in the ordinary somatic cell. Now let the reader
puzzle out for himself what may be meant by this behaviour of the
germ cells, and he will certainly see that several interpretations are
possible. But suppose that the chromatin consists of an incredibly
large number of bodies differing in chemical structure from each
other, and occupying definite positions with regard to each other;
and suppose that there is a mechanism of unimaginable complexity in
the cell capable of rejecting some of these chemically individualised
parts, and of “assembling” or arranging the others in much the same way
as an engineer assembles the parts of a dynamo when he completes the
machine. _Then_ we may regard the hypothetical discrete bodies which
form the hypothetical nuclear architecture as the material carriers of
Mendelian characters. It is strange that the correspondence of such a
logically constructed mechanism with the effects which it would produce
if it existed should be regarded as a proof that it does exist, yet
biological speculation has actually made use of such an argument. “It
seems exceedingly unlikely that a mechanism so exactly adapted to
bring it” (the separation from each other of the Mendelian material
“factors” of inheritance) “about should be found in every developing
germ cell if it had no connection with the segregation of characters
that is observed in experimental breeding.” Put quite plainly this
argument is as follows: there is a certain segregation to be seen
in experimental breeding, and certain processes may be observed to
occur in the developing germ cell. Add to these processes many others
logically conceivable, and add to the observed material structure of
the cell another structure also logically conceivable. Then the assumed
mechanism and structure is “exactly adapted” to produce the effects
which are to be explained. Therefore the mechanism and structure do
actually exist!
That which renders the son similar to the father--the specific
organisation--is undoubtedly very stable, and it may persist in the
face of a variable environment. But now and then the son differs
from the father. The differences may be “accidental” and may not be
transmitted further--then we have to deal with an unstable fluctuation;
or the differences may be permanent--then we have to deal with a stable
mutation. What “produces” a mutation? A change of the environment, it
may be said: if so, the mutation is an active change or adaptation of
the organism to a change in its surroundings, and this adaptation is a
permanent one and is transmitted. Or the mutation may be a spontaneous
change of functioning. If this disturbance of the stability of the
organisation is _general_, if it affects all the characters of the
organism, we have to deal with the establishment of a new elementary
species. But if the disturbance affects only one, or a few characters,
then we need not recognise that a new elementary species has come into
existence. Men and women remain men and women (in their morphology),
although some time or other among the brown eyes characteristic of a
race blue eyes may have appeared. The result of the disturbance, in
this case, has been to cause one, or a few, of the characters that
fluctuate to surpass their limits of stability.
The idea of the elementary species is a clear and simple one. It is
a group of organisms connected by ties of blood relationship: all
have descended from one pair of ancestors. The individuals exhibit
certain characters, all of which are variable. This variability is
not cumulative; in generation after generation the individuals of
the species display variations which fluctuate round the same mean
values. Two or more elementary species may have had the same origin--a
common ancestor or ancestors--but the organisms in one species exhibit
characters which, although similar in nature to those of the other
species, yet fluctuate about different mean values.
This is not the “species” of the systematic biologist. The Linnean or
systematic species is a concept which is much more difficult to define:
it is a concept indeed which has not any clear and definite meaning, in
actual practice.
We often forget how very young the science of systematic biology
is, and how intimately its progress has been dependent on that of
human invention and industrial enterprise. Physics and mathematics
might be studied in a monastic cell, but the study of systematic
biology can only be carried on when we have ships and other means of
travelling--the means, in short, of collecting the animals and plants
inhabiting all the parts of the earth’s surface. Until a comparatively
few years ago the fauna and flora of great tracts of land and sea were
almost unknown: even now our knowledge of the life of many parts of the
earth is scanty and inaccurate. Systematic biology has therefore had to
collect and describe the organisms of the earth, and in so doing it has
set up the Linnean species of plants and animals. These we may describe
as, in the main, categories of morphological structures. The older and
more familiar species are clearly defined in this respect: such are
cats and dogs, rabbits, tigers, herrings, lobsters, oysters, and so
on: the individuals in each of these categories are clearly marked out
with respect to their morphology, and the limits of the categories are
clearly defined. In all of them the specific organisation has attained
a high degree of stability so that the individuals “breed true to
type”; and it has also attained a high degree of specialisation, so
that it does not fuse with other organisations.
Yet, in the majority of the systematic species of biology, this
criterion of specific individuality--this recognition of the isolation
of the species from other species--cannot be applied. Very many species
have been described from a few specimens only, many from only one. How
does a systematist recognise that an organism with which he is dealing
has not already been classified? It differs from all other organisms
most like it, that is, he cannot identify it with any known specific
description. But the differences may be very small, and if he had a
number of specimens of the species most nearly resembling it he might
find that these differences were less than the limits of variation in
this most closely allied species, and he would then relegate it to
this category. But if he has to compare his specimen with the “type”
one, that is, the only existing specimen on which the species of
comparison was founded, the test would be unavailable. The question to
be answered is this: are the difference or differences to be regarded
as fluctuations, or are they of “specific rank”? Now certainly many
systematists of great experience possess this power of judgment, though
they might be embarrassed by having to state clearly what were the
grounds on which their judgment was based. But on the other hand hosts
of species have been made by workers who did not possess this quality
of judgment; and even with the great systematists of biology confusion
has originated. Slowly, very slowly, the organic world is becoming
better known, and this confusion is disappearing.
The species, then, whether it is the systematic group of the biological
systems, or the elementary species based on the study of variability
and inheritance, is an intellectual construction: an artifice designed
to facilitate our description of nature. This is clearly the case with
the higher orders of groups in classifications: genera, families,
orders, classes, and phyla express logical relationships, or describe
in a hypothetical form our notions of an evolutionary process. But
species, it may be said, have an actual reality: there are no genera in
nature, only species. These categories of organisms really exist; they
have individuality, a certain kind of organic unity, inasmuch as the
individuals composing them have descended from a common ancestor. Yet
just as much may be said of genera, families, and the other groupings.
One species originates from another by a process of transmutation:
a genus is a group of species which have all had a common origin; a
family is a similarly related group of genera, and so on. The higher
categories of biological science are intended to introduce order and
simplification into the confusion and richness of nature as we observe
it, but obviously the concept of the species has the same practical
object. Must we then say that there are no species in nature, only
individuals? If so, we are at once embarrassed by the difficulty of
forming a clear notion of what is meant by organic individuality. Does
it not indicate that life on the earth is really integral, and that our
analysis of its forms--species, genera, families, and so on--are only
convenient ways of dealing actively with all its richness?
Systematic biology is a very matter-of-fact occupation, and one is
surprised to find upon reflection how he, in his handling of the
concepts of the science, follows the methods of ancient philosophy.
In classical metaphysical systems mutability was an illusion. Behind
the confusion and change given to sensation there is something that
is immutable and eternal. If there is change there is something that
changes; or, at least there ought to be something that changes when it
is perceived through the mists of sensation, just as the image of a
well-known object on the horizon wavers and is distorted by refraction.
This immutable reality is the Form or Essence of the Platonic Idea:
that which is in some way degraded by its projection into materiality,
so that we become aware of it only through our imperfect organs of
sense. We do not see the Form itself, but its quality rather, the Form
with something added or something taken away from it.
The Form itself is only a phase in a process of transmutation.
Everything that exists in time flows or passes into something else.
But it is not a momentary or instantaneous view of the flux that we
see, but rather a certain aspect of the reality that flows, that in
some way expresses the nature of the transmutation from one Form
into another. The sculptor represents the motion of a man running by
symbolising in one attitude all the actions of body and limbs; so that
from our actual, sensible experience or intuition of the movement of
the runner we see in the rigid marble all the plasticity of life. The
instantaneous photograph shows us a momentary fixed attitude of the
runner--an attitude which is strange and unfamiliar. The Idea does not,
then, represent a moment of becoming like the photograph, but rather a
typical or essential phase of the process of transmutation, just as the
sculptor represents in immobile form the characteristic leap forward of
the runner. Just as our intuitive knowledge of the actions of our own
bodies enables us to read into the characteristic attitude represented
in the marble all the other attitudes of the series of movements, so
our experience enables us to expand the formal moment of becoming into
the action which it symbolises.
This action has a purpose, an intention or design which was
contemplated before it began. There is therefore the threefold meaning
in the Platonic Idea: (1) an immutable and essential Form of which
we perceive only the quality; (2) the characteristic phase in the
transmutation of this Form into some other one; and (3) the design or
intention of the transmutation.
This was, as Bergson says, the natural metaphysics of the intellect.
It was, in reality, the “practical” way of introducing order and
simplification into the confusion of the sensible world--all that is
presented to us by our intuitions. And in the effort to reduce to order
the welter of the organic world biology has followed the same method,
so that it represents the species with the threefold significance of
the Platonic Idea. That which is expressed in the term species is
an assemblage of organisms each of which is defined by an essential
form and an essential mode of behaviour--the characters indicated in
the specific diagnosis. But organisms are variable, their specific
characters fluctuate round a mean, and in saying this we suggest that
there is something which varies--there _ought to be_ an essential form
from which the observed forms of the individuals deviate, something
invariable which nevertheless varies accidentally. This is (1) the
quality of the specific idea. So also we never do actually observe
the essential individual; what we do see is the embryo, or the young
and sexually immature organism, or the sexually mature one, or the
senescent one: there is continual change from the time of birth to
that of senile decay. This confusion is unmanageable, and for it we
substitute the characteristic form and functioning, and that phase in
the life-history of the organism which suggests all that the previous
phases have led up to, and all that subsequent phases take away. Thus
there is contained in our idea of the species (2) the notion of a
typical moment in an individual transformation. It is not a “snap-shot”
of some moment in the life-history that we make: in identifying a
larval form as some species of animal we are identifying it with all
the other phases of the life-history.
Since we accept the doctrine of transformism, the specific idea also
includes that of an evolutionary process. For the organic world is
a flux of becoming, and species are only moments in this becoming.
It does not help us to reflect that if the hypothesis of evolution
by mutations is true the process is a discontinuous one: mutability
is the result of periods of immutability during which the change was
germinating, so to speak. In this flux of becoming we seize moments at
which the specific form flashes out--not as instantaneous views of the
flux, but as aspects of it which suggest the steps, the morphological
processes, by which the transmutation of the species has been effected.
Thus our specific idea represents not only a phase of becoming in
an individual life-history, but also a phase of becoming in an
evolutionary history.
Whether we consider this evolutionary movement as the working out of a
Creative Thought, or as the development of elements assembled together
by design, or as the results of the action of a mechanism working by
itself, we must suppose that underlying it there is design, or purpose,
or determinism. All is given, therefore, and our comparison between
the metaphysical Platonic Idea and the modern concept of the species
becomes complete.
CHAPTER VI
TRANSFORMISM
The species is therefore a group of organisms all of which exhibit
the same morphological characters. This sameness is not absolute, for
the individuals composing the species may vary from each other with
respect to any one character. But the range of these variations is
limited. They fluctuate about an imaginary mean value which remains
constant in the case of a species which is not undergoing selection,
and is therefore nearly the same throughout a series of generations.
The formal characters which we regard as diagnostic of the species are
these imaginary mean ones.
It is possible to breed from stock a very great number of animals, all
of which are connected by a tie of blood-relationship, that is, all
have descended from the same ancestor or ancestors. Such an assemblage
of animals would resemble those assemblages living in the wild which
we call species, in that a certain morphological similarity would be
exhibited by all the individuals. If the breeding were conducted so as
to avoid selection, the range of variability would be very much the
same as that observed in the wild race. The two groups of animals--that
bred artificially, and that observed in natural conditions--would be
very much alike, and it is impossible to resist the conclusion that the
natural race, like the artificial one, is a family in the human sense,
that is, all the individuals composing it are connected together by a
tie of common descent.
Let us extend this reasoning to categories of organisms of higher
orders than species. We can associate together groups of species in
the same way that we associate together the individuals of the same
species. There are certain morphological characters which are common
to all the species in the category, but there are also differences
between specific group and specific group, and these differences may
be regarded as variations from the generic morphological type. All
the Cats, for instance, have certain characters in common: fully
retractile claws, a certain kind of dentition, certain cranial
characters, and so on. We postulate a feline type of structure, and
we then regard the characters displayed by the cat, lion, tiger,
leopard, etc., as deviations from this feline morphological type. Thus
we establish the Family Felidæ. But again we find that the Felidæ
together with the Canidæ, and many other species of animals, also
display common characters, dental and osteological chiefly, and we
express this resemblance by assembling all these families in one Order,
the Carnivora. The Carnivores, however, are only one large group of
Quadrupeds: there are many others, such as the Rodents, Ungulates,
Cetacea, etc., and all of these possess common characters. In all
of them the integument is provided with hairs, or other similarly
developed structures; all breathe by means of a diaphragm; in all,
the young are nourished by suckling the mammæ of the mother; and
all develop on a placenta. We therefore group them all in the Class
Mammalia. Now the Mammals possess an internal skeleton of which the
most fundamental part is an axial rod--the notochord--developing
to form a vertebral column; and this notochordal skeleton is also
possessed by the Birds, Reptiles, Amphibia, and Fishes. There are
also some smaller groups in which the notochord is present but does
not develop to form segmented vertebræ. Including these, we are able
to form a large category of animals--the Chordata--and this phylum is
sharply distinguished from all other cognate groups.
All animals and plants may be classified in a similar way. Insects,
Spiders, and Crustacea, for instance, are all animals in which the
body is jointed, each joint or segment being typically provided with
a pair of jointed appendages or limbs. Because of this similarity of
fundamental structure we include all these animals, with some others,
in one phylum, the Arthropoda. So also with the rest of the animal
kingdom, and similar methods may be extended to the classification of
the plants. A few small groups in each of the kingdoms are difficult to
classify, but it has been possible to arrange most living organisms in
a small number of sub-kingdoms or phyla, and even to attempt to trace
relationships between these various categories.
The mere systematic description of the organic world would have
resulted in such a reasoned classification apart altogether from any
notions of an evolutionary process. But the classification, originally
a conventional way of making a list of organisms, would at once
suggest morphological similarities. It would suggest that all the
Cats were Carnivores, that all the Carnivores were Mammals, and that
all the Mammals were Chordates. It would suggest that all Wasps were
Hymenoptera, that all Hymenoptera were Insects, and that all Insects
were Arthropods. It would establish a host of _logical_ relations
between animals of all kinds.
It would show us a number of groups of animals separated from each
other by morphological dissimilarities. But let us also consider all
those animals which lived in the past of the earth, and the remains of
which are found in the rocks as fossils. Including all the forms of
life known to Palæontology, we should find that the dissimilarities
between the various groups would tend to disappear. The gaps between
existing Birds and Reptiles, for instance, would become partially
bridged. Palæontology would also supplement morphology in another way.
The study of the structure of animals leads us to describe them as
“higher” and “lower”--higher in the sense of a greater complexity of
structure. Thus the body of a Carnivore is more complex than that of
a Fish, inasmuch as it possesses the homologues of the truly piscine
gills, but it also possesses a four-chambered heart instead of a
two-chambered one; and it possesses the mammalian lungs, diaphragm, and
placenta, structures which are not present in the Fish. Now, so far as
its imperfect materials go, palæontology shows us that the higher forms
of life appeared on the earth at a later date than did the lower forms.
The remains of Mammals, for instance, are first found in rocks which
are younger than (that is, they are superposed upon) those rocks in
which Reptiles first appear; and so also Reptiles appear later in the
rock series than do Fishes. Palæontology thus adds to the logical order
suggested by morphology a _chronological_ order of this nature: higher,
or more complex forms of life appeared at a later date in the history
of the earth than did lower or less complex ones.
A parallel chronological sequence would also be suggested by the
results of embryology. This branch of biology shows us that
all animals pass through a series of stages in their individual
development, or ontogeny. The earlier stages represent a simple type of
structure, usually a hollow ball of cells, but as development proceeds,
the structure of the embryo becomes more and more complex. The process
of development is continuous in many animals, but in others (perhaps in
most) larval stages appear, that is, development is interrupted, and
the animal may lead for a time an independent existence similar to that
of the fully developed form. Often these larval stages suggest types
of structure lower than that of the fully developed animal into which
they transform. Even if larval stages may not appear in the ontogeny,
it is very often the case that the developing embryo exhibits traces,
or at least reminiscences, of the types of morphology characteristic
of the animals which are lower or less complex than itself; thus the
piscine gills appear during the development of the tailed Amphibian,
and even in that of the Mammal, and then vanish, or are converted into
organs of another kind. The individual thus passes through a series
of developmental stages of increasing complexity: it repeats, in its
ontogeny, the palæontological sequence in a distorted and abbreviated
form.
It is true that the evidence afforded by palæontology is very meagre.
The preservation of the remains of organisms in the stratified rocks is
a very haphazard process, and it depends for its success on a series
of conditions that are not always present. As the surface of the earth
becomes better known, our knowledge of the life of the past will become
fuller, but there can be little doubt that whole series of organisms
must have existed in the past, and that no recognisable traces of
these are known to us. There is also no doubt that the sequences
indicated by palæontology are very incomplete: they are obscured and
shortened by many conditions. The earlier embryologists entertained
hopes that the study of embryology would reveal the direction of the
evolutionary process in many groups of animals: if the organism repeats
in its ontogeny the series of stages through which it passed in its
phylogenetic development, then a close study of the embryological
process ought to disclose these stages. Although these hopes have
not been realised, there is yet sufficient truth in the doctrine of
recapitulation to enable us to state that there is a rough parallelism
between the palæontological and embryological sequences.
We therefore state a plausible hypothesis when we assert that
different species may be related to each other in the same way that
the individuals of the same species are related, that is, by a tie
of blood-relationship; and that different genera, families, orders,
and so on are also so related. Morphological studies enable us to
arrange numbers of species in such a way that series, in each of which
there is an increasing specialisation of structure, are formed. Both
palæontology and embryology show, to some extent at least, that these
stages of ever-increasing specialisation of structure occurred one
after the other. Now, stated briefly and baldly as we have put it, this
argument may not appear to the general reader to possess much force,
but it is almost impossible to over-state the strength of the appeal
which it makes to the student of biology. To such a one a belief in a
process of transformism will appear to be inseparable from a reasoned
description of the facts of the science.
But it would be no more than a belief, not even a hypothesis, if we
did not attempt to verify it experimentally. It is merely logical
relationships that we establish, and the chronological succession of
forms of life, higher forms succeeding lower ones, does not itself do
more than suggest an evolutionary process. All that we have said is
compatible with a belief in a process of special creation. But if we
cling to such a belief, if we suppose that the organisms inhabiting
the earth, now and in the past, are the manifestations of a Creative
Thought, we must still accept the notion of logical and chronological
relationships between all these forms of life. If we permit ourselves
to speculate on the working of the Creative Thought, we seem to
recognise that the ideas of the different species must have generated
each other, and that the genesis of living things must have occurred
in some such order as is indicated by a scientific hypothesis of
transformism. An evolutionary process must have occurred somewhere, but
the kinships so established between organisms would be logical and not
material ones.
Science must not, of course, describe the mode of origin of species
in this way. So long as it investigates living things by the same
methods which it uses in the investigation of inorganic things, it
must hold that the concepts of physical science are also adequate for
the description of organic nature. It must assume that matter and
energy and natural law are given; and that, even in the conditions of
our world, life must have originated from lifeless matter; must have
shaped itself, and undergone the transformations that are suggested
by the results of biology. It must assume, in spite of the formidable
difficulties that the assumption encounters, that cosmic physical
processes are reversible and cyclical; and that worlds and solar
systems are born, evolve, and decay again. Every stage in such a cosmic
process, as well as every stage in the evolution of living things,
must have been inevitably determined by the stages preceding it. Such
a mechanistic explanation must assume that a superhuman intellect,
but still a finite intellect like our own, such a calculator as that
imagined by Laplace or Du Bois-Reymond, would be able to deduce any
state of the world, or universal system, from any other state, by means
of an immense system of differential equations. It would be able, as
Huxley says, to calculate the fauna of Great Britain from a knowledge
of the properties of the primitive nebulosity with as much certainty
as we can say what will be the fate of a man’s breath on a frosty day.
Such a fine notion as that of an universal mathematics must ever remain
as the ideal towards which science strives to approximate.
Or we may suppose that a plan or design has been superposed on nature,
is immanent in matter and energy, and works itself out, so to speak.
Such a teleological explanation of inorganic and organic evolution
inevitably forces itself upon us if we reject the notion of radical
mechanism. We think of an universal system of matter and energies as
consisting of elements which, when assembled together, interact in a
certain way, and with results which are definite and calculable. The
assembling together of the elements of the system would be the result
of the previous phases of the system. That is radical mechanism.
But let us think of the elements of the system as being differently
assembled--thus involving the idea of an agency, external to the
system, which rearranges them--then the same energies inherent in
this system, as in that previously imagined, will also work out by
themselves. But the result will be different, and will depend on the
manner in which the elements were originally arranged. That would be
radical finalism.
Science must reject this notion as it rejects that of special creation,
since it introduces indeterminism into the evolutionary process. It
must regard the organism and its environment as a physico-chemical
system studied from without. It must avoid all attempts to acquire an
intuitive knowledge of the actions of the organism, for the latter, and
the things which environ it, are only bodies moving in nature. In the
systems studied by it time must be the independent variable, and there
must be a strict functionality between the parts of the organism and
the parts of the reacting environment, so that any change in the one
must necessarily be dependent on a change in the other. Such a system
and series of interactions is that which is described in a mechanistic
hypothesis of transformism.
All this is indeed suggested to ordinary and aided methods of
observation. The plant or animal acts upon, and is acted on by, the
environment, though it is usually the modification of the organism to
which we attend. A man’s face becomes reddened by wind and sun and
rain; manual labour roughens his hands and develops callosities; in the
summer he sweats and loses heat; in the winter the blood-vessels of his
skin contract and heat is economised. In the winter months the fur of
many animals becomes more luxuriant and may change in colour. Fishes
which inhabit lightly coloured sand are lightly pigmented, but their
skins become dark when they move on to darkly coloured sea-bottoms;
prawns which are brown when they live on brown weed, become green when
they are placed on green weed. Birds migrate into warmer countries,
and _vice versa_, when the seasons change. Such are instances of the
adaptations of the morphology and functioning of organisms consequent
on changes of environment.
What is an adaptation? The term plays a great part in biological
speculation, but it is often used in a loose and inaccurate manner,
and not always in the same sense. It suggests that the organism is
_contained_ by the environment, and that its form becomes adapted to
that of the latter, just as the metal which the ironfounder pours into
the mould takes the form of the cavity in the sand. “We see once more
how plastic is the organism in the grasp of its environment”--such
a quotation from morphological literature is perhaps a typical one.
Over and over again this passive change in the organism as the result
of the action of something rigid which presses upon it is what is
understood by an adaptation. No doubt the organism may be so affected,
and often the change which it experiences is of the same order as the
environmental change. In the winter many animals become sluggish and
may hibernate; their heart-beats slow down; their respiratory movements
become less frequent, and generally the rate of metabolism, that is
the rapidity with which chemical reactions proceed in their tissues,
becomes lessened. All these changes become reversed in sign when the
temperature again rises. The time of year at which a fish spawns
depends on the nature of the previous season. The rate of development
of the egg of a cold-blooded animal varies with the temperature.
The quantity of starch formed in a green leaf depends on certain
variables--the intensity of light, the temperature, and the quantity
of carbonic acid contained in the medium in which it is placed. In
all these cases the rate at which certain metabolic processes go on
in the body of an organism varies according to the conditions of the
environment. In general they are cases of van’t Hoff’s law, that is,
the rapidity at which a chemical reaction proceeds varies according to
the temperature.
They are changes of functioning passively experienced by the organism
as the result of environmental changes, and we must clearly distinguish
between them and such changes as are the result of some activity or
effort on the part of the organism. A flounder which lives in a river
migrates out to sea when the first of the winter snows melt and flood
the estuary with ice-cold water. Brown or striped prawns living on
brown or striped weeds become green when they are placed on green
weed, changing their pigmentation to match that of the alga. A kitten
brought up in a cold-storage warehouse develops a sleeker and more
luxuriant coat than does its sister reared in a well-warmed house. An
animal which recovers from diphtheria forms an antitoxin which enables
it to resist, for a time at least, repeated infection. A man who goes
exploring in polar seas puts on warmer clothing than he wears in the
tropics.
It is not necessary that an environmental change should occur in
order that an adaptation should be evoked, for the organism may react
actively and purposefully to a change in itself. The athlete acquires
by running or rowing a more powerful heart; the blacksmith develops
more muscular shoulders and arms; and the professional pianist more
supple wrists and fingers. If one kidney is removed by operation,
or if one lung becomes diseased, the organ on the other side of the
body becomes hypertrophied. Aphasia, which is due to a lesion in the
unilateral speech-centre, may pass away if the previously unused centre
on the other side of the brain should become functionally active. In
general, the continued use of an organ leads to its increase in size
and efficiency, and conversely disuse leads to a decrease of size and
even to atrophy.
The essence of an adaptation is that it is an active, purposeful change
of behaviour, or functioning, or morphology, by which the organism
_responds_ to some change in its physical environment, or to some
other change in its own behaviour, or functioning, or morphology.
It is also a change which remains as a permanent character in the
organisation of the animal exhibiting it. It does not matter even if
the change of behaviour is one which is willed in response to some
change of environment actually experienced, or whether it anticipates
some change that is foreseen. A changed mode of behaviour adapted
intelligently leaves, at the least, a memory which becomes a permanent
part of the consciousness of the animal, and may influence its future
actions; or if it is evoked by a process of education it must involve
the establishment of a “motor habit.” The education of a singer sets
up, in the cortex and lower centres of the brain, a nervous mechanism
which controls and co-ordinates the muscles of the chest and larynx,
and which did not exist prior to the process of education. Adaptations
are therefore acquired changes of some kind or other by means of which
the organism is able to exert a greater degree of mastery over its
environment, including in the latter both the inert matter of inorganic
nature and the other organisms with which the animal competes.
They are acquirements because of which the organism deviates from
the morphological structure characteristic of the species to which
it belongs. Do they affect the entire organisation of the animal
exhibiting them, that is, may an acquired change of structure be so
fundamental that it affects not only the body of the animal in which
it occurs but also the progeny of this animal? Let us suppose that
this is the case; let us suppose that quite a large proportion of
all the individuals of a species inhabiting a restricted part of the
earth’s surface acquire the same change of character simultaneously
and that they transmit this deviation of structure to their progeny.
Then we should have an adequate means whereby the specific type becomes
modified--a means of transformism.
This is the hypothesis which is associated with the name of Lamarck,
and its essential postulate is that characters which are acquired by
an organism during its own lifetime are transmitted to its offspring.
It seems reasonable to suppose that this transmission of acquired
characters should occur--how reasonable we should note when we see that
de Vries tacitly assumes that fluctuating variations due to the action
of the environment may be inherited by the offspring of organisms which
exhibit them. That transmutation of species might occur in this way was
a popular and widespread belief in England and Germany throughout the
greater part of the nineteenth century; and it was a belief entertained
by Darwin himself, and confidently, and even dogmatically affirmed at
one time by the majority of biologists in both countries.
How was it, then, that a very general change of opinion with regard
to this question occurred both in England and Germany during the
last two decades of the last century? Certainly many botanists and
zoologists continued to adhere to the older hypothesis, and most
physiologists still do not appear to make any clear distinction between
morphological characters which are inherited and those which are
acquired; but the majority of biologists did not hesitate to conclude
that not only was the transmission of acquired characters an unproved
conjecture, but that it was even theoretically inconceivable. At the
beginning of the nineteenth century this belief had almost become a
doctrine dogmatically asserted, and one cannot fail to notice a tone
of irritation and impatience on the part of the spokesmen of zoology
when the contrary opinions are expressed. “Nature,” says Sir E. Ray
Lankester, “(and there’s an end of it) does not use acquired characters
in the making and sustaining of species for the very simple reason that
she cannot do so.”
There can be little doubt that the interrogation of nature with regard
to this question was not a very thorough process. The dogmatic denial
of the transmission of acquired characters was not the result of
exhaustive experiment and observation, but was due rather to the very
general acceptance in England and Germany of Darwin’s hypothesis of
the transmutation of species by means of natural selection, and of
Weismann’s hypothesis of the continuity of the germ-plasm.
The newer hypothesis of transmutation was one which seemed adequate to
account for the diversity of forms of life, so that it was unnecessary
to invoke the older one; though Darwin himself admitted that the
individual acquirement of structural modifications might be a factor
in the evolutionary process; and for more than twenty years after the
publication of the “Origin of Species” Lamarck’s hypothesis was not
strenuously denied by naturalists. Early in the ’eighties, however,
Weismann published his book on the germ-plasm, and the brilliancy and
constructive ability of the speculations contained in this remarkable
work, as well as the analogies which they suggested between organic
and inorganic phenomena, compelled the attention of biologists. The
essential parts of Weismann’s hypothesis, as it was first presented to
the world, are as follows: very early in the evolution of living from
non-living matter many kinds of life-substance came into existence.
These were chemical compounds of great complexity, able to accumulate
and expend energy, and capable of indefinite growth and reproduction.
They were able to exist in an environment which was hostile to them and
which tended always to their dissolution, and which was able to modify
their nature and their manner of reacting, though it could not destroy
them. These elementary life-substances were very different from those
which we know in the world of to-day. They were _naked_ protoplasmic
aggregates, undifferentiated into cellular or nuclear plasmata, much
less into somatic and germinal tissues. All of their parts were
similar, or rather their substance was homogeneous. But even with the
evolution of the unicellular organism a profound change was initiated,
for henceforth one part of the living entity, the nucleus, became
charged with the function of reproduction, although it still continued
to exercise general control over the functions of the extra-nuclear
part of the cell. When the multi-cellular plant and animal became
evolved, the heterogeneity of the parts of the organism became greater
still. All the cells of the metazoan animal do indeed contain nuclei,
but these structures are only the functional centres of the cells: some
of the latter are sensory, others motor, others assimilatory, others
excretory, and so on. Only in the nuclei which form the essential parts
of the reproductive organs does the reproductive function persist in
all its entire potentiality: there only does the protoplasm retain all
the properties which were possessed by the primitive life-substance
before it became heterogeneous, that is, before nucleus and cytoplasm
evolved. When part of the primitive life-substance became secluded in a
nuclear envelope, it became, to that extent, shielded from the action
of the physical environment, and when the organism became composed of
multicellular tissues this seclusion became more complete. Clothed
in the garments of the flesh, it was henceforth protected from the
shocks of the environment, and it became the immutable germ-plasm.
But for a very long time before this evolution of tissues the naked
life-substance had been exposed to the action of external physical
agencies, and it had been modified by these into very numerous
forms of protoplasmic matter. When multicellular plants and animals
had been evolved there were, therefore, not one, but many kinds of
life-substance in existence, and these have persisted until to-day as
the unchanging germ-plasmata of the existing organisms.
The Weismannian hypothesis of to-day, supported and amplified, as it
is, by subsidiary hypotheses, does not make the same appeal to the
student as did the pristine and altogether attractive speculation
of thirty years ago. The analogy which it then presented with the
matured chemical theory of matter must have been almost irresistible.
Just as the indefinitely numerous compounds of chemistry are only the
permutations and combinations of some of eighty-odd different kinds
of matter, so all the forms of life are combinations and permutations
of some of the many different kinds of life-substance which came into
existence before the evolution of the multicellular organism. And just
as the chemical elements were regarded (in 1883) as immutable things,
preserving their individuality even when they were associated together
as compounds, so Weismann and his followers looked upon the different
kinds of life-substance contained in the chromatic matter of the
nucleus as immutable and immortal living entities. Associated together
in indefinitely numerous ways by sexual conjugation, they may build up
indefinitely variable living structures, but they remain individualised
and lying side by side in the germ-plasmata of organisms, just as the
atoms were supposed to lie side by side in the chemical molecule of the
inorganic compound.[31]
[31] We know now that this statement is not quite accurate.
If these speculations were true, a change of morphology or functioning,
acquired by the body, or somatoplasm, could not possibly be transmitted
to the progeny of the organism, for by hypothesis the germ-plasm
cannot be affected by external changes, and it is only the germ-plasm
contained in the spermatozoon of the male parent, or in the ovum of
the female, that shapes and builds the body of the offspring. As if
this were not enough, Weismann and his followers argued that the
transmissibility of a somatic change to the germ was inconceivable.
Why? Because the germ-cells are apparently simple: they are only
semi-fluid protoplasmic cell bodies and nuclei, not differing
appreciably from the cell bodies and nuclei of the somatoplasm (by
hypothesis, it should be noted, the difference is profound). There are
no structural connections--no nerves, for instance--which join together
the cells of the bodily tissues with the parts of the germ and transmit
changes in the former to the latter. How, then, could a somatic change
affect the germ so that when the latter developed into an organism
this particular change became reproduced? Now this may have seemed a
conclusive argument in 1883, but is it so conclusive to-day? We know
that the cells and tissues are not isolated particles, but that all are
connected together by protoplasmic filaments. We know that specialised
nervous tissues are not necessary for the transmission of an impulse
from a sensory to a motor surface, but that such an impulse may be
transmitted by undifferentiated protoplasm. We know that nerve-cells
and nerve-fibres are not structurally continuous with each other but
that the impulse leaps across gaps, so to speak. We know that events
that occur in one part of the body of the mammal may affect other parts
by means of the liberation of a chemical substance, or hormone, into
the blood stream. It would be strange indeed if a logical hypothesis
capable of accounting for the transmission of a particular change from
the soma to the germ could not be elaborated.
But acquired characters were not really transmitted after all. So
those who clung to Weismannism argued--an unnecessary task surely
if this transmissibility were inconceivable. We cannot discuss the
evidence here, and it is unnecessary that we should do so, since it is
all considered in the popular books on heredity. There is an apparent
consensus of opinion in these books which should not influence the
reader unfamiliar with zoological literature, nor obscure the fact
that many zoologists and botanists accept the opposite conclusion.
The discussion is all very tiresome, but we may glean some results of
positive value from it. It is unquestionable that very few conclusive
and adequate investigations have been made: one cannot help noticing
that the literature contains an amount of controversy out of all
proportion to the amount of sound experimental and observational
work actually carried out. Most of the experiments deal with the
consideration of traumatic lesions or mutilations, and it seems to be
proved that such defects are not transmitted, or at least are very
rarely transmitted. The tails of kittens have been cut off; the ears
of terrier-dogs have been lopped; and the feet and waists of Chinese
and European ladies have been compressed, and all throughout very
numerous generations, yet these defects are not transmitted from parent
to offspring. This kind of evidence forms the bulk of that which
orthodox zoological opinion has adduced in favour of the belief in
the non-inheritability of acquired characters, but does it all really
matter? What might be transmitted is a useful, purposeful modification
of morphology, or functioning, or behaviour, induced by the environment
throughout a number of generations--an adaptation rather than a harmful
lesion. There is little conclusive evidence that such adaptations
are inherited, though anyone who carefully studies the evidence in
existence will not be likely to say that they are certainly not
transmitted. Does, for instance, the blacksmith transmit his muscular
shoulders and arms to his sons, or the pianiste her supple wrists and
fingers to her daughters? There are no observations and experiments in
the literature worthy of the importance attaching to the question at
issue.
It should be noted also that the germ-plasm is certainly not the
immutable substance that the hypothesis originally postulated. Changes
in the outer physical environment may certainly affect it; thus the
larvæ bred from animals which live in abnormal physical conditions
(temperature, moisture, etc.) may differ morphologically from the larvæ
bred from animals belonging to the same species but living in a normal
environment. The latter must therefore react on the germ-plasm, but the
environment formed by the bodily tissues which surround the germ-cells
may also so react: thus the germ-cells may be affected by such bodily
changes as differences in the supply of nutritive matter, for instance.
The offspring may deviate from the parental structure as the result
of structural modifications acquired by the parent during its own
lifetime, and, even if the filial deviation were not of the same nature
as the parental modification, its inheritance would be an adequate
cause of _some_ degree of transmutation.
It is, however, certainly difficult to prove that organisms transmit
to their progeny the _same_ kinds of deviation from the specific
structure that they themselves acquire as the result of the action of
the environment. Even if they did transmit such acquired deviations,
it does not seem clear that this kind of inheritance alone would
be a sufficient cause of the diversity of forms of life that we do
actually observe in nature. Change of morphology would indeed occur,
but we should expect to find insensible gradations of form and not
individualised species. Let us suppose that Lamarckian inheritance
acts for a considerable time on two or three originally distinct
species inhabiting an isolated tract of land, and let us suppose that
we investigate the variations occurring among all the organisms which
are accessible to our observation with respect to some one variable
character.
The diagram _A_ represents what would seem to be the result of this
process of transmutation. The numbers along the horizontal line are
proportional to their distance from o, the origin, and represent the
magnitude of the variation considered; and the height of the vertical
lines represents the number of organisms exhibiting each degree of
variation. We should expect to find that all the variations were
equally frequent in their occurrence, but this is not what a study of
variability in such a case as we have supposed--that of the animals
inhabiting an isolated part of land--does actually indicate. What we
should find would be the conditions represented by the diagram _B_.
There would be two or more _modes_, that is, values of the variable
character which are represented by a greater number of individuals than
any other value of the variation. The environmental conditions _favour_
the individuals displaying this variation to a greater extent than they
favour the rest.
[Illustration: FIG. 24.]
That is to say, the environment selects some kinds of variations among
the many that are exhibited, and this is, of course, the essential
feature of the hypothesis of the transmutation of species by means of
natural selection of variable characters. Organisms enter the world
differently endowed with the power of acting on the medium in which
they live, or on the environment consisting of their fellow-organisms.
Those that are most favourably endowed live longest and have a more
numerous progeny than those that are less favourably endowed, and
they transmit this favourable endowment to their offspring. Among
the progeny of the progeny there may be some in which the favourable
variation is still more favourable than it was when it first appeared.
Thus the variations which are selected increase in amount. Elimination
of the weakest occurs. The idea is eminently clear and simple, and
possesses a great degree of generality: it is self-evident, says
Driesch, meaning that it cannot be refuted, for it was certainly not
clearly obvious to the naturalists before Darwin and Wallace. But,
unless we choose to be dogmatic, we can hardly claim that it is an
all-sufficient cause for the evolutionary process, and it is useless
to attempt to minimise the difficulties of the hypothesis. It is not
easy to make it account for the origin of instincts or tropisms, or for
restitutions and regenerations of lost parts, or for the appearance
of the first non-functional rudiments of organs which later become
functional and useful. It is, indeed, possible to devise plausible
hypotheses accounting for all these things in terms of natural
selection, but each such subsidiary hypothesis loads the original one
and weakens it to that extent.
Natural selection does not, of course, induce or evoke variations;
these are given to its activity, and they are the material on which it
operates. What, then, is the nature of the deviations from the specific
types of morphology that are selected or eliminated? Not those induced
by the environment, and transmitted in their nature and direction to
the progeny of the organisms first displaying them. It is not unproved
that such variations do occur, and it is even probable that they do
occur. But we may conclude that the frequency of their occurrence is
not great enough to afford sufficient material for natural selection.
It is also clear that the ordinarily occurring variations that we
observe in any large group of organisms collected at random are not
alone the material for selection; for we have seen that experimental
breeding from such variations does not lead to the establishment of a
stable race or “variety.” Nevertheless some effect is produced, and
this may be accounted for by supposing that the observed variations are
really of two kinds--fluctuating variations, which are not inherited,
and mutations, which are inherited. The small observed effect is due to
the selection of the mutations alone: it is a real effect of selection,
an undoubted transmutation of the specific form, but experimental
and statistical investigations seem to show that selection from the
variations that we usually observe is too slow a process to account for
the existing forms of life.
Natural selection acts, therefore, on mutations. Now it seems that we
are forced to recognise the existence of two categories of mutations,
(1) those stable modifications of an “unit-character” which we term
“Mendelian characters,” and (2) those groups of stable modifications to
which de Vries applied the term mutations. It seems at first difficult
to see how permanent modifications of the specific form can be brought
about by the transmission of Mendelian characters, for these characters
are always transmitted in pairs. Let us take a concrete case--that of
a man who has six fingers on his right hand, and let us suppose that
this was a real, spontaneously appearing character or mutation which
had not previously occurred in the ancestry of the man. Two contrasting
characters would then be transmitted, (1) the normal five-fingered
hand, and (2) the six-fingered hand. Both of these characters are
supposed to be present at the same time in the organisation of the men
and women of the family originating in this individual, but one of them
is always latent or recessive. There would, however, be individuals in
which only one of the characters would be present--either the normal
or abnormal number of digits, but intermarriage with individuals
belonging to the other pure strain would immediately lead again to
the transmission of the contrasting characters, or allelomorphs,
although marriage with an individual belonging to the same pure strain
would carry on the normal or abnormal unmixed character into another
generation. But if the possession of six fingers conveyed an undoubted
advantage, and if natural selection did really act in civilised man as
regards the transmission of morphological characters, then a stable
variety (_Homo sapiens hexadactylus_, let us say) might be produced
by its agency. The mutations which we consider in the investigation
of the inheritance of alternating characters are therefore just as
much the material for natural selections as the mutations which occur
among the ordinary variations displayed by organisms in general: but
since only one or two characters appear to be subject to this mode of
transmission, the process would be so slow as to be inadmissible as an
exclusive cause of evolution.
If we assume that de Vries’ mutations are the material on which
selection works, this difficulty is immediately removed, for we now
have to deal with _groups_ of stable deviations: not one or two, but
_all_ the characters of the organism appear to share in the mutability.
But another difficulty now arises. A species of plant or animal may
have got along very well with its ordinary structural endowment, and
then a number of individuals begin to mutate. Some of the deviations
from the specific type may be of real advantage, but others may not:
we can, indeed, imagine an in-co-ordination between the mutating parts
or organs which would be fatal to the animal; on the other hand,
there might be complete co-ordination, with the result that great
advantage might be conferred upon the individual. It is easy to see
how co-ordination of mutating parts is absolutely essential. An animal
which preserves its existence by successful avoidance of its enemies
would not be greatly benefited by a more transparent crystalline lens
if the vitreous humour of its eye were slightly opaque; and even if all
the parts of the eye were perfectly co-ordinated, increased acuity of
vision would not greatly help it if its limbs were not able to respond
all the more quickly to the more acute sensation. Un-co-ordinated
mutations would therefore tend to become eliminated, while co-ordinated
ones would become selected and would become the characters of new
species.
We must now ask why some groups of variations are co-ordinated while
others are not, and it is here that we encounter the most formidable of
the difficulties of any hypothesis of transformism which depends on the
concept of natural selection. If we assume that the environment induces
the appearance of variations, it seems to follow that these variations
are likely to be co-ordinated, but we then invoke the principle of the
acquirement of characters and their transmission by heredity. If, on
the other hand, we assume that variations appear spontaneously, and
quite irresponsibly, so to speak, in the germ-plasm of the organism,
the selection, or elimination, by the environment will not occur until
the co-ordinated or un-co-ordinated variations appear. It is far more
likely that a large number of simultaneously appearing variations will
be un-co-ordinated than that they will be co-ordinated. Merely as a
matter of probability the progressive modification of a species will
take place slowly--too slowly to account for what we see.
Two examples will make it easier to appreciate this difficulty.
Evolution has undoubtedly proceeded in definite _directions_.
There are two dominant groups of fishes, the Teleosts and the
Elasmobranchs, and both must have originated from a common stock.
All the characters in each kind of fish must have been useful (since
they were selected), and all must have been modifications of the
characters of the common stock. The latter became modified along two
main lines, or directions, which are indicated by the characters of the
existing Teleosts and Elasmobranchs. The whole skeleton, the gills,
the circulatory system, and the brain differ in certain respects in
these groups. Therefore a modification of the brain in the primitive
Elasmobranchs was associated with a modification of the cranium, and
therefore with the jaw-apparatus, and so with the branchial skeleton
and the gills, and therefore also with the heart, and so on. Suppose
that the evolutionary process included ten useful and co-ordinated
variations--not an unlikely hypothesis--and suppose that each of these
ten useful variations was associated with nineteen useless ones. The
chance that any one of them did occur was therefore one in twenty; and
if they all occurred independently, that is, if the occurrence of any
one of them was compatible with the occurrence of any other one, or of
all the others, then the chance that all the ten variations occurred
simultaneously was 20^{-10} that is, one in the number 20 followed by
10 cyphers, a rather great improbability.
Most biological students are familiar with the similarity of the
so-called eye of the mollusc Pecten and that of the vertebrate. The
resemblance is one of general structure: in each of these organs
there is a _camera obscura_, a transparent cornea, and behind that
a crystalline lens. On the posterior wall of the camera there is a
receptor organ, or retina, and this is composed of several layers of
nervous elements. The actual nerve-endings are on the surface of
the retina, which is turned away from the light, that is, the optic
nerve runs towards the anterior surface of the retina, and then its
fibres turn backwards. This “inversion of the retinal layers” occurs
in all vertebrate animals, but it is exceptional in the invertebrates.
The above general description applies equally well to the eye of the
vertebrate and to that of Pecten.
Let us admit that these mantle organs in Pecten _are_ eyes, for
there is no conclusive experimental evidence that they really are
visual organs, and plausible reasoning suggests that they may
subserve other functions. Let us assume that the minute structure of
the Pecten eye is similar to that of the vertebrate, and that its
development is also similar: as a matter of fact both histology and
embryology are different. Then we have to explain, on the principles
of natural selection, the parallel evolution of similar structures
along independent lines of descent; for mollusc and vertebrate have
certainly been evolved from some very remote common ancestor in which
the eye could not have been more than a simple pigment spot with a
special nerve termination behind it. In each case the organ was formed
by a very great number of serially occurring variations, yet these
two sets of variations must have been the same at each stage in two
independently occurring processes. On any reasonable assumption as to
the number of co-ordinated variations required, and their chances of
occurrence, the mathematical improbability that these two series of
variations did occur is so great as to amount to impossibility so far
as our theory of transformism is concerned. Natural selection could
not, therefore, have produced these two organs.
This argument of Bergson’s fails, of course, in the particular
instance chosen by him, but this is because the case is an unfortunate
one. Probably a morphologist could find a very much better case of
convergent evolution--the parallelism between the teeth of some
Marsupials and some Rodents, for instance. If detailed histological and
embryological investigation should show a similarity of structure and
development, in such compared organs Bergson’s argument would retain
all its force. We should then have to assume that there was a directing
agency, or tendency in the organism, co-ordinating, or perhaps actually
producing, variations.
Mechanistic biology can suggest no means whereby simultaneously
occurring variations are co-ordinated: let us therefore think of
these variations as occurring independently of each other, and let us
ignore the difficulty of the infrequency of occurrence of suitably
co-ordinated variations. Variations _are_ exhibited by the evolving
organism, and the selection of co-ordinated series is the work of the
environment. But the environment is merely a passive agency, and it
has to confer direction on the innumerable variations presented to it
by the organism, rejecting most but selecting some. Let us think of
the environment, says a critic of Bergson, as a blank wall against
which numerous jets of sand are being projected. The jets scatter
as they approach the wall: each of them represents the variations
displayed by some organ or organ-system of an animal. Let us think of
a pattern drawn on the wall in some kind of adhesive substance: where
the wall is blank the sand would strike, but would fall off again, but
it would adhere to the parts covered by the adhesive paint. The sand
grains strike the wall from all sides, that is, their directions are
un-co-ordinated. The wall is passive, yet a pattern is imprinted upon
it. From passivity and un-co-ordination come symmetry and order.
This argument withstands superficial examination, but to accept it
is truly to be “fooled by a metaphor.” _For what is the pattern on
the wall?_ It is the environment, says the critic. But what is the
environment? Inevitably we think of it as something that makes or
moulds the organism, a way of regarding it that drags after it all
the confusion of thought implied in the above analogy. Clearly the
environment is made by the organism. Its _form_, that is, space,
is only the mode of motion possible to the organism; it is clear
that whether the space perceived by an organism is one-, two-, or
three-dimensional, space depends upon its mode of motion. Its universe
is whatever it can act upon, actually or in contemplation. Atoms and
molecules, planets and suns are its environment because it can in some
measure act upon these bodies, or at least they can be made useful to
it. Chloroform or saccharine, or methyl-blue and all the dye-stuffs
prepared from coal-tar by the chemists, are part of our environment
because we have _made them_. They existed only in potentiality prior to
the development of organic chemistry. They were possible, but man had
to assemble their elements before they became actual. In _making_ them,
he conferred _direction_ on inorganic reactions.
Surely the organism itself selects the variations of structure and
functioning that are exhibited by itself. If we hesitate to say
that these modifications are creations, let us say that they are
permutations of elements of structure, and that they were potential
in the organisation of the creature exhibiting them. They occur in
the latter if we must not say that they are produced. If they are
detrimental, the organism is the less able to live and reproduce, and
if it does reproduce, its progeny are subject to the same disability.
If, as is usual, they simply do not matter, they may or may not affect
the direction of evolution. If they are of advantage, that is, if they
confer increased mastery over the environment, over the inert things
with which the organism comes into contact, the latter enlarges its
universe or environment, lives longer, and transmits to its progeny its
increased powers of action. Indefinite increase of power over inert
matter is potential in living things, and variation converts this
potentiality into actuality.
This discussion is all very formal, but two conclusions emerge from it:
(1) the insufficiency of the mechanistic hypotheses of transformism
to account for all the diversity of life that has appeared on the
earth during the limited period of time which physics allows for the
evolutionary process. There does not appear to be any possibility of
meeting this objection if we continue to adhere to the hypothesis
of transformism already discussed: it faces us at every turn in our
discussion. How great a part is played, for instance, by “pure chance”
in the elimination of individual organisms during the struggle for
existence! Let us think of a shoal of sprats on which sea-birds are
feeding: it is chance which determines whether the birds prey on one
part of the shoal rather than another. Or let us think of the millions
of young fishes that are left stranded on the sea-shore by the receding
tide: it is chance that determines whether an individual fish will be
left stranded in a shallow sandpool which dries up under the sun’s
rays, rather than in a deeper one that retains its water until the tide
next flows over it. It is no use to urge that there is no such thing
as “pure chance,” and that what we so speak of is only the summation
of a multitude of small independent causes. Let us grant this, and
it still follows that the alternative of life or death to multitudes
of organisms depends not upon their adaptability but upon minute
un-co-ordinated causes which have nothing to do with their morphology
or behaviour. These are instances among many others which will occur
to the field naturalist: they shorten still further the time available
for natural selection in the shaping of species, for they reduce the
material on which this factor operates.
The other result of our discussion is to indicate that the problem
of transformism of species is in reality the problem of organic
variability. Let us assume that all the hypotheses of evolution
are true: that the environment may induce changes of morphology
and functioning in animals and plants, and that these changes
themselves--the actual acquirements themselves, that is--are
transmissible by heredity. Let us assume that the germ-cells may be
affected by the environment, either the outer physical environment, or
the inner somatic environment, and that mutations may thus arise. Let
us assume that mutations may be selected in some way, so that specific
discontinuities of structure--“individualised” categories of organisms,
or species--may thus come into existence. Even then transformism is
still as great a problem as ever, for the question of the mode of
origin of these variations or modifications still presses for solution.
The simplest possible cases that we can think of present the most
formidable difficulties. The muscles of the shoulders and arms of the
blacksmith become bigger and stronger as the result of his activity.
Why? We say that the increased katabolism of the tissues causes a
greater output of carbonic acid and other excretory substances, and
that these stimulate certain cerebral centres, which in turn accelerate
the rate of action of the heart and respiratory organs. An increased
flow of nutritive matter and oxygen then traverses the blood-vessels in
the muscles of the shoulders and arms, and the latter _grow_. Probably
processes of this kind do occur, but to say that they do is not to give
any real explanation of the hypertrophy of the musculature of the man’s
body, for what essentially occurs is the division of the nuclei and the
formation of new muscle fibres. How precisely does an increased supply
of nutritive matter cause these nuclei to divide and grow? This is a
relatively simple example of the adaptability of a single tissue-system
to a change in the general bodily activity, that is to say it is a
variation of structure induced by an environmental change.
In most cases, however, the variations of structure that form the
starting-points of transmutation processes cannot clearly be related to
environmental changes. Some fishes produce very great numbers of ova in
single broods--a female ling, for instance, is said to spawn annually
some eighteen millions of eggs. If we examine these ova we shall find
that there is considerable variation in the diameter and in other
measureable characters. We may attempt to correlate these deviations
from the mean characters with environmental differences. All the eggs
“mature,” that is, they absorb water and swell, while various parts,
such as the yolk, undergo chemical changes, during the month or so
before the fish spawns. This process of maturation takes place in the
closed ovarian sac; and the eggs lie practically free in this sac, and
are bathed in a fluid which exudes from the blood-vessels in its walls.
It may indeed be the case that there are variations in the composition
of this fluid in the different parts of the sac; but these variations
cannot be great; the fluid is not really a nutritive one; and the
process of maturation is not hurried. We can hardly believe that
the differences in morphology are due to these minute environmental
differences. We may indeed say that we do not really study the germ
cells when we measure the diameter of the egg or investigate any other
measurable character, for the real germ-plasm is the chromatic matter
of the nucleus. But this obviously begs the whole question: all the
parts of the egg that are accessible to observation do vary, and ought
we to conclude that the parts which are not accessible do not vary?
They _must_ vary: the germ-plasm of each egg _must_ be different from
that of all the others, for the organisms which develop from these
germs show inheritable differences. Further, can we contend that such
minute environmental differences as we have indicated affect the
germ-plasm? Is it so susceptible to external changes? A high degree of
stability of the germ-plasm is postulated in the mechanistic hypothesis
that we have considered, and indeed everything indicates that the
specific organisation is very stable. Can it then be upset by such
minute differences in the somatic environment?
But the germ-plasm is not really simple, says Weismann; it is a
complex mixture of ancestral germ-plasms. The individual fish that we
were considering arose from an aggregate of determinants, and half of
these determinants were received from the male parent and half from
the female one. But each of these parents also arose from a similar
aggregate of determinants, which again were received from both parents,
and so on throughout the ancestry of the fish. It is true that the
germ-plasms contributed by the ancestors were not quite different,
but they differed to some extent. Then there must have been as many
permutations of determinants in the ovum from which the fish developed
as there were permutations of characters in the eighteen millions of
ova produced by it. Does not the hypothesis collapse by its own weight?
It could only have been such difficulties as are here suggested that
led Weismann to formulate his hypothesis of germinal selection. All
those eighteen millions of eggs arose from the division of relatively
few germ cells. Each of these original cells contained the specific
assemblage of determinants, and the elements of the latter are of
course the biophors. The biophors, it will be remembered, are either
very complex chemical molecules, or aggregates of such. When the germ
cells of the germinal epithelium divide to form those cells which are
going to become the ova, the biophors must divide and grow to their
former size, and again divide--it is really a chemical hypothesis that
we are stating, though we have to employ language which seems to do
violence to all sound chemical notions! Now while the biophors were
dividing and growing they were “competing” for the food matter which
was in the liquid bathing them, and some got less, while others got
more than the average quantity. In this way their characters became
different, so that the eggs, on the attainment of maturity, became
different from each other. Now, apart altogether from the impossibility
of applying any test as to the objective reality of this hypothesis, it
must be rejected, for it confers on bodies which belong to the order of
molecules properties which are really those of aggregates of molecules.
The typical properties of a gas, for instance, are not the properties
of the molecules of which the gas is composed, but are statistical
properties exhibited by aggregates of molecules. On the hypothesis of
germinal selection the properties of the animals which develop from
the biophors are extended to the biophors themselves. It was surely a
desperate plight which evoked this notion! It is, as William James said
about Mr Bradley’s intellectualism, mechanism _in extremis_!
We seem forced to the conclusion--and this is the result to which all
this discussion is intended to approximate--that variations, heritable
variations at least, arise spontaneously. That is, there are organic
differences which have no causes, a conclusion against which all our
habits of reasoning rebel. Yet it may be possible to argue that the
problem of the causes of variations is really a pseudo-problem after
all, and that there is no logical reason why we should be compelled to
postulate such causes. When we think of organic variability, do we not
think, surreptitiously it may be, of something that varies, that is,
something that ought to be immutable but which is compelled to deviate?
But what is given to our observation is simply the variations among
organisms.
Let us think of the crude minting machines of Tudor times which
produced coins which were not very similar in weight and design. From
that time onward minting machines have continually been improved,
each successive engine turning out coins more and more alike in every
respect, so that we now possess machines which stamp out sovereigns
as nearly as possible identical with each other. Yet they are not
quite alike, and this is because the action of the engine, in all its
operations, is not invariably the same. In imagination, however, we
make a minting machine which does work perfectly, and turns out coins
absolutely alike, but this ideal engine is only the conceptual limit
to a series of machines each of which is more nearly perfect than was
the last one. It is unlikely that matter possesses the rigidity and
homogeneity which would enable us to obtain this perfect identity of
result; nevertheless this identity has a very obvious utility, and we
strive after it, so that the result of our activity is the conception
of a perfect mechanism, and of products which are identical. We assume
that the reasons why our early and cruder machines were imperfect are
also the reasons why our later and more perfect ones do not produce the
results that we desire.
We are artisans first of all, and then philosophers, and so we extend
this ingrained mechanism of the intellect into our speculations. To
the biologist the organism is a mechanism which, in reproduction,
_ought_ to turn out perfect replicas of itself. It does not do so.
Now, if biology shows us anything, it shows us that living matter is
essentially “labile,” that is, something fluent, while lifeless matter
is essentially rigid, or nearly so. Yet, ignoring this difference, we
expect from the organism that identity of result and operation that we
conceptualise, but do not actually obtain from the artificial machine.
We regard the organism, not only as a mechanism like the minting
machine, but as the conceptual limit to a series of mechanisms. The
reproductive apparatus of our fish does not turn out ova which are
identical, but which differ from each other. Some of this variation, we
say, is due to the action of the environment; and some of it is due to
the condition that each ovum receives a slightly different legacy of
characters from the multitude of ancestors. The rest we conceive as due
to the imperfect working of the reproductive machinery.
It is useful that science should so regard the working of the organism,
for in the search for the causes of variation our analysis of the
phenomena of life becomes more penetrating. But does any result of
investigation or reasoning justify us in assuming, as a matter of
pure speculation, that deviations from the specific type of structure
are physically determined in all their extent? Have we not just as
much justification for the belief that these deviations are truly
spontaneous, and that they arise _de novo_? So we approach, from the
point of view of experimental biology, Bergson’s idea of Creative
Evolution.
CHAPTER VII
THE MEANING OF EVOLUTION
Apart from experimental investigation, the results of comparative
anatomy, even if they are amplified by those of comparative embryology,
and even if they include fossil as well as living organisms, do no more
than suggest the occurrence of an evolutionary process. It is in vain
that we attempt a demonstration of transmutation of forms of life by
showing that a similarity of structure is to be observed in all animals
belonging to the same group. We may show successfully that the skeleton
of the limbs and limb-girdles of vertebrate animals is anatomically
the same series of parts, whether it be the arms and legs of man,
or the wings and legs of birds, or the pectoral and pelvic fins of
fishes: such homologies as these were indeed suggested by the mediæval
comparative anatomists apart altogether from any notions as to an
evolutionary process. We may show that the simplicity of the skeleton
of the head of man is apparent only, and that in it are to be traced
most of the anatomical elements that enter into the skull and visceral
arches of the fish; and that fusions and losses and translocations
of parts have occurred and can be made to account for the observed
differences of form. All this might just as easily be explained by
assuming a process of special creation, or the gradual development of a
plan or design. Just as God made Eve from a superfluous rib taken from
the body of her husband, so He may have formed the auditory ossicles of
the higher vertebrate from those parts of the visceral arches of the
lower forms which had become superfluous in the construction of the
more highly organised creature. However much the language of evolution
may force itself on biology, it does no more than symbolise the results
of anatomy and embryology, and provide a convenient framework on which
these may be arranged.
But if, as all modern experimental work shows, the form of the
organism is, in the long run, the result of its interaction with the
environment; if, as indeed we see, this form is not an immutable one,
but a stage in a flux; and if deviations from it may occur with all
the appearance of spontaneity, then it would appear that the observed
facts of comparative anatomy and embryology are capable of only one
explanation. They represent the results of an evolutionary process, and
the relationships that morphological studies indicate are no longer
merely logical, but really material ones. We can now endeavour to
utilise these results in the attempt to trace the directions taken by
the process of evolution.
In so doing we set up the schemes of phylogeny. We divide all organisms
into plants and animals, and then we subdivide each of these kingdoms
of life into a small number of sub-kingdoms, in each of which we set up
classes, orders, families, genera, and species. But our classification
is no longer merely a formal arrangement whereby we introduce order
into the confusion of naturally occurring things. It is now a “family
tree,” and from it we attempt to deduce the descent of any one of the
members represented in it.
The sub-kingdoms, or phyla, of organisms are the primary groups in this
evolutionary classification. We divide all animals into about nine of
these phyla--the Protozoa or unicellular organisms; the Porifera or
sponges; the Cœlenterates, a group which includes all such organisms as
Zoophytes, Corals, Sea-Anemones, and “Jelly-fishes”; the Platyhelminth
worms, that is the Tapeworms, Trematodes, and some other structurally
similar animals which live freely in nature; the Annelids, a rather
heterogeneous assemblage of creatures which includes all those animals
commonly called worms; the Echinoderms, which are the Star-fishes,
Sea-Urchins, and Feather-Stars found in the sea; the Molluscs, that
is the animals of which the Oyster, the Periwinkle, the Garden-Slug
and the Octopus are good examples; the Arthropods, which include the
Crustacea, the Insects, and the Spiders; and lastly the Vertebrates.
Any such classification we naturally endeavour to make as complete a
one as possible, but round the bases of the larger groups there cling
small groups of organisms the precise relationships of which are
doubtful. Yet, on the whole, these sub-kingdoms of organisms represent
clearly the main directions along which the present complexity of
animal structure has been evolved.
There is an essential structure which we endeavour to assign to all
the animals of each phylum, and which is different from the structure
of the animals belonging to all other phyla. The Protozoa, which for
the present we regard as animals, are organisms the bodies of which
consist of single cells. These cells may become aggregated into
colonies, but they may as well exist apart from each other. They may
be enclosed in limy, siliceous, or cellulose skeletons or shells, or
they may possess limy or siliceous spicules in their tissues--these
parts are non-essential, and the schematic Protozoan is a cell
containing a single nucleus, and capable of independent existence.
The Porifera, and all the other phyla, include organisms the bodies of
which are made up of aggregates of cells. In the Porifera the cells,
which are specially modified in structure, are arranged to form the
internal walls of a “sponge-work” the cavities of which open to the
outside by series of pores through which water is circulated. The
bodies of the Cœlenterates are typically sacs formed by a double wall
of cells--endoderm and ectoderm. This sac opens to the exterior by a
single opening, or mouth, surrounded by a circlet of tentacles, and
its cavity is the only one contained in the body of the animal. The
Platyhelminth worms are animals the bodies of which are also composed
of ectodermal and endodermal tissues, between which is intercalated
another mesodermal tissue. They have a single digestive sac or
alimentary canal opening to the exterior by means of a mouth only; and
they all possess a complex, hermaphrodite, reproductive apparatus. In
all the other phyla there are also three principal layers or kinds of
tissue, but in addition to the cavity of the alimentary canal there
is also a body cavity, or cœlom, which is contained in the mesodermal
tissues. The Echinoderms are such cœlomate animals, but the alimentary
canal now opens to the exterior by means of both mouth and anus;
there are separate systems of vessels through which water and blood
circulate; the blood-vascular system of vessels is closed to the
exterior, the water-vascular system being open; and the integument is
armed by means of calcareous spines or plates. The Annelids are animals
with cylindrically shaped bodies, segmented so as to form numerous
joints. Each segment bears spines or hairs or appendages of some sort,
and also contains a separate nerve-centre. The alimentary canal opens
externally by a mouth and anus, and there is a spacious body cavity.
The Molluscs are unsegmented animals. The dorsal part of their bodies
contains the viscera, and is protected by a shell; while the ventral
part is modified for the purpose of locomotion. A fold of integument
hangs down all round the body and encloses a cavity in which the gills
are contained. The Arthropods are segmented animals. The body is armed
by a calcareous carapace or shell which forms the exo-skeleton. Each
bodily segment bears a pair of jointed appendages, and also contains
a separate nerve-centre. The whole series of ganglia are connected
together by means of a nerve-cord, and the nervous system lies ventral
to the alimentary canal. The Vertebrata are also segmented animals,
but the segmentation is not apparent externally. The skeleton is an
internal one, and is built up round an axial rod or notochord. The
nervous system is situated dorsally to the alimentary canal. There are
two pairs of limbs.
Thus we set up an essential or schematic structure characteristic
of each phylum. These schemata have no real existence: they are
morphological types from which the actual bodily structure of the
animals in each phylum may be deduced. They represent the minimum of
parts which must be present in order that an animal may be placed in
the phylum to which we assume that it may belong. But these anatomical
parts need not actually be present in the fully developed organism:
thus there are Crustacea in which the body is not segmented, and in
which neither calcareous exo-skeleton nor jointed appendages are
present; and there are Vertebrata in which the limbs may be absent.
But in such cases we require evidence that the essential anatomical
characters which are absent in the fully developed animal have appeared
at some stage in its ontogeny, and this evidence is usually available.
Or if embryological evidence cannot be obtained, we require proof
that the animal can be traced backwards in time, by means of other
characters, to some form in which the missing structures reappear.
The schemata are thus the generalised or conceptual morphology of the
phyla. They are not the morphology of an individual organism, but they
include the morphology of the race.
They are, Bergson says, themes on which innumerable variations have
been constructed. Structural elements may be suppressed, as when the
notochord disappears in the development of the individual Tunicate,
though it is present in the larva. Or elements may disappear and become
replaced by other structures, as when the true molluscan gills are lost
in the Nudibranchs and are replaced by the respiratory plumes. They may
be reduced to vestiges, as in the case of the “pen” of the Squids, or
the “cuttlebone” of the cuttlefish, remnants of the domed shell of the
primitive mollusc; or in the appendix vermiformis of the human being, a
remnant of the voluminous cæcum of the herbivorous animal. Structures
which were originally distinct may coalesce, as when the greater number
of the primitively distinct segments of the thorax of the crustacean
fuse to form the “body” of the crab; or when the segmental ganglia of
the same animal fuse together to form the great thoracic nerve-centre.
The form and situation of a structure may vary within wide limits: thus
the digestive cavity of some Cœlenterates may be a simple sac, as in
the Hydra, but it may be partially subdivided by numerous mesenteries
as in the zooid of the Corals; or the simple tubular alimentary
canal in some Platyhelminth worms may be bifurcated in others,
triple-branched in others again, or even provided with numerous lateral
branches, as in the more specialised species in the group. Organs
originally simple may undergo progressive modification: thus the eye of
a mollusc may be a simple integumentary cavity in the floor of which
there are some simple nerve-endings, and some black pigment; or this
cavity may close up so as to form a sac, and the anterior part of the
sac may become transparent so as to form a cornea. Behind the cornea a
lens may be formed, and the simple terminal twigs of the nerve-endings
may become a many-layered retina of great complexity of structure. In
the lowest Chordates the central part of the blood-vascular system is
a simple contractile vessel, but this becomes the two-chambered heart
of the fish, the three-chambered heart of the reptile, or the powerful
four-chambered heart of the warm-blooded animal. Anatomical elements
may change in function; thus parts of the visceral skeleton in the fish
may become the ossicles of the middle ear in the Reptiles and Mammals;
while its swim-bladder may possibly be represented in the higher
vertebrates by the lungs.
Thus there may be suppression of parts leading to entire disappearance
or to mere vestiges of the original morphology. A structure
degenerating through disuse may become removed from its typical
relations with other structures and may acquire altogether new ones. Or
its increasing importance may lead to its hypertrophy and to increased
complexity of structure, and perhaps to the inclusion of new anatomical
elements, or to the incorporation of other parts, the function of which
may originally have been quite different. In all sorts of ways organs
and organ-systems may become anatomically different as the result of
adaptive modifications, or indirectly as non-adaptive modifications
induced by the adaptive modifications of adjacent parts. It is the task
of comparative anatomy to trace these changes of morphology, aided
by the study of embryology and by the comparison of the structure of
the parts of fossil animals. Regarding the process of transformism as
proved by experiments and observations in breeding and heredity, the
naturalist endeavours to trace the lines along which evolution has
proceeded from the results of morphological investigations.
Such results cannot have more than a very limited value, and it is
often the case that several interpretations of morphological results
are equally probable. We may conclude that the existing Teleost and
Elasmobranch fishes are descended from a common stock which no longer
exists; we may similarly conclude that the Birds and Reptiles are
closely allied, more so than either group is to the Mammals; and we
may conclude that the Primates--the group of Mammals to which Man
belongs--is descended from some group allied to the existing Ungulates
or Insectivores, while the Mammals themselves may have come down
from some group of vertebrates related to both the Amphibia and the
Reptiles. But as to the nature of the animals which combined the
characters of the Birds and Reptiles, or of the Reptiles and Amphibia,
we know nothing. Palæontology, if its results were more numerous than
they are, would afford us the material for the discovery of these
“missing links,” and there can be no doubt that as the world becomes
better known our knowledge of palæontological stages in the history of
existing groups will become more complete, so that we may, in time,
possess an actual historical record of the phylogeny of the main groups
of animals. But it is remarkable that while the results of comparative
anatomy and embryology, aided by those of palæontology, enable us to
trace back short series of stages in the evolutionary process, they
still show us gaps at all the places where lines of descent ought to
converge. They show us, for instance, that the oldest Birds known were
decidedly reptilian in their morphology, but they do not show us an
animal which was neither Bird nor Reptile, but from which both groups
of Vertebrata have descended; and this is almost always the case in
our hypothetical schemes of phylogeny. Morphology has continually
to postulate the existence of “annectant” forms, “Archi-Mollusc,”
“Protosaurian,” “Protochordate,” etc.: hypothetical animals which
combine the characters of those which lie near the bases of diverging
lines of descent. There is nothing to guide us in the construction of
these annectant forms except the progressive simplicity of structure
indicated in the morphological and palæontological series. The earlier
Birds had teeth, for instance, and so have the Reptiles, therefore the
annectant form had teeth, and it was an animal combining the schematic
morphology of both Birds and Reptiles. But just according to the value
which we attach to one morphological character rather than another,
so will the structure of the annectant form differ. Is, for instance,
the alimentary canal of the Vertebrate the most fundamental and
conservative part of its morphology: that is, is it the structure which
has been most resistant to change in the course of the evolutionary
process? Then we may regard the Vertebrates as having descended from
some animal which was closely related to the Annelid worms. Or is the
nervous system the most conservative part of the Vertebrate anatomy? If
so, we may trace back the main Chordate stem to animals which included
among their characters those of the most primitive Arthropods. In the
one case the annectant form joins together the Vertebrate and Annelid
stems, but in the other case it would join together the Vertebrate and
Arthropod stems, a conclusion which a rigid application of the results
of morphology would seem to make the more probable one.
[Illustration: FIG. 25.]
But, however this may be, we must not fail to notice that annectant
forms--“Archi-Mollusc,” “Protosaurian,” “Protochordate,” and the like,
are only fictions which we base on the precise importance that we
attach to one part of the essential morphology of a group of animals
rather than another. These hypothetical animals, and the genealogical
schemes or phylogenies of which they form the roots, are conventional
summaries of the results of comparative anatomy, this term being used
to include the anatomy of the developing animal and that of extinct
forms. So long as we do not possess a representative series of the
fossil remains of the animals which have existed in the past, all
schemes of descent founded on the comparison of the parts or the organs
of living animals, or on the comparison of stages of development, must
possess doubtful value when they profess to indicate the direction
taken by evolution. Their true value lies rather in the way they
epitomise our knowledge of morphology, and in the incentive which they
give to sustained and minute investigation of the structure of animals.
[Illustration: FIG. 26.]
Why did Haeckel’s “Gastrea-Theorie” gain the acceptance that it did
during the latter part of the nineteenth century? It correlated a
great number of facts, in that it postulated a general uniformity
of structure in the early developmental stages of very many animals
belonging to widely separated groups. In all of these the ovum segments
into a mass of cells, which then become arranged as a hollow ball
(_A_). One side of this ball becomes pushed in so that the inner
part of the hollow sphere becomes opposed to the inner wall of the
upper part. Thus a little sac, consisting of two layers of cells,
ectoderm and endoderm, and opening to the outside by an aperture, the
blastopore, is formed (_B_). This is essentially the anatomy of the
schematic Cœlenterate animal--_Hydra_, for instance, strongly suggests
it. Suppose now that the lips of the blastopore fuse together at one
place so that there are two openings into the cavity of the gastrula
instead of one; and suppose that the spherical organism elongates so
as to form a cylinder, the elongation involving the fused part of the
blastoporic region. Then we obviously have a worm-like animal with
an alimentary canal, a mouth and an anus (_C_). Suppose further that
an additional layer of cells becomes formed between the endoderm and
ectoderm by proliferation from one of these tissues, and suppose that
this becomes double and that a cavity appears between the two sheets of
cells forming this middle layer: this cavity becomes the body cavity
or cœlom (_D_). Now such blastula and gastrula stages appear in the
ontogeny of animals belonging to widely different groups, and such a
formation of the middle layer, or mesoblast, and of the mesoblastic or
cœlomic cavities also actually occurs. Let us assume therefore that
all multicellular animals have descended from a primitive Gastrea-form
essentially similar in morphology to the gastrula larva; and let us
assume that all cœlomate animals have descended from a form in which
a third layer of cells, or mesoblast, became intercalated between
the other two. These two assumptions are the bases of the classic
phylogenies of the last century; all Cœlenterate animals have descended
from a Gastrea-form, and all animals higher than the Cœlenterates have
been evolved from a three-layered form. Implied in this hypothesis is
also a third one, that the Gastrea-stage of evolution possesses such
a degree of stability that it has persisted, though in an obscure
condition it may be, in the development of nearly all multicellular
animals. The triple germinal layers, endoderm, ectoderm, and mesoderm,
which first became distinct from each other in the primitive cœlomate
animal, also acquired a high degree of stability, and they have been
transmitted by heredity to all animals higher than Cœlenterates. The
Gastrea and the three germinal layers are therefore to be sought for
in the developmental stages of all the higher animals, and they have
usually been found. Let it be admitted that they may make a transient
appearance--that they may be obscured in many ways, still they ought to
be there.
The Gastrea-Theorie ceased to be useful, as a means of description, or
a working hypothesis of investigation, after the rise of experimental
embryology. It could not be proved that the process of development
by gastrulation and the cleavage of a mesodermal layer are so very
conservative that they have persisted throughout the greater part of
the evolution of the animal world, yet without this proof it could not
be contended that the veiled gastrula of the developing frog’s egg,
for instance, is related genetically to the gastrula of the Echinoderm
larva. What experimental embryology does indicate is that the formation
of gastrula and (in most groups) the three germinal layers are only
the _means_ of morphogenesis. In the division of the ovum, and the
arrangement of the cells to form the organ-rudiments, the formation
of the gastrula and the mesoderm are in general the line of least
resistance in the process of development. If they do not appear, or
are difficult to recognise in the ontogeny of a group of animals, it
is not a sound method to assume their presence in an abbreviated or
distorted form, postulating that they _ought_ to be present, having
been transmitted by heredity. Physical conditions undoubtedly influence
developmental processes and there is no reason for assuming that all
ontogenetic processes were originally the same.
If we do not strain the facts of our descriptions of organic nature,
and if we do not build on unprovable conjectures, all that morphology
certainly shows us is that the evolutionary process has led to the
establishment of some dozen or so great groups of organisms, each
with appended smaller groups more or less closely related to them.
Whether these greater lines of descent are to be represented, as they
usually are, as branches springing from a single stem, or whether they
are truly collateral, each evolved independently of all the others,
is a question which is not to be solved merely by the methods of
comparative anatomy or embryology. The widely different, and equally
probable, phylogenies of the past indicate that data for the solution
of such a problem do not exist, not just yet at all events. What we
may discuss with greater advantage is the question as to which of
the great subdivisions of life represents the main results of the
evolution of complex organic entities from the simple living substances
in which we suppose life first became materialised on our earth. What
activities and structural forms represent the main manifestations of
the evolutionary process?
That is to say, what great groups of organisms are the _dominant_ ones
on the earth? Greater or less degrees of dominance are indicated by
the extent to which a group of organisms is distributed on the earth,
by its abundance, and by the period of time during which it can be
recognised in the fossil condition. Ubiquitous distribution implies
a high degree of adaptability: a group of organisms inhabiting land
and sea and atmosphere is obviously one in which the morphological
structure has been elastic enough to admit of the development of
various modes of locomotion; and the limbs may be either the appendages
of a terrestrial animal, or the fins, or other swimming organs, of an
aquatic creature, or the wings of one adapted for flight. Dominance
in this respect implies mobility and activity, and a relatively
highly developed nervous system; it implies the development of organs
specialised for prehension, that is, for the capture of food; and
it also implies a high degree of adaptability to widely different
physical conditions, to temperature changes, for instance. Dominance
in geological time means also this great adaptability to changes in
climatic conditions, and the development of means of distribution
sufficient to overcome extensive physical changes on the surface of the
earth. A terrestrial species might become isolated by the formation
of a mountain range, or the submergence of the land adjacent to that
which it inhabited, and some widely distributed species of plants and
insects must have been able to traverse oceanic areas. The abundance
of a group obviously implies great powers of reproduction, the ability
to withstand physical changes, and the ability to resist competition
with other predatory creatures. Dominance, in short, means that the
organism possesses in high degree the inherent powers of reproduction;
and also those activities which enable it to respond by adaptations of
morphology, functioning, and behaviour, to environmental changes. These
environmental changes are those which must have been experienced during
lengthy geological periods, and also those experienced by the organism
in its attempt continually to enlarge its area of distribution.
If we make a broad survey of the animal world we shall find that
dominance in these respects has been acquired by three great groups
of organisms, (1) the Bacteria, (2) the chlorophyllian organisms, (3)
the Arthropods, and (4) the Vertebrates. In each case the threefold
condition of wide distribution over all the earth, both in fresh and
marine water areas, on the land and in the atmosphere; of existence
throughout the greater part of geological time; and of ability to
withstand environmental change, are satisfied. The bacteria are known
to have existed in the carboniferous period. At the present time
their distribution on the earth is universal: no part of the land
surface, and no water masses, either marine or lacustrine--no matter
how unsuitable they may be for the life of more highly organised
creatures--are untenanted by bacteria. They are able to withstand
extremes of temperature, or of salinity, which would be fatal to the
multicellular plant or animal. Parasitism is a mode of life which they
exhibit in a more manifold degree than do any other organisms. The
upper regions of the atmosphere are the only parts of the earth and
its envelopes which they do not inhabit.
The chlorophyllian organisms include those unicellular plants and
animals--the distinction becomes obscure with regard to these
organisms--which are pigmented blue, green, brown, or red owing to the
existence in the cells of chlorophyll, or of some substance allied to
this compound, and they include, of course, the green plants. Like the
Bacteria their distribution is world-wide, extending over land and sea
and fresh-water areas; and it is restricted mainly by the distribution
of sunlight, and by a lower limit of temperature. The Marine Algæ, the
Diatoms, the Peridinians, and other chlorophyll-containing organisms
appear to inhabit all parts of the world ocean, certainly within a
depth of about twenty to fifty fathoms from the surface of the sea.
Green plants inhabit the land everywhere except within polar areas,
the tops of high mountains, and over areas desert by reason of lack of
water, or by the presence of mineral substances.
These conditions--temperature, light, soil, etc.--do not appear to
limit the distribution of the Arthropods and Vertebrates. We find
both kinds of animals in the deepest oceanic abysses (deep-sea fishes
and Crustacea), in polar land and sea regions (Man, some Insects,
Crustacea, and Birds), as well as in desert areas and on the summits of
the loftiest mountains. The Ants share the subsoil with the Bacteria.
Birds and Insects conquer the atmosphere by their activity and not,
like the Bacteria, merely by being blown about. Crustaceans such as the
Copepoda have much the same distribution in the sea as the Insects have
in the atmosphere, while Isopods and Amphipods are a parallel, so far
as the sea bottom is concerned, to the Spiders, Millipedes, and Ants on
the land. Fishes are distributed throughout all depths, and in almost
all physical conditions in the sea. Some species of marine Mammalia
and Birds are quite cosmopolitan except that they are restricted to
the upper layers of the ocean. Land Mammals are subject to the same
restrictions as are the green plants, being unable to survive in desert
and polar areas. The only parts of the sea which are not inhabited by
Arthropods and Vertebrates are those limited deep strata of water (as
in the case of the deeper layers of the Black Sea) where there are
accumulations of poisonous chemical substances in solution. But the
Bacteria inhabit even these regions.
Green plants, Arthropods, and Vertebrates appear as fossils in almost
every part of the stratified rocks. The Trilobites represent the end of
a long evolutionary process, and the same is to be said of the first
fishes found in Silurian rocks, so that these groups of animals must
have existed in the geological periods represented by those remains
of rocks which are older than the earliest fossiliferous ones. Plant
remains are present in Silurian rocks, but there can be no doubt that
Ferns and other chlorophyllian organisms must have been in existence
long before this time. We can hardly suppose that the Bacteria found
in the Carboniferous rocks first appeared at this time in the earth’s
history: like the other great groups of life they probably had a
prolonged history prior to that date of the geological formations in
which they are first to be recognised. Our dominant groups of organisms
may therefore be traced back almost to the very beginnings of life on
the earth.
Dominance, such as we have defined it, cannot be said to have been
attained by any other of the sub-kingdoms of life. Cœlenterates and
sponges appear to have existed throughout the whole period during
which the remains of organisms are to be traced in the rocks, but
they have always been exclusively aquatic animals and they are very
sparsely distributed in fresh water regions. Echinoderms are also a
very old group, but they were more abundant in the past than they
are now, and they appear to have been an exclusively marine group of
animals. Molluscs have existed since the beginnings of stratified
deposits and they are both aquatic and terrestrial animals, but they
belong predominantly to the sea. They have always been relatively
sluggish and inactive animals, with the exceptions of the great Squids
and Cuttlefishes, but fortunately for the other inhabitants of the
sea these formidable creatures appear to possess restricted powers of
reproduction, and they have never been very abundant. All the smaller
groups of animals are restricted in their distribution: the flat-worms
occur sparingly both on the land and in the sea, and they attain their
highest development as parasites in the bodies of other animals.
Annelid worms, Gephyrea, Nemertine worms, Polyzoa, Rotifers, etc., are
all groups of animals occurring mainly in fresh and sea water and none
of them is abundant. Related to most of the great phyla are smaller
groups: the extinct Trilobites, Eurypterids, etc., in relation to the
Arthropoda; the group represented now by _Peripatus_ in relation to the
Arthropods and Annelids; the Enteropneusta and some other creatures
which appear to possess affinities with the Echinoderms and Chordates;
and the extinct Ostracoderms, which appear to have been related to
either the Arthropods or Vertebrates, or to both. All these smaller
groups of animals we must regard as representing sidepaths taken by
the evolutionary process--paths which have either ended blindly, as in
the case of those groups which have become extinct, or which we can
still trace in the existing remnants of groups which were formerly more
abundant than they are now.
Only among the existing Bacteria, chlorophyllian organisms, Arthropods,
and Vertebrates has the vital impetus found its most complete
manifestation, and we may even narrow down the main path that evolution
has taken to certain groups in each of these phyla. Some of the
Bacteria--those which are exclusively parasitic in the bodies of the
warm-blooded animals--have adopted a most specialised mode of life,
and may even be said to exist only with difficulty, since the healthy
animal is able to destroy them. Only those Bacteria living in the open
or upon the dead tissues of plants and animals have attained to real
dominance. Some green plants, like the Ferns, are far less abundant now
than they were in the past; while the Fungi and some other saprophytic
and parasitic plants have specialised in much the same way as have the
parasitic worms, and are restricted in their distribution. Marine Algæ
are confined to a relatively narrow selvedge of sea round the land
margin. The great trees, the grasses, and the microscopic green plants
such as the Diatoms and Peridinians, represent the truly dominant
organisms in the vegetable kingdom. On the side of the Arthropods and
Vertebrates there have been many unsuccessful lines of evolution: the
Trilobites, for instance, in the former group; and the armoured Ganoid
fishes, the armed Reptiles, the volant Reptiles, and the giant Saurians
and Mammals among the Vertebrates. Among the existing Arthropods and
Vertebrates there are some smaller groups which persist, so to speak,
only with difficulty. Such are the Spiders, Mites, and Scorpions among
the Arthropods; and the Tunicates, the Dipnoan fishes, the tailed
Amphibians, many Reptiles, and the volant Mammals among the Chordates:
such are, of course, only instances of the less successful lines of
evolution in these phyla. The dominant Arthropods and Vertebrates are
the Crustacea, the Hymenopterous Insects, the Teleost and Elasmobranch
fishes, and the terrestrial Mammals. The earth belongs to Man, to
the social and solitary Ants, Wasps and Bees, the marine Crustacea,
the Teleost fishes, the Trees, Grasses, and unicellular Diatoms and
Peridinians, and to the putrefactive and prototrophic Bacteria.
These are the organisms in which life has attained its fullest
manifestations, and has been most successful in its mastery over inert
matter.
In what kinds of activity and morphology, then, has the vital impetus
found most complete expression? We see at once that in relation to
energetic processes life has followed two divergent lines--animal
and vegetable. There is no absolute distinction between the
energy-transformations which proceed in the living plant and animal--we
return to this point later on--but we may trace an unmistakable
difference in tendency, that is, in the direction taken by evolution.
This difference we have already considered in an earlier chapter, but
we may illustrate it by considering a lifeless earth, and also one
tenanted only by plants, or animals, or by both.
In a lifeless earth all energetic processes would tend continually
toward a condition of stability. The crust of the earth, that is, the
part known to us by direct observation, is made up of rocks and the
remains of rocks; materials consisting of compounds of oxygen, silicon,
iron, aluminium, sodium, potassium, calcium, and so on. They are
substances which would be stable but for the eroding action of water,
the gases of the atmosphere, and volcanic activity. But as volcanic
activity tends always toward cessation, the oxygen of the atmosphere
would gradually disappear, first by its combination with oxidisable
substances, and second by its combination with the nitrogen of the
atmosphere under the influence of electric discharges. Carbon dioxide
would either combine with materials in the rocks, or would remain in
the atmosphere along with nitrogen and other inert gases in a stable
condition. Water, moved by the tides and winds, would gradually plane
down the surface of the land, unless along with other gases it would
gradually become dissipated into outer space. We see, then, that the
materials of the earth tend to fall into stable combinations, and that
they approximate toward conditions in which potential chemical energy
becomes reduced to a minimum, the whole energy possessed by matter
being that of the motions of the molecules, that is, kinetic energy
unavailable for transformations of any kind. It would be an earth
devoid of phenomena.
Vegetable life alone would be possible only for a time on an earth such
as we know it at present. The green plant depends for its existence on
the presence in the soil of mineral substances such as salts of nitric
acid and of ammonia, and on the presence of water and carbon dioxide in
the atmosphere. The chlorophyllian apparatus is essentially a mechanism
whereby these substances become built up into carbohydrates, like
starch and sugar; hydrocarbons, like resins and oils; and proteids. The
energy necessary for these syntheses is obtained from solar radiation
through the agency of the chlorophyll plastids. The green plant would
depend for its supply of nitrate or ammonia on the combination of the
nitrogen of the atmosphere with oxygen, or on the exhalations from
volcanoes, and these are irreversible processes which tend continually
toward cessation. The plant requires also carbon dioxide and the amount
of this substance in the atmosphere is very limited, while the only
inorganic source from which it can be renewed seems to be volcanic
activity: this substance also would tend to disappear. A time would
therefore come when plant life on the earth would cease to be possible
because of the disappearance of the materials on which it depends; but
while it did exist its result would be the accumulation of chemical
compounds of high potential energy. The result of the metabolism of
the plant is the formation of such compounds as cellulose from woody
tissues and shed leaves, of other plant carbohydrates, of oils and
resins, and of proteids. In the absence of bacteria such substances
would persist unchanged: even in an earth tenanted by bacteria such
products as oils, lignite, peat, coal, etc., have been able to
accumulate throughout geological time. The tendency of plant life
is therefore toward the accumulation of compounds of high potential
energy, and this process also is irreversible.
Bacterial activity would, of itself, make continued plant life possible
on the earth. The essential characters of these organisms are their
ability to bring about the most varied energy-transformations. From
our present point of view bacteria may be divided into paratrophic,
metatrophic, and prototrophic forms. Paratrophic bacteria are those
which live as parasites within the living tissues of plants and
animals: this mode of life is obligatory, and these organisms are
unable to live in the open. The result of their activity is the
breaking down of protoplasmic substance. Metatrophic bacteria are
those that produce putrefaction and fermentation of organic compounds.
They may be parasitic in their mode of life, but most of them live in
soil, in water, and in the cavities of the animal body--the mouth,
alimentary canal, nose, and vagina. Proteids are decomposed by them
into simple chemical compounds such as amido-acids, and then these
substances, along with carbohydrates, are fermented so as ultimately
to form water, carbonic acid, and salts of nitric acid. These bacteria
obtain their energy from the conversion of chemical compounds of high
potential energy into compounds of low potential energy. Prototrophic
bacteria are never parasites, nor do they live in the cavities of the
bodies of animals: they always live in the open. They carry on still
further the action of the putrefactive bacteria by converting ammonia
into nitrous acid, and nitrous acid into nitric acid. Others reverse
this series of changes by reducing nitric acid to nitrous acid, nitrous
acid to ammonia, and ammonia to free nitrogen. Others again oxidise
sulphuretted hydrogen to sulphuric acid, others ferrous hydrate to
ferric hydrate, while it has recently been shown that some bacteria
are apparently able to oxidise the carbon of coal to carbonic acid.
Some are able to oxidise the free nitrogen of the atmosphere into
nitrous and nitric acids. How precisely the energy necessary for these
transformations is obtained is not at all clearly understood, and it
may be possible that some of the prototrophic bacteria obtain their
energy by making use of the un-co-ordinated kinetic energy of the
medium in which they live. From our point of view the net result of the
activity of the predominant species of bacteria which inhabit the earth
is that they _reverse_ the processes which are the manifestations of
the metabolism of plants and animals. The result of the metabolism of
plants is the accumulation of stores of high potential compounds such
as carbohydrates, and the depletion of the terrestrial stores of carbon
dioxide and other materials necessary for the continued existence of
the plants themselves. The result of the metabolism of the bacteria is
the break-down of this accumulation of such compounds as carbohydrates,
and the replenishing of the stores of carbon dioxide and nitrogenous
mineral substance on which the plant depends. If bacteria are present,
the life process becomes a reversible one.
Plant life and bacterial life are thus complementary to each other,
for, on the whole, the energetic processes of the green plant proceed
in the opposite direction to those of the bacteria. An organic world
consisting of green plants and bacteria would therefore be one capable
of permanent existence. Now, so far, we need only consider these
various kinds of organisms as living protoplasmic substances in which
energy-transformations of different types proceed. The bacterium is
simply a cell containing a nucleus, and the green plant need only be
a nucleated cell containing a chlorophyll plastid: this is, indeed,
all that it is in the case of a Diatom or a Peridinian. The morphology
of the green plant is only accessory to the chlorophyllian apparatus.
Neglecting the reproductive apparatus, the higher green plant consists
essentially of the chlorophyllian cells in the parenchyma of the leaf,
for roots and stomata are only organs for the absorption of water and
mineral salts from the soil and carbon dioxide from the atmosphere;
while the tissues of the trunk, stems, and branches are, in the main,
apparatus for the conduction of these raw materials through the body
of the plant, and, of course, the nutritive substances into which they
are elaborated. All the innumerable variations of form in the plant
(apart from the structure of the flower or other reproductive organ)
are adaptations which provide for the absorption and distribution of
these substances; or for the mechanical support of the plant body; or
are non-adaptive variations, pure luxuries, so to speak.
More than this is represented by the structure of the animal body, but
we must first of all consider the points of difference between plant
and animal regarded merely as apparatus in which energy-transformations
occur. In the green plant energy is accumulated in the form of
high potential chemical compounds, but in the animal energy is
expended. Inorganic mineral substances are built up by the plant
into carbohydrate, proteid, and fat or oil, but in the animal body
carbohydrate, proteid, and fat are dissociated into water, carbonic
acid, and urea (or some other nitrogenous excretory substance); and
the urea or other analogous substance is broken down by bacteria into
nitrate, water, and carbon dioxide. The metabolic activities of the
animal are said to be “analytic” or destructive, while those of the
plant are said to be “synthetic” or constructive, but these contrasting
terms hardly describe accurately the essential nature of the activities
of the two kinds of organisms. What further constitutes “animality”? It
is _purposeful mobility_, and the energy-transformations that occur are
the means whereby this mobility is attained. The plant is essentially
immobile, for such movements as the turning of leaves toward the
light, the down-growth of roots, the up-growth of stems, the twining
of tendrils round supporting objects, and the opening and closing of
flowers are only the movements of parts of the plant organism. They are
constant, directed responses to external stimuli--real tropisms--and
the extension of this kind of response so as to describe in general the
movements of animals is only an instance of the insufficient analysis
of facts. The movements of the typical green plant are therefore
movements of its parts, they are few in number, they belong to a few
simple types, and they are evoked by simple external physical changes
in the medium. The movements of the typical animal are movements of the
organism as a whole; they are infinitely varied in their nature; they
are evoked by individualised stimuli and they are continually being
modified by the experience of the organism.
The bodily structure of the animal is the means whereby this purposeful
mobility is attained and the energy-transformations directed; and
the greater and more varied the movements of the animal, the more
complex is its structure. In respect of the manner in which the
energy-transformations are effected, that is, in respect of the
material means whereby energy falls from a state of high potential to a
state of low potential, the morphology of the animal is similar to that
of the plant, that is, the energy-transformations are the functions of
nucleated cells. But in the plant the kinetic energy of solar radiation
passes into the potential energy of chemical compounds which become
stored in the body of the plant; while in the animal the potential
energy of ingested chemical compounds passes into the kinetic energy
of the movements of the animal itself. How exactly it moves, how this
kinetic energy is employed is determined by the sensori-motor system.
It is the existence of the sensori-motor system that makes the animal
an animal. What, then, is the sensori-motor system? It is the skeleton
and muscles, that is, the organs of locomotion, aggression, prehension,
and mastication; the peripheral sensory and motor nerves; and the
central nervous system or brain. The skeleton of an animal, whether
it be the carapace or exoskeleton of a crustacean, or the vertebral
column, limb-girdles, and limb-bones of a vertebrate, is a rigid and
fixed series of supports to which the muscles are attached. Organs
of locomotion are, for instance, the appendages of a crustacean, the
wings of a bird or insect, the tail and fins of a fish, or the limbs
of a vertebrate. Organs of aggression are the mandibles of a spider
or blood-sucking fly, the chelate claws of a crab or lobster, the
jaws of a fish, or the claws and teeth of a terrestrial vertebrate.
Organs of prehension and mastication are in the main also those of
aggression. All these parts consist of modified skeletal structures,
teeth, claws, etc., attached to muscles which originate in the rigid
parts of the skeleton. When we speak of the movements of an animal we
speak of the motions of such parts as we have mentioned; other parts do
indeed move--the heart pulsates, the lungs dilate and contract, and the
blood and other fluids circulate through closed vessels; but these are
movements of the parts of the animal, and are comparable rather with
those movements of the plant organism that we have considered. They are
not to be regarded as examples of the mobility of the animal in the
sense of the exercise of its sensori-motor system.
A central and peripheral nervous system is, of course, bound up with
a motor system. Receptor organs, eyes, olfactory, auditory, tactile
organs of sense, and so on, are the means whereby the animal is
_affected by_ changes in its environment--it need not be cognisant
of, or become aware of, or perceive these impressions on its receptor
organs. These stimuli are transmitted along the sensory, or afferent,
nerves to the central nervous system: this is the way in. The effector
nervous organs are the motor plates, that is, the nervous structures in
the muscles in which the nerves terminate. The motor nerves are the
efferent paths, the way out from the central nervous system.
The central nervous system is essentially the organ for the integration
of the activities of the whole body. It is the “seat of multitudinous
synapses,” a description which better than any other applies to the
morphology of the brain of the vertebrate animal. We have already
considered what is meant by the term “reflex action,” it is the series
of processes which occur when a “reflex arc” becomes functionally
active. A reflex arc consists of (1) a receptor organ, say a tactile
corpuscle in the skin; (2) an afferent nerve fibre; (3) a nerve cell
in the brain or spinal cord; (4) an efferent nerve fibre; and (5) an
effector nerve organ, say a motor plate in a muscle fibre. The series
of processes involved in a reflex action consist of the stimulation
of the receptor organ, the passage of the afferent impulse into the
brain or cord, the passage of the impulse through a series of cells in
the nerve centre forming a synapse, the transmission of the impulse
through the efferent nerve fibre into the effector organ in the muscle
and the stimulation of the latter to an act of contraction. This is a
purely schematic description of the structures and processes forming
a reflex action and arc: in reality the path both into and out from
the central nervous system is interrupted again and again, and at each
place of interruption there are alternative paths. The interruptions
occur at the synapses. At a synapse the nervous impulse passes through
an arborescence of fine nervous twigs, into which the fibre breaks
up, into a similar arborescence, and these two arborescences are not
in actual physical contact: the impulse leaps over a gap. At numerous
places in both brain and cord there are alternative synapses and at
these places the impulse may travel in more than one direction.
The brain and cord are a switch-board of unimaginable complexity, so
that an efferent impulse entering it from, say, the eye, can be shunted
on to one nerve path after another, so that it may affect any muscle
in the whole body. This is no fiction: it may actually be the case.
In normal respiration a centre in the hind-brain is stimulated to
rhythmical activity by the presence of carbon dioxide in the blood, and
from it efferent impulses originate which stimulate the muscles of the
chest wall and diaphragm. But in the distress of asphyxia every muscle
of the body may be stimulated to activity in the effort to accelerate
the oxygenation of the blood, and these are not spasmodic movements
of the muscles of limbs, etc., but purposeful contractions having for
their object the increased intake of air into the lungs. The central
nervous system is, therefore, a switch-board--so mechanistic physiology
teaches, neglecting any idea of an _operator_. But the whole trend of
modern investigation is to show that every increase of specialisation
in the evolution of the higher animal adds to the complexity of this
nervous apparatus by increasing the number of alternative paths that an
impulse originating anywhere in the body may take before it issues from
the brain or spinal cord. Yet with all this increase of complexity it
is nevertheless the case that in the higher animal the various parts of
the central and peripheral nervous system are more and more integrated,
so that in the actions of the animal it becomes more and more the
organism _as a whole_ that acts.
All other organs in the animal body--excepting always the reproductive
apparatus--are accessory to the sensori-motor system. The alimentary
canal and its glands dissolve the food-stuffs ingested; the metabolic
organs, that is, the cells of the wall of the intestine, the liver,
etc., transform these ingested proteids, fats, and carbohydrates of the
food into the proteids, fats, and carbohydrates of the animal itself;
the heart, blood, and lymph vessels carry this food material to the
muscles and nervous organs; the respiratory organs absorb oxygen which
is distributed throughout the body in the blood stream; the excretory
organs, that is, the lungs, skin, and kidneys, remove noxious materials
like carbonic acid and urea, or its precursors; and purposeful changes
of functioning of all these organs are brought about by changes in
motor activity. Round the sensori-motor system all the rest of the
structure of the animal body is built up.
What we see clearly in the evolution of the animal body is the
progressive increase of activity of the sensori-motor system. The
_animal becomes more and more mobile_. It is in this way that dominance
has been attained and all the directions of structural evolution in the
past that have not tended in this direction have been unsuccessful,
irreversible, evolutionary processes. Great size has not succeeded in
the animal kingdom, and so the gigantic reptiles and mammals of the
secondary and tertiary periods have become extinct. Defence against
enemies by the development of dermal armour has not succeeded, and so
the Dinosaurs, and other armed animals of the Tertiary Age have also
become extinct. The transformation of the fore limbs of the reptile
into wings, or the legs of the mammal into flappers, did not succeed,
because all the rest of the structure of these animals had become
adapted to locomotion on dry land, and the change of structure had
become too profound to be modified: so the Pterodactyls passed away,
as the whales of our own period are also passing. Only in the lightly
boned, feathered bird, with the possibility of the development of
powerful pectoral muscles, did indefinite possibilities of flight
reside; and only in the fish, with the concomitant evolution of gills,
the reduction of a minimum of the mass of the alimentary canal and its
glands, and the conversion of most of the muscles of the body into
organs actuating the tail fin, was the completeness of adaptation
to aquatic life realised. Mobility, a bodily structure capable of
indefinitely varied movements, and a nervous system by the aid of which
any part of the body might become linked to any other part--these were
the structural adaptations that have been successful alike in Arthropod
and Vertebrate.
There were apparently two main types of structure by means of which
this mobility and elasticity could be attained, the Arthropod type
and the Vertebrate type. There seems little to choose between them
if we had to select one of them in order to obtain a highly mobile
organic mechanism. Arthropod and Vertebrate seem to be equally complex
if we take account of difference in size and the additional bodily
mechanism that great size must involve. Certainly the musculature of
the Vertebrate is more complex than in the Arthropod. But greater
weight must require larger and more powerful muscles if the same degree
of mobility relative to the size of the animal is to be attained,
and this more complex musculature must carry with it a more complex
brain. It must also be concomitant with a more massive skeleton, for
rigid supports for the muscles must be present in the mechanism. Why
are there no great insects or crustaceans? Mr Wells has suggested in
one of his novels the formidability of a wasp two feet long! Such a
creature would indeed be more dreadful than any predatory bird that we
know if its activity were also that of the wasps that we know, just as
a Copepod as large as a shark would be a more formidable animal than
the fish. It seems possible that the reason for the smaller size of
the Vertebrate is to be found in the nature of the skeleton. Powerful
muscles would require a very strong and thick carapace, and this would
attain a mass in a very large insect or crustacean which would require
too much energy for its rapid transport. A rigid exoskeleton like that
of an Arthropod also means that growth must take place by a process
of ecdysis, that is, the animal grows only during the periods when it
casts its shell; and the necessity of this process of ecdysis must
be a formidable disadvantage in the case of a very large animal, if
indeed it would be possible at all. Thus the Arthropod developing an
exoskeleton must remain small, and this smallness, fortunately for the
Vertebrate, has made it the less formidable animal. It was an accident
of evolution that the Arthropods developed an exoskeleton instead of an
endoskeleton.
Undoubtedly the internal skeleton of the Vertebrates, with its light,
hollow, cancellated bones, was mechanically the best means for the
attachment of muscles. It made possible a greater degree of freedom
of movement of the parts of the body, greater variety and plasticity
of action, and it removed, to some extent, the limit of size and the
embarrassing discontinuity of growth by ecdysis, with all the dangers
that this involves. Above all, it led to the increased complexity
of the central nervous system, since this became bound up with the
increasing variety of bodily movement.
In the evolution of the dominant groups of organisms we see, then, the
development of several tendencies. First, that tendency which seems
to offer the greatest contrast to the universal tendency displayed in
inorganic processes, the dissipation of energy. The plant organism is
essentially a system in which energy is accumulated in the potential
form. Then, in the animal kingdom we see that the main tendency of
evolution has been the development of systems in which energy becomes
expended in infinitely varied movements. It may seem, on superficial
examination, that in the animal mode of metabolism energy is dissipated
as it is in inorganic processes; and this is the conclusion that we
should reach if we considered the actions, and the results of the
actions, of the lower animals only, that is, animals lower than man. We
return to this point later on, but in the meantime it is to be noted
that the fundamental division of organisms is that founded upon their
activities as energy-transformers, that is, into plants and animals.
Within each of these kingdoms of organisms structural evolution has
occurred: the unicellular green plant has evolved along very numerous
lines, each of them characterised by a different type of morphological
structure. The unicellular animal has also evolved in a similar way
with the result that the present phyla have become established. Looking
at these great groups of animals, we see that two of them have attained
dominance by the development along different lines of a sensori-motor
system. Here we see another fundamental difference between the
plant and animal organism, but one which is a consequence of the
difference that exists between the two kingdoms in respect of the
energy-transformations carried out by them. The plant is characterised
by immobility, the animal by mobility.
Immobility implies unconsciousness, mobility consciousness, and this
physical difference is the third one which we can establish between the
plant and the animal. Now few physiologists are likely to accept this
distinction as one which has any real objective meaning. Consciousness
is not a concept to be dealt with in any process of reasoning, it is
not even something felt in the way in which we speak of the feelings of
pain, or light, or hunger: these are all states of our consciousness.
The difference in ourselves, says Ladd, when we are sunk in sound
dreamless sleep, and when we are in full waking activity, _that_ is
consciousness. If we reason about organisms and their activities
as we do about inorganic things we have no right to speak about
consciousness, for outside our own Ego it has no existence. The acting
animal is only a body, or a system of bodies, moving in nature, and all
its activities are to be described by a system of generalised force
and position co-ordinates with reference to some arbitrarily chosen
point of space. “This animal machine,” says a zoologist, writing about
instinct, “which I call my wife, exhibits certain facial contortions
and emits certain articulate sounds which correspond with those emitted
by myself when I have a headache, but I have no right to say that she
has a headache.” This kind of argument does not appear to be capable
of refutation except, perhaps, by the domestic conflicts which it
would usually evoke if applied in such cases as that quoted. In a
description of nature by the methods and symbolism of science we see
only systems of molecules in motion, and in those systems which we
describe as organisms the motions are only more complex than they are
in inorganic systems. Such is the method of science, as irrefutable
in the study of the organism as we know that it is false. Valid in
pure speculation according to the methods of the intellect it would
nevertheless be absurd in the everyday affairs of common civilised life
and the scientific man who applies it in his writing would nevertheless
hesitate to apply it in the affairs of his own household.
We must recognise that our knowledge that other beings like
ourselves, as well as animals lower in organisation than ourselves,
are consciously acting organisms is intuitive knowledge, attainable
because of community of organisation: our intuitive knowledge of the
behaviour and feelings of our own brothers and sisters is greater
than our knowledge of other men and women; and we can, by intuition,
place ourselves within the consciousness of an intelligent dog to a
greater extent than in the case of other animals. This knowledge of
the consciousness of other animals is not scientific knowledge and it
is unattainable and unprovable by reasoning or methods of scientific
observation. It is a conviction in itself incapable of analysis or
proof, but yet a conviction on which we confidently base most of our
dealings with our fellow-creatures, and which is justified by our
experience.
It is nevertheless a scientific hypothesis of much the same validity as
many other scientific hypotheses. We cannot bring ourselves to doubt
that other men and women are consciously acting organisms, however
impossible it may be to adduce scientific reason for the faith that
is in us. We cannot doubt that a compass needle which “responds” by
turning one or other of its poles towards us according as we push
forwards one or other of the poles of a magnet is an unconscious
piece of metal, though we find it impossible to say why this belief
possesses such conviction. From this to the movements of the typical
green plant is only a step. The turning of a green leaf towards the
source of light, or the downward movement of a root into the soil, are
responses to external stimuli which exhibit most of the inevitability
of response of the magnet. They are “tropisms”: the plant leaf is
obliged to turn towards the light so that the latter strikes against
its surface perpendicularly, and the root must grow downwards because
gravity acts along vertical lines. But suppose that reflex actions are
tropistic: suppose, for instance, that the moth is bound to fly into
the candle flame because the light stimulates both sides of its body
equally and this orientates it and guides it towards the direction from
which the stimulus proceeds. Complex actions, in the higher animal, on
this view are chains of reflexes, and the acting must be unconscious
and inevitable, just as the turning of the magnet or green leaf are
unconscious movements. Therefore the actions of our fellow-creatures
are unconscious and automatic, a conclusion toward which the whole
tendency of mechanistic physiology forces us. Yet we know that the
conclusion cannot be true.
Between the obligatory reaction of the compass needle to the magnet, or
the analogous heliotropism and geotropism of the plant organism, and
the infinitely variable responses of the higher animal toward changes
in its environment, consciousness must come into existence. It is
absent in the inorganic system and the typical green plant; it is dim
in the sedentary sea-anemone or mollusc; it becomes brighter in the
freely moving Arthropod or fish; and it is most intense in man. This,
it must be admitted, is only a belief, but accepting it as such we may
attempt to support it by showing a parallelism of stages of structural
complexity and actions. The sensori-motor system is absent in the
green plant; it is simple in the extreme in the sea-anemone; and it
is rudimentary or vestigial in the sedentary mollusc. It becomes more
complex in the Arthropod or fish, and it is developed to the greatest
degree in ourselves. If we now examine our own mental states, with
their corresponding conditions of bodily activity, we see as clearly as
possible that our consciousness waxes and wanes with our activities.
It is absent in normal sleep, when bodily activity in the real sense
ceases almost absolutely, when the cerebral cortex becomes inactive,
and when the only movements performed are those truly automatic ones
of parts of the body which are analogous to the movements of the plant
organism. Such movements are the rhythmic ones of the heart and lungs,
the movements of the blood, and so on, in general the movements leading
to constructive metabolism. Consciousness is most intense in difficult
unfamiliar actions: the lad learning to row; the child learning scales
on the piano, or the fingering of the violin; the engineer assembling
together the parts of a new machine; or the artist engaged on a
picture. In each of these cases the worker is acutely conscious, in a
deliberative manner, of his own bodily actions. But with the habitual
exercise of these movements, and with the ease and facility with which
they are performed, consciousness that they are being performed fades
towards nothingness.
What does this mean but that degrees of consciousness are parallel to
degrees of complexity of deliberated and purposeful bodily movements
or actions? Or degrees of consciousness are also parallel to the
attempt of the organism to perform these actions. What is pain, the
most acutely felt of all our mental states? It is, Bergson says, the
consciousness of the persistent and unsuccessful effort of the tissues
to respond purposefully to a persistently renewed stimulus. But complex
actions require for their performance systems of skeletal and muscular
parts capable of moving in the most varied ways, and a system of
afferent and efferent nerves with all their connections in the central
nervous system: that is, a sensori-motor system. Therefore just as
the sensori-motor system is more or less complex so, in general, is
consciousness more or less acute.
Yet in the same organism consciousness is the more or less acute as
the actions which it performs are more or less familiar. The pianist
who plays scales as a matter of exercise carries out most complex
movements of hands and wrists unconsciously and without effort, but
to play an unfamiliar composition for the first time without error
involves attention of the highest degree. A girl who counts the sheets
of paper coming from a machine seizes a handful in one hand, and drops
a separate sheet between every two fingers of the other hand, repeating
this most difficult operation with great rapidity, and counting the
handfuls of sheets accurately while thinking and talking deliberately
about some other matter. At the beginning of her work these actions
were clumsily performed and facility was only attained by sustained
attention to the movements of the hands, yet with experience they
become unconsciously performed. Complex movements of the body and limbs
and digits, involving the co-ordinated activity of numerous muscles,
nerves, and nerve centres, are performed at first only after a high
degree of conscious effort, but with each repetition of the series of
movements the animal ceases to be aware of them, or at least of their
difficulty. In the higher animals there are, therefore, two categories
of actions, (1) those unfamiliar actions which are _difficult_, and
in the performance of which the animal becomes conscious of complex
muscular activities; and (2) those habitual actions which have
become _easy_ by dint of repetition, and the performance of which is
unattended by conscious effort. Analysis of our own activities reveals
these two categories of actions, and we have no doubt whatever that the
higher animals have the same feelings of difficulty and effort in the
one case, and of lack of conscious effort in the other.
The difference is one of those which separate instinctive from
intelligent activities. Now we hesitate to attempt the discussion of
this much-controverted question of the distinction between instinct and
intelligence: after reading much that has been said as to the nature of
this difference, one rises with the uncomfortable impression that the
time is not yet ripe for its discussion, and that the problem is still
one far more for the naturalist than for the psychologist. Reliable
data are still urgently required. Yet it is a question which we cannot
fail to consider. The typical plant differs from the typical animal in
that a sensori-motor system has been evolved in the one but not in the
other; and among the animals in which this system is developed to a
high degree the activities which involve its exercise differ in their
form. Actions of a stereotyped pattern characterise the behaviour of
the higher Invertebrate, while in the higher Vertebrate all that we
see indicates that the behaviour is the result of deliberation, and
that the actions performed are not stereotyped but differ infinitely
in their patterns. Just as clearly as differences in morphology
differentiate Arthropod from Vertebrate, so also do differences in the
mode of activity of the sensori-motor system mark divergent lines of
evolution culminating in the Hymenopterous Insect on the one hand and
in Man on the other.
What is the essential difference between an action performed
instinctively and one performed intelligently? It is not that the
animal is unaware of its activity in the first case and not in the
second; however much we tend to “explain” organic activity in terms of
inorganic reactions, we do not really believe that the instinctively
acting wasp is a pure automaton, while admitting that the schoolgirl
is acutely conscious of her own multifarious activities. It is not
that the instinctive action displays a “finish,” or perfection of
technique, that the deliberative action lacks: the comb built by the
wasp is not more perfect in its way than is the doorway constructed
by a skilled mason, or the “buttonholes” stitched by a seamstress.
It is not that instinctive actions are so absolutely stereotyped, as
is sometimes assumed, while intelligent actions grow more perfect in
their result by repetition: the work of the insect or bird is often
faulty and it is improved by practice. The most obvious difference is
that the instinctive action is _effective_ the very first time it is
performed, while the intelligent action only becomes effective after it
has been attempted several times, or very many times, according to its
difficulty. The flight of the young swallow is effective inasmuch as it
sustains the bird in the air, but it is also an exceedingly difficult
series of muscular efforts which is at first clumsily performed
and which becomes more perfect by repetition. But the flight of an
aeroplane, even now after years of experiment, is not always effective,
and exhibits at its best all the imperfections of the flight of the
young swallow. Yet can we doubt that in time it will exhibit all the
ease and certainty and finish of the flight of the bird?
The typical intelligently performed action is the action of a _tool_,
or of a part of the body which is used for some other purpose than
that which is indicated by its immediate evolutionary history, or by
its previous use. The typical instinctively performed action is always
the action of a bodily organ, the structure and immediate evolutionary
history of which indicates that it originated as an adaptation for
the performance of these particular actions, or category of actions.
Here it seems to us that we find the distinction between the two kinds
of bodily activity; and the distinction is one which depends for its
validity on our notions as to what a tool is. An implement made by man
is a piece of inert matter fashioned in order that it may be used for
a definite preconceived purpose. It has an existence as a definite
specific object _apart from its use_; and its exercise by the man who
made it and its existence in nature are two different things. Its use
must be _learned_, and the results obtained by its employment become
more perfect with every repetition of its use. But the mandibles of an
insect are implements purposefully adapted for some action or series
of actions, just as the pincers of the blacksmith are so adapted.
They are, however, implements which are part of the organisation of
the animal using them--organised tools--and it does not seem as if we
ought to think of them, and of their shape and nature, as something
apart from their exercise. Must we think of an animal as having to
_learn_ how to use any part of its body? If so, then the problem of
instinct remains with us in all its historic obscurity. But if we think
of the existence of a bodily tool as something inseparable from the
functioning of the tool, the problem becomes less obscure, or at least
it can be stated in terms of some other problems which we have already
considered.
We do actually think of bodily parts or organs as material structures
quite apart from the consideration of their functions: it is the
distinction between morphology and physiology--an altogether artificial
one. An animal, for the morphologist, is a complex of skeleton,
muscles, nerves, glands, and so on; and it does not matter whether
it is contained in a jar of methylated spirit or is running about in
a cage. For the physiologist it is “something happening”; but is it
not really both things, and are not the structure and the functioning
only two convenient, but arbitrary, aspects from which we consider the
organism? We ought not to think of diaphragm and lungs apart from the
movements of these organs, and we do not say that the first breath
drawn by the newly-born mammal is an instinctive action, involving the
use of inborn bodily tools--the diaphragm, lungs, etc. We ought not
to think of the lips and mouth and pharynx of the young baby apart
from the actions of suckling the mammæ of its mother, but usually we
say that this action is an instinctive one. Where does the ordinary
functioning of an organ end and its instinctive functioning begin?
Are the muscular actions of the lobster when it frees its body and
appendages from the carapace during the act of ecdysis instinctive
ones? Most zoologists would say that they are not, any more than the
movements of the maxillipedes in respiration are instinctive ones, yet
they probably would not hesitate to say that the action of the “soft”
lobster in creeping into a rock crevice is instinctive. Does a young
child really “learn” to walk? It is more likely that the actions of
walking are potential in its limbs and that they become actual when all
the connections of nerve tracts and centres in its brain and spinal
cord become established. What is the difference between the acquirement
of the ability to walk and to write? The latter series of actions are
unfamiliar combinations of nervous and muscular activities which are
no part of the organisation of the young child; while the former are
simply the result of the complete functional development of certain
nervous and muscular apparatus.
It seems difficult, then, to express clearly what is the essential
difference between instinctive and intelligent behaviour; and it is
doubtless the case that reasoned experiments and observations are
still too few to enable us to make sound deductions. But it certainly
seems as if we ought to think of instinctive actions as having evolved
concomitantly with the structure of the organs which effect them:
they are those _inheritable adaptations of behaviour_ which are bound
up with--are indeed the same things as--inheritable adaptations
of structure. In performing them the instinctively acting animal
is doubtless aware of its own activity, but we must think of this
awareness as being of much the same nature as our consciousness of the
automatic activities of our own bodies--the rhythmic activities of the
heart and respiratory organs, or the actions of our arms and legs in
walking, for instance. It is knowledge of the inborn ability of the
organisms to use an inborn bodily tool.
In the intelligent action we certainly see something different from
this. The organ or organ-system which carries out such an action
functions in a manner which is different from that for which it was
evolved: the action is the conscious adaptation of the organ for some
form of activity new to it, and this acquirement of activity seems
to be non-inheritable--at least it is non-inheritable in the sense
in which we speak of acquired characters being non-inherited. It is
accompanied, while it is being acquired, by a consciousness which is
deliberative, and is different from that awareness of its own activity
which accompanies the acting of the instinctive animal--the knowledge
that it is acting in an effective manner. It does not seem as if the
animal in so acting is aware of the relation of the bodily tool to the
object on which it is acting. But intelligence seems to imply more than
this: it implies the knowledge of the organism that some parts of its
body bear certain relations to the parts of the environment on which
they are acting, and that these relations are variable ones and may be
the objects of conscious choice.
CHAPTER VIII
THE ORGANIC AND THE INORGANIC
It is convenient that we should express the results of biological
investigation in schemes of classification, for only in this way can
we reduce the apparent chaos of naturally occurring organic things
to order, and state our knowledge in such a way that it can easily
be communicated to others. But we must always remember that the
classifications of systematic biology are conceptual arrangements,
depending for their precise nature on the point of view taken by their
authors. The clear-cut distinctions that apparently separate phylum
from phylum, class from class, order from order, and so on, do not
really exist. There are no such categories of organisms in nature as
genera, families, and the higher groupings. All that we can say exist
naturally are the species, since all the organisms composing each
of these groups are related together by ties of blood-relationship,
and all are isolated from the organisms composing other species by
physiological dissimilarities which render the plants or animals of
one species infertile with those of any other. Such would doubtless
have been the opinion of most botanists and zoologists prior to the
work of de Vries, but we must now recognise that the systematic, or
Linnean, species of the nineteenth century was just as artificial a
category as were the genera and families. Our arrangements of plants
and animals into systematic species and the higher groupings are
therefore convenient ways of symbolising the results of morphological
and physiological investigations, although they also indicate the main
directions taken by the evolutionary process, but the manner in which
they are stated in taxonomic schemes is always a more or less formal
one.
There are no absolute distinctions between group and group, even
between the animals and the plants. There is nothing, for instance, in
the morphology of a Diatom to indicate that it belongs to the vegetable
kingdom, or in that of a Radiolarian, to indicate that it is an animal.
Peridinians are either plants or animals according to the general
argument, or the point of view of the author who writes about them.
Even a study of the energy-transformations that are effected in the
living substance of these lower organisms does not afford an absolute
distinction: synthetic metabolic processes in which energy passes
into the potential condition may be carried out in animals, while
many plants--the saprophytic fungi, or the insectivorous plants, for
instances--may effect analytic energy-transformations of essentially
the same nature as those exhibited in the typical mode of animal
metabolism. Motility and the possession of a sensori-motor system
do not afford the means of making a sharply drawn line of division
between plants and animals. Potential energy passes into the condition
of kinetic energy in the typical animal, and this kinetic energy is
directed by the sensori-motor system. But some lower unicellular
plants are motile, and they possess the rudiments of a sensori-motor
system in the flagella by which their movements are effected. On the
other hand, the sensori-motor system has become vestigial in many
animal parasites--in the Crustacean _Sacculina_, for instance, which
is parasitic on some Crabs. The possession of consciousness, in so
far as we can say that other animals than ourselves possess it, is no
distinction between the two kingdoms of life. Consciousness, judged
by the degree of development of motility, must be supposed to be
absent or very dim in the extreme cases of parasitism attained by some
animals; on the other hand, we may assume that it is present, to some
extent at least, in the highly motile zoospores of the Algæ. Thus some
lower organisms, the Peridinians and the algal spores, exhibit all the
characters which we utilise in separating animals from plants--the
chlorophyllian apparatus, by means of which the kinetic energy of solar
radiation becomes transformed into the potential energy of organic
chemical compounds; the apparatus of receptor and motile organs, by
means of which the potential energy of stored chemical compounds passes
into the kinetic energy of bodily movements; and the existence (so far
as we can say that it exists in organisms other than ourselves) of some
degree of consciousness.
Neither do those morphological schemata which we construct as
diagnostic of phyla, or classes, or orders, etc., separate these groups
from each other so clearly and unequivocally as our classifications
suggest. It might seem for instance that the presence or absence of
a notochord would sharply distinguish between the vertebrate and
invertebrate, but structures which suggest in their development the
true notochordal skeleton of the typical vertebrate animal are to be
traced in animals which exhibit few or none of the characters which
we regard as diagnostic of the Vertebrate. Typical Arthropods and
typical Vertebrates seem to be distinct from each other, but the
extinct Ostracoderms of Silurian times _may_ have been animals which
possessed an internal axial skeleton, and which were also armed
by a heavy dermal exo-skeleton. It is a hypothesis of considerable
plausibility that they really were Arthropods, on the other hand they
are usually regarded as Vertebrates. So also with most other phyla: the
morphological characters which absolutely distinguish between one group
and others are very few indeed, and the small appended groups that lie
about the bases of these larger groups may present one or other of the
characters of several phyla. Looking at the morphology of the animal
kingdom in a general kind of way, one does indeed see that a certain
structural plan is characteristic of the organisms belonging to each
of the great phyla, while more detailed structural plans may be said
to be characteristic of the sub-groups. But minute morphological and
embryological investigation reduces almost to nothing the characters
which are absolutely diagnostic of these various groups.
No more than the nature of the energy-transformations, and the
essential morphology, does the behaviour of animals afford us the
means of setting up absolute distinctions between group and group.
Really tropistic behaviour is exhibited by the movements of the stems,
roots, and leaves of green plants, or in the movements of Bacteria,
and perhaps some unicellular animals. Typically instinctive behaviour
is exhibited by the individuals of societies of Insects and by many
solitary-living animals belonging to this class; and typically
intelligent behaviour is exhibited by the acting of the higher
Mammalia. Yet there is undoubtedly much that is truly instinctive
in the behaviour of Man, and something of the same nature as his
intelligence seems to inhere in the instinctively-acting mammal
or insect: how else could an instinctive action become capable of
improvement? We cannot doubt that intelligence is manifested by
a dog or by much that we see in the behaviour of ants. No rigid
distinctions between tropisms, such as we have mentioned above, and
the reflexes that may be taken to constitute instinctive behaviour,
can be established. Minute analysis, such as that carried out by
Jennings on the swimming movements of the Protozoa, leaves us quite
in doubt as to how these modes of behaviour are most properly to be
described; and all the controversy as to the nature of tropisms,
reflexes, instinct, and intelligence surely indicates that these modes
of behaviour have something that is common to all of them, and that
no clear and certain distinction can be said to separate one from the
other. Even those psychic processes which we call intellectual do not
seem to be different in kind from some that we attribute to the lower
animals: the Protozoan _Paramœcium_ studied by Jennings, or the crabs,
crayfishes, and starfishes studied by Yerkes and others really _learn_
to perform actions, but this learning is said to be the result of a
process of “trial and error.” The animal tries one series of movements
and finds that it fails, tries another and another with a similar
result, and in the end finds one that is effective. This is remembered,
and when the same problem again confronts the animal it is solved
after fewer trials, and finally, after experience, the end-result is
attained at once without previous trials. Now many of what we call
truly intellectual processes are certainly processes of precisely this
nature. Hypothesis after hypothesis _occurs_ to the scientific man (or
to the detective, or to the engineer confronted with some exceptional
difficulty), and one after another is tested by actual trial, or by a
process of reasoning (which is really the rapid and formal resuming of
previous experience), until a hypothesis verifiable, or _a priori_
verifiable, is found. What, for instance, are our mathematical methods
of integrating a function, or working a long division sum, but methods
of scientific “guessing,” and verification of the hypotheses so made?
They are truly instances of the method of trial and error practised by
the lower animals.
All the above amounts to saying that there is a community of energetic
processes, of morphology, and of behaviour in animals and plants.
“Protoplasm” is the same, or much the same chemical aggregate, whether
it is contained in the cells of animals or plants. The cell, with
its nucleus, chromatic architecture, cell-inclusions, and cell-wall,
is essentially the same structure in all organisms. The complex and
specialised process of nuclear division in tissue growth, or the
series of events which constitute the acts of fertilisation of the
ovum or its plant correlative, are the same all through the organic
world. The sensori-motor system--receptor organ, nerve-fibre and
cell, and effector-motor organ--is the same all through the animal
kingdom. Alimentary canal and glands, enzymes, excretory tubules,
contractile blood-vascular apparatus--all these are structures which
are functionally the same, which are built on essentially the same
morphological plan. Life, whether it is the life of plant or animal,
makes use of the same material means of perpetuating itself on the
earth and avoiding the descent of matter towards complete inertia.
Absolute dissimilarities, dissimilarities such as those between atoms
of hydrogen and oxygen, or between a point and a straight line, or
between rest and motion, do not exist between the different categories
of entities that make up the organic world. Yet differences do exist,
and must we conclude that because these differences are not absolute
ones, because they are differences of degree, and not of kind, they
are not essential, are not differences at all? Must we say, for
instance, that although an animal is a much more efficient machine
than a gas-engine (in the sense of efficiency as understood by the
engineer), there is really no difference between them, that they are
both thermo-dynamic mechanisms, since in both energy is dissipated?
Ought we to say that, because the last steps in the formation of urea
in the animal body are synthetic ones, there is really no difference
between the nature of the energy-transformations that occur in the
animal and the plant modes of metabolism? Ought we to say that,
because a dog may sometimes act intelligently and a man instinctively,
psychically they are similarly-behaving organisms? Surely this amounts
to saying that, because things are not absolutely different, they are
the same; and surely the mode of reasoning is a vicious one!
What we clearly see in the different kinds of organisms--in
the metabolically constructive plant and the metabolically
destructive animal; or in the instinctively-acting Arthropod and
the intelligently-acting Mammal--is the progressive development of
different _tendencies_. If the green plant is, in its essence, the
same kind of physico-chemical constellation as is the animal, yet the
tendency of its evolution has been that more and more it has acquired
the habit, or the power, of using solar radiation to combine together
carbon dioxide, water, and nitrogenous inorganic salts to form proteid
and carbohydrate substances. On the other hand, the tendency of the
animal has been more and more to absorb into its own tissues the
proteid and carbohydrates synthesised by the green plant, and then to
break these substances down into carbon dioxide and water, and less and
less to effect such syntheses as are effected by the plant. Even if
the Annelid worm, the Arthropod, and the Vertebrate were, at the origin
of their ancestries, animals which were very like each other in the
morphological sense; even if there are some Arthropods which are very
like Annelids, and some Annelids which might very easily be imagined
to become transformed into Vertebrates, and some extinct Arthropods
which may after all have been Vertebrates, yet it is the case that the
tendencies of the evolution of each of these groups have been very
different. All the while the Vertebrate tended more and more to develop
a rigid axial rod or notochord, becoming later a jointed vertebral
column, and a soft, pliable, exo-skeleton; while the Arthropod tended
more and more to develop a rigid exo-skeleton, and to remain soft in
its axial parts. Even if these two tendencies may not have been fully
realised, is it not the case that they are really different things?
The evolutionary process has therefore been, in its essence, the
development, or unfolding, of tendencies originally one.
What is the evolutionary process? It is usually regarded as a progress
from organic simplicity towards organic complexity. Yet if we think
about it as a physical process we cannot say that any one stage is
any more simple or complex than any other stage. Let us compare
organic evolution with the process of inorganic evolution, as, of
course, we are compelled to do if we regard the former process as a
physico-chemical one. Assume, then, that the nebular hypothesis of Kant
and Laplace is true--it will make no difference to our argument even if
this hypothesis is not true, and it is more easily understood than any
other hypothesis of planetary evolution. Originally all the materials
composing our solar system existed in the form of a gaseous nebula
possessing a slow rotatory motion of its own. It does not matter that
the silicates, carbonates, oxides, and all other mineral substances
that we now know existed then in the form of chemical elements, or the
precursors of chemical elements: all the material bodies now present
in the solar system were present in the original nebula. The energy
of this nebula consisted of the potential energy represented by the
separation of atoms which later on became combined together, and of the
kinetic energy of motion of these atoms; and this material and energy,
together with the other cosmic bodies radiating energy to it and
those bodies receiving the energy which it lost by its own radiation,
constituted a system, in the sense of the term as it is employed by the
physicists. Now, in the process of cosmic evolution this system became
transformed, because it was continually losing energy by radiation. As
it cooled, the mean free paths of its atoms and molecules became less
and less, and finally condensation to the liquid and then to the solid
condition occurred. The parts of the nebula continually gravitated
together, so that it became smaller and smaller while its rotatory
motion became greater. Finally, mechanical strains became set up in
its mass as the consequence of the increased velocity of rotation, and
disruption occurred with the formation of the sun, the planets, and
the satellites. There was no increase of complexity of the system. At
any moment of time its elements, that is, the chemical atoms composing
it and the energy of these atoms, was the same as at any other moment
of time. Heat-energy may have been radiated from one part of the
system--the heated nebula--to some other part of the system--the other
cosmic bodies absorbing this radiation, but the total energy of the
system remained the same. The chemical atoms may have combined together
to form molecules and compounds, and their energy of position may
have become the energy of motion, but the ultimate materials were
still the same. What happened during the cooling and contraction of
the nebula was a rearrangement of the elements of the system, that is,
of the atoms and their energies. At any moment of time the condition
of the system was an inevitable consequence of the condition at the
moment immediately preceding this, and a strict functionality, in the
mathematical sense, existed between the two conditions. It was not
more complex in the later stage than in the earlier one--it was merely
different. Stages of evolution were really _phases_ in a transforming
system of matter and energies.
If we choose to regard organic evolution as a similar process of
physico-chemical transformation, we must also regard the totality of
life on our earth, with all the inorganic materials which interact with
organic things, and with all the energies, cosmic and terrestrial,
which also so interact, as a system in the physical sense. We are
now compelled to think about this system in the same way as we
thought about the cosmic one, that is, we must postulate that a rigid
mathematical functionality existed between any two conditions of it,
and that the latter condition was inevitably determined by the former
one. We must think of the system as at all times composed of the same
elements. In its later condition life may have been manifested in a
greater mass of material substance than in its earlier conditions, but
this increase of mass was only the increase of one part of the system
at the expense of another part. At all times, then, the constitution
of the system was the same, and different stages of the evolutionary
process have only been different phases, or arrangements, of the same
elements. At no time was the organic world any more or less complex
than at any other time. In its “primitive” condition _all was given_.
Mechanistic biology does not, of course, hesitate to accept this view
of the evolutionary process. The “Laplacian mind” must have been able
to calculate what would be the condition of the system at any phase,
knowing the positions of all the atoms or molecules in the original
nebula, and the velocities and directions of motions of all these atoms
or molecules. Just as (in Huxley’s illustration) a physicist is able to
calculate what will be the fate of a man’s breath on a frosty day, so
the Laplacian mind must have been able to predict the fauna and flora
of the world in the year 1913 from a complete knowledge of the material
nature and energetic properties of the nebula from which it arose.
We cannot fail to see, on reflection, to what this view of the nature
of the evolutionary process leads us. The primitive world-nebula was a
system of parts which had extension in space. Materially it consisted
of atoms isolated from each other by space, and energetically it
consisted of the movements of these atoms, and of the energy of their
positions with regard to each other. No two atoms could occupy the
same space--they mutually excluded each other: this is what we mean by
saying that the original--and every other--state of the system was a
state of material things or elements spatially extended. Therefore, if
the physical analogy is consistently to be retained, the organic system
undergoing evolution was a system of elements which at any moment
whatever were spatially extended. It was really a system of atoms or
molecules possessing kinetic energy of motion, or potential energy of
position--molecules which lay outside each other, and energies which
were really the movements or positions of these molecules, and which
therefore lay outside each other in the same sense.
The evolution of the individual organism must be a process of the
same kind. Like cosmic and phylogenetic evolution, it is apparently
a progress from the simple to the complex. A minute fragment of
protoplasmic matter, homogeneous in composition, or apparently so,
grows and differentiates, becoming the complex structure of the adult
organism. Here the system in the physical sense is the fertilised ovum,
the oxygen and nutritive matter which have become incorporated with
it, and the physical environment with which these things interact. All
these elements existed in that phase of the system which contained
among its parts the fertilised ovum, as well as in that phase which
contained the fully developed organism. Complex by comparison with
the fertilised ovum and its environment as the adult animal and its
environment may seem to be, it is only a different phase of the same
system. Further, all the parts that form the tissues of the adult, and
all their motions, are spatially extended, and are only rearrangements
of the molecules and of the motions of the molecules that were actually
present in the system in its initial phase. Speculation along these
lines has led to all the results of Weismannism. All the parts of
the adult organism are really present in the fertilised ovum and the
nutritive matter which is to build up the fully developed animal, not
in potentiality it must be noted, but actually present in the spatially
extended condition. It is true that the hypothesis only requires that
the determinants of the adult organs and tissues, and of the adult
qualities, should be present in the ovum; but since the energies
necessary for the separation of these determinants, and for their
arrangement and growth in mass, must also be present in the initial
phase of the system, it is evident that the hypothesis implies that
all the material structure of the animal is present in the spatially
extended form in the initial phase of the system. Just as the adult
animal is a manifoldness of material parts and energies that possess
extension, so also is the undifferentiated embryo and its material
environment an extensive manifoldness. We cannot otherwise conceive
it if we are to retain the mechanistic view of the development of the
individual organism.
Let us think of the process of organic evolution in another way by
comparing it with the mathematical process by which we form the
permutations and combinations of a number of different things.
Individual development is termed the assumption of a mosaic structure,
that is, all the parts of the adult are assumed to be present in
the embryo, but in a sort of “jumbled-up” condition. As development
proceeds, these parts become sorted out and arranged in a pattern which
continually becomes more and more distinct. Much the same process
of arrangement and segregation must be assumed to have occurred
during the process of racial evolution: the parts of the “primitive”
life-substance, with all the parts of the physical environment which
become incorporated with it during its evolution, must have become
segregated and arranged so as to form the existing species of plants
and animals. A permutation, then, of the separate things _a_, _b_,
_c_--_x_, _y_, _z_, is an arrangement of all these things: obviously
there are a very great number of ways in which the letters of the
alphabet may be arranged, 26! in all. But we may take some
of the letters and arrange them in different ways: the selections _a_,
_b_, _c_, _d_, can be arranged in 4! ways _b_, _c_, _d_, _e_, also in
4! ways, and so on. Thus by a process of dissociation and arrangement
of a certain number of elements, a very great number of different
things--things which consist of elements spatially extended--can be
obtained.
The group of things, _a_, _b_, _c_, _d_--_x_, _y_, _z_, was an
extensive manifoldness, since it was formed by juxtaposing in space the
separate units of which it is composed. Yet it is an unitary thing, for
it is a different thing from the group, _b_, _c_, _a_--_x_, _y_, _z_.
It is also a multiplicity, for it can be transformed into every one of
the 26! permutations, and broken up into the selections of some of the
separate things of which it is composed, and of the permutations of the
things taken in each of these selections. In a way these arrangements
exist in the group _a_, _b_, _c_--_x_, _y_, _z_, and yet the group
itself possesses no other actual extended existence than the group of
things that it is. It is an _intensive multiplicity or manifoldness_
in that the potentiality of all the arrangements exists in it but not
in the spatially extended condition. It is a multiplicity only when we
associate with it the mental operations by which we conceive of its
dissociation and rearrangement. By reason of these mental operations
the intensive multiplicity of the group becomes the extensive
multiplicity of its arrangements.
This appears to be the only really philosophical way in which we can
attempt to picture to ourselves the processes of individual and racial
evolution. The “primitive” life-substance, or the undifferentiated
ovum, each of them with its environment, was an intensive manifoldness,
a multiplicity of distinct things or qualities which co-existed, and
which were not separate each from other in that they occupied different
compartments of space, but which interpenetrated each other. This
notion of distinct things co-existing in time, yet occupying the same
space, is not at all a difficult one. Our consciousness is such a
multiplicity of states or qualities all in one. The idea of a group
of figures has a very real existence for the sculptor, and he may
visualise it with almost all the appearance of reality that the actual,
material piece of statuary possesses. In his mind it is a real manifold
existence, which nevertheless does not occupy the three-dimensional
space which the marble fills. The musical notes C, F, A, C, heard
in arpeggio, are things which possess real existence, but which are
extended in time, and when we think of these separate sounds we lay
them alongside each other in our mind in an empty, homogeneous medium
which seems to be all that we think of as space. Yet the same notes
heard simultaneously as a chord are not extended. They interpenetrate
each other, but yet they are distinct things, since on hearing the
chord we can recognise the notes composing it. As an arpeggio the notes
are an extensive manifoldness, but as a chord they are an intensive
manifoldness.
The mechanistic biology of the latter part of the nineteenth century
based itself on the methods and concepts of physics, and it was
therefore compelled to assume that the manifoldness of the “primitive”
life-substance--the “Biophoridæ” of Weismann and his followers--or that
of the fertilised ovum, was a manifoldness that had spatial extension.
All the systems studied by physics were aggregates of elements, or
parts, that had such extension: the sun, with its attendant planets and
satellites, was a system of bodies isolated from each other in space.
Even the atmosphere, or the sea, media which to our unaided senses
appear to be homogeneous, are really media consisting of discrete
bodies, or molecules, which are not actually in contact with each
other, but which are separated from each other by empty space. Chemical
compounds were assemblages of molecules, molecules were assemblages of
atoms, and the atoms themselves were either simple or were composed of
corpuscles, or still smaller bodies. This mode of analysis was forced
upon the human mind by formal logic and geometry, and it was apparently
the only method of acquiring mastery over nature. Yet there were
difficulties, appreciated no less by the philosophical physicists than
by the writers on formal philosophy. How could bodies, or molecules,
or atoms that were separated from each other act upon each other?
The molecule A could only act upon the molecule B if there were some
particles between them which could convey the impulse or attraction,
but then we must suppose that there were other particles between these
intermediate ones, and so on _ad infinitum_, otherwise how could a
body act, that is, really exist, where it was not? In other words,
how could there be action at a distance? How, for instance, could the
atoms of the earth attract those of the moon with a force sufficient
to break a steel rope of 400 miles in diameter? Physics had therefore
to invent the ether of space, not only to account for interstellar
or interplanetary gravitation and other modes of radiant energy, but
also to account for the interaction of the atoms or molecules which
make up chemical compounds. In our own day atoms have ceased to be the
limits to the subdivision of things: they are composed of electrons,
but the electrons are entities separated from each other by empty
space. They are not, however, the ultimate limits of subdivision of
matter, as the atoms were supposed to be by the chemistry of the early
part of the last century, but are regarded as “singularities” in an
universal continuous medium or ether. It is of no moment that we are
unable to describe the ether in terms of our former concepts of matter
and energy, or at least that we can only so describe it in such a
way that it is represented by negative qualities: we are compelled to
postulate its existence in order to avoid philosophical confusion. The
universe is therefore a continuum, and an atom or any other body exists
wherever it can act. The atoms of a fixed star, so far away that we
can only represent its distance in billions of miles, are nevertheless
on our earth as well as at the point of space which we regard as their
astronomical position, for the light emitted by them acts on our
retinas. The universe is an unitary thing in that it is a continuous
medium or substance in the philosophic sense, but it is also a
multiplicity in that singularities or conditions of this medium pervade
each other throughout space. Such seem to be the conclusions towards
which the later physics forces us, and it is interesting to reflect how
different biological speculation might have been had it been formulated
now instead of half a century ago!
Why has a process of evolution occurred at all? Why is it that
tendencies that might have co-existed, that indeed do co-exist to
some extent, have become separate from each other? It is possible
to conceive of an organism which contains chlorophyll, and which
might therefore synthesise carbohydrate and proteid from inorganic
substances, but which might also contain a sensori-motor system, and
which might therefore expend the energy so obtained in regulated
movements. To a certain extent such organisms combining the plant
and animal modes of metabolism do exist among the Protista. Yet, the
effect of the evolutionary process has been more and more to dissociate
the plant and animal modes of metabolism until the typical animal is
quite unable to make use of carbon dioxide and water as materials to
be synthesised, while the typical plant has lost all power of motion
except the tropistic movements of its roots, leaves, and stems.
Instinctive and intelligent behaviour coexist in many animals, yet
the tendency of man, most highly intelligent of all, is more and more
to act intellectually; while the opposing tendency, that is, to act
instinctively, has been evolved in the Hymenoptera. It seems as if
such contrasting methods of transforming energy, or of acting, were
incompatible with each other, and yet it is clear that they are not
really incompatible, for they may co-exist. But it does seem clear
that each of these contrasting tendencies cannot be manifested to the
fullest extent if it is accompanied by the other. That is to say,
life is limited in its power over inert matter. Manifested in the
same material constellation, it cannot both use solar radiation to
build up substances of high potential energy and then break down these
substances so as to obtain kinetic energy of movement. Now we see
clearly that life on our earth is indeed limited to a very restricted
range of physical conditions. When we think of the mass of the earth we
are surprised to find what an insignificant fraction of all this matter
displays vital phenomena. The surface of the land is clothed with a
layer of vegetation, luxuriant and abundant as we see it when we walk
through a tropical forest, but which is really a film of inconceivable
tenuity when we compare its thickness with the diameter of the globe.
Even the whole surface of the land is not so clothed with vegetation,
for polar regions and the tops of high mountains are almost lifeless,
while desert tracts may be absolutely so. The lower strata of the
atmosphere are inhabited by birds, insects, and bacteria, but the total
mass of these is infinitesimal when compared with the total mass of
the gases of which the atmosphere is composed. Even the sea, which we
regard as rich in life, is not really so: estimates of the luxuriance
of planktonic life are really misleading, for although a single drop
of water may contain some hundreds of organisms, the mass of these is
exceedingly small and is usually expressed as one or two parts per
million. All this means that life has difficulty in manifesting itself
in material forms. Whether it be simply a mode of interaction of some
complex chemical substances with a relatively simple physico-chemical
environment--the mechanistic view--or whether it be an impetus or
agency which is neither physical nor chemical, but which acts through
physical and chemical elements--the vitalistic view,--life is capable
of acting on terrestrial materials to a very limited extent. Acting
through all the tendencies which we see to exist in it, life may be, so
to speak, diluted; but by being concentrated in one or a few of them it
becomes more effective. The dissociation of this bundle of tendencies
which we call life is therefore the meaning of the evolutionary process.
Ontogenetic development, says Roux, is the production of a _visible_
manifoldness. It cannot be said that this cautious description of the
developmental process has been apprehended by those who expound the
dogmas of mechanistic biology. Development is indeed the production
of a diversity, but this diversity is only a phase of a preceding
diversity, a rearrangement of spatially extended pre-existing elements.
How else could the developing embryo and its material environment be
regarded as a system of physico-chemical elements, capable of study
by the methods of experimental and mathematical physics, except by
regarding it as a system passing through phases each of which is a
necessary consequence of the preceding one, and each of which contained
the same elements separated from each other in space? Let us think
of water occupying a vessel at a high temperature and continually
cooling. The states of this system are (1) the gaseous state in
which the molecules of the water are moving at a high velocity and
are a relatively considerable distance apart, and in which they are
incessantly colliding with each other and with the walls of the vessel;
(2) the state of the system consisting of the separate phases, liquid
water and gaseous steam in contact with it; and (3) the solid phase, in
which the molecular motions almost, or quite, cease. Here the progress
of the system through its phases leads to physical diversity and then
again to physical homogeneity. But the diversity of the different
phases is in a sense an apparent one only: any single phase, or at
least those which involve the passage of the system from the gaseous
to the liquid phases, and _vice versa_, can be represented by van der
Waal’s general equation, RT = (_p_ + _a_/_v_^2) (_v_ - _b_). Does
anything in modern biological investigation, except, of course, the
speculations of non-physical physiologists, suggest that an ontogenetic
process can be represented in such a manner?
Are the arbitrary “stages” of the embryologists--the ovum, blastula,
gastrula, etc., phases in a system in the above sense, the only sense
in which the process can be regarded as capable of physico-chemical
analysis? What precisely is the embryo at the close of the process of
segmentation? It is an harmonious equipotential system, that is to say,
an assemblage of discrete organic parts or cells, each of which has all
the potentialities that every one of the others has. _Any_ cell in the
blastula may become a cell, or a series of such, in _any_ part of the
gastrula or pluteus larva. This is what the parts are in potentiality,
but actually their individual fates are different. The system is an
harmonious one, and each of its parts, although able to do whatever
any other part can do, yet does one thing only: it becomes an endoderm
cell, or an ectodermal cell, or a part of the skeleton, and so on; what
it does depends on its position with regard to the other cells. An
extensive manifoldness or diversity is produced, but this was not the
consequence of a preceding extensive manifoldness, for in the preceding
stage _all the parts of the system were the same_. The manifoldness of
the ovum or blastula--that potential manifoldness which became actual
in development--must be an intensive manifoldness, and admitting this
we must abandon the comparison of the ontogenetic (and, of course,
phylogenetic) processes with the phases of a physico-chemical system
in process of transformation. _Evolution is the transformation of an
intensive into an extensive manifoldness._
More than this--much more than this--must be the difference between the
transforming systems of physics and the evolving systems of biology.
There is a quality, or sense, or direction in all naturally occurring
inorganic processes which is not like that of organic evolutionary
processes. We return now to the consideration of the second law of
thermodynamics, for only in this way can we approach the notion of
the vital impetus. If an energy-transformation occurs in inorganic
nature, that is to say, if anything happens, the transformation occurs
or the thing happens because there were diversities in the system in
which it occurred. The condition for inorganic happening is that there
must have been differences of energy in the different parts of the
system: in the most general sense there must have been diversity of
the elements. But with the transformation this diversity disappears,
or tends to disappear, and it cannot be restored--that is, differences
of energy cannot again be established unless by a compensatory
energy-transformation; that is, energy must be expended on the system
from without by some external agency. Whatever else physics shows
us it shows us an unitary universe, that is, an universe in which
anything that happens affects, to some extent, all the other parts.
Therefore the diminution of diversities, or energy-differences, is
something that cannot be undone, or compensated, for there is nothing
without the universe.[32] Everything that happens in our universe
reduces the possibility of further happening. We desire, at the risk
of reiteration, that this principle of energetics should be perfectly
clear: inorganic happening, of whatever kind it may be, is a case or
consequence of the second law of energetics--_is_ the second law itself
in a sense. All energy-transformations occur because energy-differences
are being diminished, because diversities are being abolished. This is
the sense, or quality, or direction of inorganic phenomena.
[32] It is assumed that the universe is a finite one. If it were
infinite the whole discussion becomes meaningless, and we must _give
up_ this and other problems.
It is not the direction of organic evolution. In the development of
the individual organism what we most clearly see is the progressive
increase of diversity of the parts. In phylogenetic evolution one,
or a few, simple morphological forms of life have become, and are
becoming, indefinitely numerous morphological forms. Diversity is
continually increasing. If we cling to the mechanistic view of life,
we must suppose that the diversity of the fully developed organism, or
that of the organic world with all its species, was also the diversity
of the fertilised ovum or that of the primitive life-substance in
another phase. Then we commit ourselves to all the crudities of modern
speculations on heredity.
With this increasing diversity of form there is a concomitant
segregation of energy. We see as clearly as possible that the tendency
of all inorganic happening is the transformation of potential into
kinetic energy, and the equal distribution of this kinetic energy
throughout all the parts of the system in which the happening
occurred. On the other hand, the tendency of organic happening is the
transformation of kinetic energy into potential energy, (1) in the
stores of chemical compounds which result from the metabolism of the
green plants, and which are capable of yielding energy again; and (2)
in the results of the instinctive or intelligent activities of the
animal’s organism. The first result of organic evolution is clearly
to be traced and needs no further explanation, the second is apparent
on reflection, but is perhaps not clearly apprehended in all its
significance by the student of biology and physics.
Organic evolution is the process which has had, or is having, for its
tendency the development of the putrefactive and fermentation bacteria,
the chlorophyllian organisms, the Arthropods, and man and other
mammals. All that we have said has been futile if this teleological
description of the evolutionary process has not been clearly suggested.
The indefinitely numerous forms of life that have appeared on the
earth in the past, and are now appearing, seem to be experiments most
of which have been unsuccessful. Only in the organisms mentioned,
organisms which are complementary in their metabolic activities,
has life been successful in manifesting itself in activities which
are compensatory to those of inorganic nature. The energy which is
dissipated in the radiation of the cooling sun is again made potential
in the form of the carbohydrates, synthesised from water and carbon
dioxide by the agency of the chlorophyllian organisms, and this energy
accumulates. It is employed by the instinctive and intelligent animal,
in that it is used as food and converted into bodily energy, which can
then be utilised for any purpose that is contemplated. These plant
substances taken in by the animal as sources of energy are broken
down into excretory substances, which are further broken down by the
metabolic activity of the fermentation and putrefaction bacteria, and
become the substances used as foods by the chlorophyllian organisms.
If the activities of man were only those of undirected or misapplied
muscular movements (as indeed most of his activities have so far been),
then cosmic energy would truly be dissipated after it had become the
energy of organisms. But does not all the history of man point to his
ever-increasing activity in the conquest over nature, that is, the
effort to hoard and employ natural sources of energy, and to arrest its
tendency towards dissipation?
It must be admitted that the past history of human civilisation
has been almost entirely that of the irresponsible exploitation of
natural resources--for it has been founded on the thoughtless and
wasteful utilisation of energy which was made potential by the plant
and animal organisms of the past. Man, the hunter, maintained himself
and multiplied by the destruction of other animals or plants, or by
the mere collection and utilisation of naturally occurring fruits and
other plant-substances. During historic times the bison and other
animals have almost become extinct owing to his ruthless activity,
just as in our own days the whale, sole, and turbot are disappearing
before the activity of the machine-aided fisherman. Industrial man has
been successful with his factories and railroads and steamships, and
his electrical power and transport, only because he has been able to
utilise the stores of energy contained in the coal and oil accumulated
in the rocks of the earth. The progress of civilisation has been a
progress rendered possible by discovery and invention, and by the
application of the knowledge so obtained to the practical things of
human life, but in this speculation and its application two different
things are indicated. For the scientific man and the philosopher the
reduction of the apparent chaos of nature to law and regularity is
the beginning and end of his mental activity; but the object of the
“entrepreneur” or “organiser” or the “captain of industry” has been
to employ these results of thought to the irresponsible exploitation
and the selfish depletion of natural sources of energy. Just as the
bison and other animals have disappeared or are disappearing before the
hunter and fisherman, so the stores of coal and oil are disappearing
before the activities of commerce. It has been said that the triumphs
of industrialism are only the triumphs of the scientific childhood
of our race. Human effort has so far only contributed to the general
dissipation of natural energy.
Yet just as man, the hunter, has been succeeded by man, the
agriculturalist, so this irresponsible depletion of natural wealth
must be succeeded by the endeavour to retard, and not to accelerate,
the degradation of energy. Plants and animals which were simply killed
by primitive man are now sown and harvested, or cultivated and bred;
so that the energy of solar radiation, which formerly ran to waste,
so to speak, is now being fixed by the metabolic activity of the
green plants of our crops and harvests. Rainfall and winds, tides and
rivers, all represent energy primarily derived from solar radiation
and from the orbital and rotatory motions of the earth and moon. This
energy even now is almost entirely dissipated as waste, irrecoverable,
low-temperature heat; but more and more as our stores of coal and
oil are being depleted, the attention of men is being directed to
these sources of kinetic energy. Waterwheels and windmills, and the
more effective mechanisms that must be evolved from these primitive
motors, will capture this waste energy and convert it into the kinetic
energy of machines serviceable to man, or into the potential energy of
chemical compounds capable of storage and future utilisation. The study
of radio-activity has made us acquainted with the enormous stores of
potential energy locked up in the atoms, and if it ever should become
possible to utilise this by the disintegration of these particles, the
downward trend of natural energetic processes will further be retarded.
Life, when we regard it from the point of view of energetics, appears
therefore as a tendency which is opposed to that which we see to be
characteristic of inorganic processes. The direction of the latter
is towards the conversion of potential into kinetic energy, and the
equal distribution of the latter throughout all the parts of the
universe. The direction of the tendency which we call life is towards
the conversion of kinetic into potential energy, or towards the
establishment and maintenance of differences of kinetic energy, whereby
the latter remains available for the performance of work. In general
terms, the effect of the movement which we call inorganic is towards
the abolition of diversities, while that which we call life is towards
the maintenance of diversities. They are movements which are opposite
in their direction.
What is cosmic evolution? In all the hypotheses which astronomical
physics has imagined we see the transformation of a system--a part of
the universe arbitrarily detached from all the rest--through a series
of stages, each phase of the series being marked by a progressive
decrease of diversity, that is, by some degradation of energy. Two
main series of hypotheses accounting for the present condition of the
universe seem to have been the result of physical investigation: (1)
the origin of discrete solar and planetary bodies by a process of
condensation of a gaseous nebular substance; and (2) the origin of
the same systems by aggregations of meteoric dust. Plausible as is
the nebular hypothesis on first consideration, it fails when it is
subjected to minute analysis. What is a gaseous nebula? It is a mass
of heated vapour contracting by the mutual gravity of its parts as its
molecules lose their heat by radiation--so the hypothesis states. But
it has been pointed out that we cannot be certain that the gaseous
nebulæ known to astronomy are hot, or even that they gravitate. The
great nebula in Orion, it is stated, is at an enormous distance from
us, and making a minimal estimate of this distance the volume of the
nebula must still be incredibly great. There are good reasons for
believing that the mass of the visible universe cannot be greater than
that of a thousand million of suns such as our own. Assuming that all
this matter is contained in the great nebula in Orion (and obviously
only a small portion of it can be so contained), we find on calculation
that the “gas” so formed would be much less dense than even the trace
of gas contained in a high vacuum artificially produced.[33] How, then,
can we speak of such a body as this nebula as an extended mass of hot
gas, cooling and gravitating as it loses heat?
[33] Its density would be 1/(58 × 10^8)th that of our atmosphere.
Even on the other hypotheses, those of the formation of discrete
suns and planets by the aggregation of meteoric dust, and the
compensatory dispersal of such dust by radiation pressure, apparently
insurmountable difficulties arise. All such hypotheses as we have
indicated assume material substance and modes of energy-transformation
similar to those that we study in laboratory processes, and all such
hypotheses involve the notion of the degradation of energy. So long as
we suppose that all cosmic processes are transformations of extended
systems of material substances we must assume that energy is dissipated
at every stage of the transformation, and whenever we assume this we
admit that the processes are irreversible ones, and that the material
universe as a whole tends towards a condition of inertia. Yet this,
we see, cannot be true, for the universe teems with diversity. Is the
progress towards the ultimate state of inertia an asymptotic one, as
Ward suggests? This does not help us, since all that the suggestion
does is to misapply a mathematical device of service only in the
treatment of the problems for which it was developed. Somewhere or
other, it has been said, the second law of thermodynamics _must_ be
evaded in our universe.
How can it be evaded? That movement or progress which we call inorganic
is a movement of energy-transformations in one direction--towards their
cessation. It is a movement which we can easily reverse in imagination.
A cigarette consumed by a smoker represents the downfall of energy:
the cellulose and oils of the tobacco burn with the liberation of
heat, and the formation of water, carbon dioxide, and some soot; and
this is what happens when potential energy contained in an organised
substance becomes converted into kinetic energy. Now, the opposite
process can clearly be conceived--it can even be pictured. If we make a
kinematographic record of the smoking of the cigarette and then reverse
the direction of motion of the film, we shall see the particles of
soot recombining to form the substance of the cigarette, and we can
imagine the concomitant combination of the water, carbon dioxide, and
other substances formed during the combustion with the absorption of
kinetic energy. This is not a mere analogy, for the same reversal of
ordinary chemical happening occurs whenever a green plant builds up
starch from the water and carbon dioxide of the atmosphere and it
also occurs whenever a chemical synthesis of an “organic” compound,
like that of urea by Wöhler, or that of the sugars by Fischer, is
brought about in the laboratory. In all such syntheses the experimenter
_reverses_ the direction of inorganic chemical happening. He may
cause endothermic chemical reactions, reactions accompanied by the
absorption of available energy, to take place, and in these kinetic
energy becomes transformed into potential energy. All the syntheses of
organic compounds so complacently instanced by mechanistic biologists
and chemists as indicative of the lack of distinction between the
organic and the inorganic point to no such conclusion. Sugar is built
up in the cells of the green plant from the inorganic compounds,
water, and carbon dioxide, and is therefore a compound prepared by
life--that of the plant organism. But sugar may also be built up in
the laboratory from inorganic compounds, which may further have been
synthesised by the chemist from their elements. Does this destroy the
distinction between compounds formed by the agency of the organism and
those formed by inorganic agencies? Obviously it does not, for in the
green plant the sugar was formed as the result of the vital agency of
the living chlorophyllian cell, while in the laboratory it was built
up because of the intelligence of the experimenter. Apart from this
intelligence or vital agency, the series of chemical transformations
beginning with the elements carbon, oxygen, and hydrogen, and ending
with the substance sugar, would not have occurred. We have no right to
say, therefore, that such syntheses destroy the distinction between the
organic and the inorganic. What they do indicate is the distinction
between the tendency expressed by the second law of thermo-dynamics
(inorganic processes), and those that occur as the result of direction
conferred upon processes taken as a whole, either by the vital agency
of the living cell, or by the intelligence of man (vital processes).
The direction, therefore, that may be conferred on a series of
physico-chemical processes is what we must understand by the “vital
impetus” of Bergson, or the “entelechy” of Driesch.
It must be admitted that it is difficult to describe more precisely
than we have done above what is meant by these terms. It is with very
much the same embarrassment that is experienced by the physicist
when he has to apply the concepts of mass and inertia, in their
eighteenth-century meaning, to his description of an universe in terms
of electro-magnetic theory, that we seek to describe the modern concept
of entelechy. Yet the physicist has had to make this step forward,
and the same adventure awaits the biologist if the speculative side
of his science is to make further progress, and if he is disinclined
to make his science an appendage of physics and chemistry. Entelechy
does not correspond to the eighteenth-century notion of a “vital
force,” or to the “soul” of Descartes, as the writer of a book on
evolutionary biology seems to suggest. It is a concept which is forced
upon us mainly because of the failure of mechanistic hypotheses of the
organism. If our physical analysis of the behaviour of the developing
embryo, or the evolving race or stock, or the activities of the
organism in the midst of an ever-changing environment, or even the
reactions of the functioning gland, fail, then we seem to be forced
to postulate an elemental agency in nature manifesting itself in the
phenomena of the organism, but not in those of inorganic nature. This
argument _per ignorantium_ possesses little force to many minds: it
makes little appeal to the thinker, or the critic, or the general
reader, but it is almost impossible to over-estimate the appeal which
it makes to the investigator, as his experience of the phenomena of the
organism increases, and as he feels more and more the difficulty of
describing in terms of the concepts of physics the activities of the
living animal.
We may, however, attempt to illustrate mainly by analogy what is
meant by Driesch’s _entelechia_, a more precise concept than is
Bergson’s _élan vital_. We return to the consideration of the behaviour
of the embryo at the close of the process of segmentation. The
organism at this stage consists of a number of cells organically in
continuity with each other, either by actual protoplasmic filaments
or by the apposition of parts of their surfaces, thus constituting
“semi-permeable” membranes. These cells are all similar to each
other, both structurally and functionally. It does not matter that
modern speculations on heredity describe them as unlike in that each
contains a different part of the original germ-plasm which had been
disintegrated in the process of the division of the ovum and the first
few blastomeres; and it does not matter that these hypotheses are
compelled to assume that a part of the original germ-plasm remains
intact, being destined to form the gonads of the adult animal. These
are hypotheses invented to account for the differentiation of the
embryo in terms of eighteenth-century physics and chemistry, and they
have yet to be supported by experiment before we can accept them as a
_description_ of what is to be observed in the processes of nuclear
division and segmentation. Further, it is certainly the case that any
one cell of the early embryo can give rise to any part of the larva.
The segmented embryo is therefore a system of parts, all of which are
potentially similar to each other. But actually each of these parts
has a different fate in the process of the development of the larva,
and this fate depends on what is the fate of the adjacent cells. There
is also a plan or design in the development of the embryo--that is,
a very definite structure results from this process--and each of the
cells shares in the evolution of this design. The system of cells is
therefore an harmonious equipotential system. The cells themselves are
not the ultimate parts of this system, for each of them is an aggregate
of a very great number of substances which are physico-chemically
characterised--at least our methods of analysis seem to show that each
cell is a mixture of a number of chemical compounds, but we must never
forget that it is the dead cell which we thus subject to analysis, and
not a living organism. Let us call these supposed chemical constituents
of the living cells the elements of the system; then at the beginning
of the process of development the latter is composed of elements
which are not definitely arranged but which are distributed in an
“homogeneous” manner very like the distribution which is effected
on shuffling a pack of cards. But as differentiation proceeds, the
elements of this system become unequally distributed, and the diversity
becomes greater and greater, attaining its maximum when the definitive
tissues and organs of the adult become established, just as at the
close of a game of bridge the cards acquire a particular arrangement
indicative of a very definite plan which was present in the minds of
the players shortly after the game began.
Mechanistic biology would seek to explain this transformation of a
homogeneous system of elements into a heterogeneous and specific
arrangement by the interaction of the elements with each other, and by
the reaction of the environment. But, given a homogeneous arrangement
of elements capable of interacting with each other, then only one final
phase can be supposed to be produced. A mixture of sulphur, carbon
dust, copper and iron filings raised suddenly to a high temperature
will only interact in one way, and the final phase of the system will
depend on the composition of the mixture, on the temperature, and
on the conduction of heat into the mixture in the initial stage of
heating. A mixture of chloroform and water shaken up in a bottle is at
first a “homogeneous” mixture of the particles of the two substances,
but under the influence of gravity the liquids separate from each other
and form two distinct layers, each of which will contain in solution
some of the other liquid. A homogeneous mixture of different substances
therefore becomes a heterogeneous arrangement in the inorganic system,
as in the organic one, but while we can predict the former one we
cannot predict the latter. We can express the result of the combination
of the elements of the inorganic mixture as something that depends
on chemical and physical potentials, but this is quite impossible
in the case of the development of the embryonic system. It is not
only that our knowledge of the developmental process is imperfect:
the distinction between the two processes of differentiation is a
fundamental one. A change in the conditions under which the inorganic
system differentiates leads of necessity to a different final phase,
but a change in the conditions under which the embryo develops need
have no such effect. If some unforeseen occurrence takes place--some
artificial interference with the process of segmentation, which could
never have been experienced in the racial history of the organism--a
_regulation_ by the parts of the embryo occurs, and the final phase of
development may be the same as if no interference had been experienced.
That which is operating in the development of the embryo is something
that is permitting, or suspending, or arranging physico-chemical
reactions.
Let us think of the developing embryo merely as an aggregation of
substances contained in an inorganic medium: the segmented frog’s egg
floating on the water at the surface of a pond is an example. As an
inorganic system its fate is determined. Autolysis of the substances
in the cells will occur and the proteids will break down with the
formation of amido-bodies, while other chemical changes, strictly
predictable if our knowledge of organic chemistry were more complete
than it is, would also occur. Putrefactive and fermentative bacteria
will attack the proteids, fats, and carbohydrates, and in the end our
aggregation of chemical substances will become an aggregation of much
simpler compounds--water, carbon dioxide, marsh gas, sulphuretted
hydrogen, phosphoretted hydrogen, ammonia, nitrates, etc., all of
which will dissolve in the water of the pond, or will diffuse into
the adjacent atmosphere. But in the living embryo this is not what
occurs: an entirely different, and much more complex, arrangement of
the chemical substances originally present in the segmented egg, or
at least a physical and chemical re-arrangement, is brought about.
The entelechy of the developing embryo prevents some reactions from
occurring and directs the energy which is potential in the system
towards the performance of other reactions.
Two analogies, suggested by Driesch, will perhaps make the rôle of
entelechy more clear. A workman, a heap of bricks, some mortar, some
food, and some oxygen constitute a system in the physico-chemical
sense. From his heap of bricks and mortar the workman may build one of
several different kinds of small house, or he may perhaps construct
several walls without any definite arrangement, or he may merely
convert one “disorderly” heap of bricks and mortar into another
“disorderly” heap. In the same way a man, a case of movable types, some
food, and some oxygen constitute another system. The initial phase of
this system consists of the compositor, his food, and some fifty-odd
boxes of types, each of which contains a large number of similar
elements. A final phase of the system may be the arrangement of the
types to form an epic poem, or a series of dramatic criticisms, or a
meaningless jumble of correctly spelt words. In all these cases the
same amount of energy was expended: the bricklayer used up the same
quantity of food and oxygen and excreted the same quantities of water,
carbon dioxide, and urea, whether he made a house, or a small chimney,
or a heap of bricks without architectural arrangement. The system of
bricks and mortar acquired during the process of differentiation a
gradually increasing complexity; while in the case of the type-setting
the diversity of arrangement acquired in the final phases may be of a
very high order. Yet the intelligent mind of the worker remained in
either case unchanged.
Let us consider further a man walking along the ties, or sleepers, of
a railway track. The ties are at variable distances apart, so that
the steps of the walker must vary in length, being sometimes closer
together, sometimes further apart. The _mean_ step has a definite
length and requires the expenditure of a certain amount of energy, and
the condition that the man takes sometimes a long step and sometimes
a short one does not require that the energy expended on the steps
should be more than if every one of them were of the mean length, for
the additional energy that is required for the long steps is saved from
the short ones. That which operates here is the power of regulation
exercised by the walker regarded as a mechanism. There is no purely
inorganic process precisely similar to this. It might be thought that
the governor of a steam engine did very much the same thing, admitting
more steam into the cylinder when the load on the engine increases,
and _vice versa_. But the governor is a mechanism _designed_ to
compensate for variations _that are given in advance_. In the case of
the man walking on the railway track, entelechy operates by suspending
energetic happening (the muscular contractions of the short steps) when
necessary, and allowing it to proceed when necessary. Entelechy itself,
whatever it may be, need not be affected by these regulations.
The organism is therefore an aggregation of chemical substances
arranged in a typical manner. These substances possess energy in the
potential form, capable of undergoing transformation so that they may
give rise to other chemical substances--secretions, for instance--or
to energy in the kinetic form, that is, the movements of muscles. In
the resting organism these transformations do not take place: the
energy remains potential, so that chemical happening is suspended. In
the unfertilised ovum, for instance, nothing happens although all the
potentialities of segmentation are contained in the cell. If reactions
did occur in consequence of the chemical potentials contained in the
substances of the cells, the progress of these would be such as to lead
to the formation of substances in which potential energy was minimal,
and in which the original energy of the cell would be represented by
the un-co-ordinated kinetic energy of the molecules resulting from the
breakdown of the substances undergoing the chemical changes. This is
not what happens in the differentiation of the ovum: the developing
cell forms new substances from those of its inorganic medium similar
to the substances of which it is already composed, and then these
substances become arranged to produce the specific form of the organism
into which the ovum is about to develop.
All hypotheses which attempt to describe the functioning of the
differentiating ovum, or the functioning organism, in terms of the
physical concepts of matter and energy alone, fail on being subjected
to close analysis. The manifestations of the life of the organism are,
it is said, particular “energy-forms,” of the same order as light,
heat, chemical and electrical energy, etc. All these energy-forms
are “concatenated,” that is, each can be converted into any of the
others. A particular frequency of the vibration of the ether can be
converted into a movement of the molecules of a material body, and so
become heat, while chemical energy may become converted into electrical
energy, or _vice versa_, and so on. It is said that life may be merely
a transformation of some “energy-form” known to us: the potential
energy of food may be converted into “biotic energy,” and this may
then manifest itself in the characteristic behaviour of the organism.
This is the method of physical science. Energy continually disappears
from our knowledge: the mechanical energy which was employed to carry
a weight to the top of a hill, or that which raises a pendulum to the
highest point of its swing, apparently disappears. If we pass a current
of electricity through water, energy disappears, for it requires more
current to pass through water than through a piece of metal of the
same section. In these and similar cases physics invents potential
energies in order to preserve the validity of the law of conservation.
The kinetic energy of the weight, or that of the swinging pendulum,
becomes the potential energy of the weight resting at the top of
the hill, or that of the bob of the pendulum at its highest point,
while the electrical energy that has apparently been lost becomes the
potential energy of the changed positions of the molecules of oxygen
and hydrogen. This assumption that the visible kinetic energy of motion
becomes converted into the invisible potential energy of position
is justified by our experience, for (neglecting dissipation) we can
recover this lost energy, in its original quantity, from the condition
of the bodies which became changed physically when the kinetic energy
disappeared. Apply the same method to the phenomena of the organism and
suppose that the chemical potential energy of the food consumed becomes
converted into the kinetic energy of motion of the parts of the body:
we are justified in this assumption by the results of physiology. But
then some of this chemical energy undergoes a transformation of quite
another kind and becomes the “biotic energy,” which is apparently that
which is in us which enables us to perform regulations, or establishes
that condition which we call consciousness. We cannot say exactly what
this “biotic energy” is, or what are the steps by which the energy
of food becomes converted into it; but no more can we say what is
electrical energy, nor what are the steps by which chemical energy
becomes converted into it. Thus our ignorance of the precise nature
of the energy-transformations of inorganic things--an ignorance which
is all the while disappearing--becomes the excuse for a comparison of
these with vital transformations, and for the assumption that there is
a fundamental similarity in the two kinds of happening.
Less is assumed in the assumption of an entelechian agency than in
assuming that the manifestations of life are the consequences of a
vital “energy-form,” different from inorganic forms, though belonging
to the same order, inasmuch as it may be concatenated with these
inorganic energy-forms. We need not suppose that a particular kind of
transformation occurs only in the sphere of the organic: all that we
need assume is that, by some agency inherent in the activities of the
organism, chemical reactions that would occur if the constellation
of parts were an inorganic one are suspended. Nothing unfamiliar to
physical science is involved in this assumption. Hydrogen and chlorine,
gases that combine together when mixed with the production of heat and
light, may be mixed under conditions such that the combination may be
delayed for an indefinite time. Iron which dissolves in nitric acid
may nevertheless be brought into the “passive” form when it remains in
contact with the re-agent but is not dissolved by it. Enzymes which
are in contact with the walls of the alimentary canal do not dissolve
these membranes so long as the tissues are alive, and they do not
dissolve the food stuff until they have been “activated.” Oxygen which
is contained in the tissues does not oxidise the tissue substances
until an enzyme or a catalase has exerted its influence. More and more,
as physiology has become more searching in its study of the functions
of the animal, has it sought to explain the metabolic processes
by assuming the intervention of enzymes, until the number of these
substances has become legion, and much of the original simplicity of
the notion of ferment-activity has been lost. But why do not these
enzymes, if they are always present in the tissues, always act? They
must be activated, says modern physiology; that is, the enzyme really
exists in the tissues as a “zymogen” or a substance which is not, but
which may become, an enzyme; or they exist as “zymoids,” that is,
substances which appear to be chemically enzymes, but which must be
activated by “kinases” before they can become functional.
Undoubtedly it is along these lines that physiology is making advances,
has increased our knowledge of the _activities_ of the animal, and is
conferring on the physician greater power of combating disease; but
the hypotheses of the activity of the enzymes is obviously one which
has been based on the results of the physico-chemical investigation
of inorganic reactions, and it has taken the precise form it has
because of the attempted analogy of many metabolic processes with
catalytic processes. Why do the inert zymoids become activated by the
kinases just when they are required by the general economy of the
whole organism? We do know that kinases are produced by the entrance
of digested food into certain parts of the alimentary canal, and that
these kinases are carried in the blood stream to other parts where
they activate the zymoids already there. But of the nature of the
machinery by means of which all this is effected physiology gives us no
hint, and it is an assumption that the mechanism involved is a purely
physico-chemical one. Suppose we say that the entelechy of the organism
possesses the power of suspending the activation of the enzyme, that
is to say, of arresting the drop of chemical potential involved in the
process of the hydrolysis of (say) a proteid. When this process of
hydrolysis is necessary in the interest of the organism entelechy can
then institute the reaction which it has itself suspended: all this
is in accord with the law of conservation. Entelechy does not cause
chemical reactions to occur which are “impossible”: it could not, for
instance, cause sulphuric acid and an alkaline phosphate to react with
the formation of hydrochloric acid. But chemical reactions which are
possible may be suspended, and suspended reactions may then become
actual when this is necessary in the interest of the organism.
Entelechy is therefore not energy, nor any particular form of
energy-transformation, and in its operations energy is neither used
nor dissipated. In all that it does the law of conservation holds with
all the rigidity with which we imagine it to hold in purely inorganic
happening--at least we need not assume that it does not hold--and this
is the essential difference between the entelechian manifestations and
the manifestations of the “vital” or “biotic” forces or energies of the
historic systems of vitalism. It is essentially arrangement, or order
of happening, and it is therefore a non-energetic agency. The workman
who may build half-a-dozen zigzag walls, or an archway, or a small
house, from the same materials and with the expenditure of the same
quantity of energy, is indeed an energetical agent, but he is more than
that. He is a physico-chemical system in which any one phase is not
determined by the preceding phase. Different results may arise from the
same initial arrangement of materials and energies, and this is because
the system contains more than the material and energetical elements.
It contains the intelligence or entelechy of the workman.
What is this entelechy? Sooner of later in all our speculation on
organic happening we must cross the arbitrary line which divides the
space of our concepts from the non-spatial--the intensive from the
extensive. Just as the physicists have left materiality behind them
in their speculations and treatment of the phenomena of radiation, so
biology must attempt to trace back the materiality of the organism to
something which is immaterial. Just as physics has now abandoned the
idea of matter as something which consists of discrete particles, or
atoms, having extension in space, and which therefore exclude each
other, so biology must seek the origin of living things, not in the
hypothetical “biophoridæ,” or other ultimate living material particles,
but in the intensive manifoldness of entelechy. There is a manifoldness
in the potentiality which the simple and homogeneous ovum possesses
of becoming the heterogeneous adult organism. This manifoldness, says
the mechanistic biologist, consists of a manifoldness of extended
material units, the determinants of Weismann, and the organisation
that arranges these units--what is this organisation? It cannot be
a three-dimensional machinery, as all close analysis of the facts
of development and regulation shows. It is then something that is
intensive, something which is not in space, but which _acts into
space_, and the result of which is manifested in spatial material
arrangements and activities. Vague and incomprehensible as is this
concept of the activities of the organisms, it is only vague and
incomprehensible because we have been accustomed to express all
chemical and physical happening in terms of the fundamental concepts
of matter and energy, and the science of the last two centuries
has left us with a terminology which applies strictly to operations
in which only these concepts are involved. But if, as all minute
analysis of vital phenomena shows, the search for the antecedents of
some energetic, material, extended system of elements in a preceding
energetical, material, extended system of elements only leads to
confusion and contradictions, then this concept of an agency which
is neither energetic, nor material, nor spatial must be formulated.
Entelechy, then, is not energy, but rather the arrangement and
co-ordination of energetic processes. It is not something that is
extended in space, but something which acts into space. It is not
material, but it manifests itself in material changes. It is a
manifoldness, or organisation, but the manifoldness is an intensive
one. Compare this definition with the notion of the ether of space
now accepted by the mathematical physicists, and it will be seen that
our speculations are similar to those of the physicists, and, like
them, the test of their reality and usefulness is to be justified
pragmatically.
* * * * *
We may now attempt a formal description of the organism based on the
discussions of the previous chapters.[34]
[34] This description is largely an expansion of Driesch’s “Analytical
definition of the individual living organism.” The reader should note
also that it includes the Bergsonian idea of duration, and that of the
organism as a typical phase in an evolutionary flux, as parts of the
description.
_The organism is a typical constellation of physico-chemical parts or
elements._
That is to say, it is an object in nature possessing a definite form,
which is the result of the arrangement of its tissues. Each tissue is
again an arrangement of cells, and each cell is a complex of chemical
substances. The organism therefore resembles, so far as our definition
goes, an inorganic crystal. But it is the typical organism that
we are considering, and this is a pure conception, for our typical
organism does not occur in nature. The organisms that are accessible
to our observation are constellations of physico-chemical parts, but
these constellations tend continually to deviate from the conceptual
arrangement. Progressive variation from the type is something that
distinguishes the organic constellation from the inorganic one.
_The organism is an entity in which energy-transformations of a
particular nature are effected. These transformations raise energy from
a state of low, to a state of high potential._
This is the general tendency of terrestrial life, and it is
expressed most fully in the metabolism of the green plant. The
energy-transformations that are effected here are those in which the
kinetic energy of radiation is employed to build up chemical compounds
of high potential, from inorganic substances incapable in themselves
of undergoing further transformations. The general tendency of all
inorganic transformations is towards inertia. In them energy is not
destroyed, but it is dissipated: it becomes uniformly distributed
throughout material bodies as the un-co-ordinated motions of the
molecules of which those bodies are composed, and it ceases to be
available for further transformations. The green plant reverses
this transformation, and accumulates energy in the form of chemical
compounds of high potential. Inorganic processes are those in which
available energy becomes unavailable, and this unavailable energy can
only become available again if a compensatory energy-transformation
is effected. Life is that which effects these compensatory
energy-transformations.
_The organism is a constellation capable of indefinite growth by
dissociation._
That is to say, it is a constellation which reproduces itself in all
its specificity. Growth consists in the separation from the organism
of a part, or reproductive cell, which divides (or dissociates)
repeatedly, each dissociated part growing again in mass by the addition
of substances similar to its own, but which are taken from a medium
dissimilar in composition to itself. The aggregate of parts so formed
then differentiates so that the constellation is reproduced in all its
specificity. There is nothing precisely similar to this in inorganic
happening. The growth of a crystal consists simply of the accretion of
elements similar in nature to those of the growing body, and there is
no differentiation.
_The organism exhibits autonomy._
It is a constellation which persists in the midst of an ever-changing
environment, and the typical organic form remains the same, although
the material of which it is composed undergoes continual change. There
are inorganic entities which resemble the organism in this respect: the
form of a cyclone or atmospheric disturbance, for instance, remains
the same even though the air of which it is composed is continually
changed. But the form of the organism does not vary strictly with the
changes in the environment in which it is placed, for it may respond to
an environmental change by a regulation, or compensatory change in form
or functioning, the effect of which is to maintain the constellation
in all its specificity. The regulation is not a complete or perfect
one, for environmental changes do, to some extent, produce changes in
the organic constellation, but there is no functionality between the
environmental change and the organic response. In inorganic happening a
change in one part of a transforming system necessarily determines the
nature and extent of the changes that occur in the other parts of the
system.
_The organism is a centre of continuous action._
It is first of all a part of nature in which energy-transformations
continually take place--a description which applies equally well to
plants and animals. It is only when we attempt to seek an inorganic
system to which this definition would apply that we find how well it
differentiates the organic from the inorganic. An inorganic system
which transforms energy is either one which tends continually towards
stability, or it is a machine made by man for a definite purpose, and
it is therefore a system involving a teleological idea. An organic
centre of action is one in which energy-transformations proceed without
cessation.
In the plant organism the energy-transformations represent, with the
exception of the reproductive processes, the whole activity of the
organism. In the animal organism they are accessory to regulated and
purposeful motile activity, that is, muscular action. The object of
this muscular activity varies with the stage of evolution attained by
the animal. Its sole object in the lower animal is that of individual
or racial preservation. Living in an organic and inorganic environment
which is always hostile and tends continually towards its destruction,
the whole activity of the organism is directed to the attempt to master
this environment: it struggles for its individual existence, and that
of its offspring. The activities of man are also these, but they are
more than these, for, knowing that physical processes tend continually
towards inertia, he seeks to control these processes, and to preserve
the instability of nature on which the possibility of further becoming
depends.
The activity of the organism, whether it be the energy-transformations
of the plant or the motile activities of the animal, are directed and
regulated activities. The activity of the organism is not a functional
activity in the sense that the activity of a dynamo is a function of
the nature of the machine, and of the nature and quantity of the energy
supplied to it. The nature of the activity of the organism is regulated
autonomously by purposes which it “wills” to carry out.
_The organism is a phase in an evolutionary flux._
Categories of organisms--varieties, species, genera, etc.--are
fictions. They are arbitrary definitions designed to facilitate our
description of nature. They are types or ideas. In constructing them
we follow the method of the intellect, and we represent by immobility
that which is essentially mobile and flows. Between the fertilised egg
and the senile organism there is absolute continuity. Our description
of the individual organism is a description of it at a typical moment
of its life-history, and this description includes all that has led up
to, as well as all that will fall away from, the morphology at this
particular typical moment.
Even then the arbitrarily defined organism is only a phase. In
defining it we arrest, not only the individual, but also the racial,
evolutionary flux. The specific morphology is that of a typical
moment in a racial flux. Leading up to it at this moment are all the
variations that have joined it with its ancestry, and leading away from
it will be all the variations that will convert it into its descendants.
The individual and racial developments are true _evolutions_. They are
the unfolding of an organisation which was not expressed in a system
of material particles or elements interacting with each other, and
with the elements of the environment, but which we must seek in an
intensive, non-spatial manifoldness.
In the evolutionary flux the changes are non-functional ones, that
is to say, any phase, whether it be one in an individual or a racial
development, is not merely a rearrangement of the elements of the
preceding phases, as in the case of a transforming system of material
particles and energies. There is inherent, spontaneous variability.
_The organism endures._
That is, all its activities persist and become part of its
organisation. It does not matter whether or not we decide that
characters which are acquired are transmitted, nor does it matter
whether or not we conclude that the environment is the cause of these
acquirements. Some time or other in the individual or racial history
new characters arise by the activity of the organism itself, and
these characters either persist in an individual or in a race. They
endure. All its activities, even its thoughts, persist and form the
experience of the animal--an experience which continually modifies its
conduct. In man those true acquirements, the results of education and
of investigation, persist as written language, or as tradition, even if
they are not inherited.
Duration is not time. The mathematician does not employ, in his
investigations, intervals of duration. When he relates something which
is happening now to something which happened some time ago he employs
the differential co-efficient _dy/dx_, so that the interval between the
two occurrences becomes an “infinitesimal” one. When the astronomer
predicts events that will happen some years hence, or describes those
that happened some years ago, he is really describing things that are
all there at once, so to speak, things which are given. If we unfold
a fan, stick by stick, we see the separate members in succession, but
they are all there, and we can, if we like, see them all at once.
The more we reflect on it the more we see that mathematical time is
only a way in which we see things apart from each other. Things become
extended in time as they become extended in space. Whether occurrences
capable of analysis by the methods of physics are what we call past or
future occurrences, they are all given, in that each of them is only a
phase of the others.
Duration belongs to the organism. The past is known because all that
has occurred to the organism still persists in its organisation.
The future is unknown because it has still to be made. Duration is
therefore a vector--something having direction, and the organism
progresses out of the past into the future. It grows older but not
younger.
* * * * *
Such appears to be the nature of life. Can we discuss the problem of
its _origin_?
Did life originate on our earth? We must first consider what we mean
when we speak of an origin. The organic world of the present moment,
with all its environment--that is to say, the totality of organisms
on the earth, with all the materials which they can utilise in any
way, the energy of radiation from which they ultimately derive
their energy, and all the parts of the cosmos which interact with
them--constitute a system in the physical sense. The present condition
of the organic world, that is, the kinds and numbers of organisms,
and their distribution, and the distribution of the materials which
they can utilise, and the quantity and nature of the energy which
is available to them, are the present phase of this system. All
the conditions of life in the past, that is to say, the kinds, and
numbers, and distribution of organisms, and the quantity and nature
of their environment at any time, together formed phases of this
system. If there was a time when life, as we know it, did not exist,
then the materials and the energies, which were antecedent to life
when it did appear, were also a phase of the system. On a strictly
mechanistic hypothesis there could be no origin: there could only be
a transformation of a system which was already in existence. All that
exists to-day was given then. When, therefore, we speak of the origin
of life from non-living materials we mean simply a transformation of
those materials and energies.
There was a time, it is said, when life could not exist on the earth.
For the organism is essentially that aggregate of chemical compounds
which we call protoplasm, and this cannot exist at temperatures higher
than 100° C., and it cannot function at temperatures lower than 0° C.
It requires carbon dioxide, and ammonia or nitrate, as the materials
for its constructive metabolism, and there was a time when these
compounds could not exist, for they must have been dissociated by
the heat of the gaseous nebula from which our earth originated. The
organism requires energy in the form of solar radiation of a particular
frequency of vibration, and there was a time when the sun’s radiation
was different from what it is now. Therefore life did not exist then.
Even if we believe that life came to the earth as germs, which existed
previously in outer cosmic space, this belief does not solve the
problem, which simply becomes transferred from our earth to some other
cosmic body.
But life, as we know it, makes use of the materials and the energies
which are available to it in the conditions in which it exists. The
plant organism obtains its energy from solar radiation because this
is the most abundant source of terrestrial energy. The human eye is
most susceptible to light of a particular frequency of wave-length,
but this is the radiation that is most abundant in the light of the
sun. Does this not mean that the organism has merely adapted itself
to the material and energetic conditions in which it exists? Does it
necessarily mean that because the conditions were very different life
could not exist? Protoplasm could not exist at a temperature of several
thousand degrees Centigrade, but does that mean that life, which on any
hypothesis of mechanism must be described in terms of energy, could not
exist in these conditions?
It must have had an origin, says Weismann, because it has an end.
Organic things are destroyed, inasmuch as they disintegrate into
inorganic things. Organisms die. Thus the organic process comes to
an end, and because it comes to an end it must have a beginning.
Spontaneous generation of life is thus, for Weismann, a “logical
necessity.”
Need this logical necessity exist? The argument clearly implies that
life is a reversible process. Organic things become inorganic, and
therefore inorganic things must become organic things. The first
statement is a fact of our experience, but the second one would only
be logically true if we were to postulate that the process of life,
whatever it may be, is a reversible process. But we must not postulate
this if we are to hold to a physico-chemical mechanism, for it is
a fundamental result of physical investigation that all inorganic
processes are irreversible: reversible inorganic processes are only
the limits to irreversible ones. Physical processes go only in one
way, and that organic substance is destroyed to the extent that it
becomes inorganic is a particular case of this irreversible physical
tendency. Now the mechanism of Weismann must base itself on the
concepts of physics and chemistry, and it must postulate the origin
of life from non-living substances. Why? Because life is a reversible
process, that is, it exhibits a tendency which does not exist in
inorganic processes. Clearly the logic is faulty! And must we conclude
that life has an end? Weismann himself suggests that nothing in the
results of biology indicates that physical death is a necessity: it
is rather an adaptation. The soma, or body, is the envelope of the
germ-plasm, and exposed as it is to the vicissitudes of an environment
which is always hostile, it becomes at length an unfit envelope. But
with the reproductive act the germ-plasm acquires a new soma, and it
is no longer necessary that the former one should continue to exist as
an unfit envelope. Physical death therefore occurs as an adaptation
serving for the best interests of the race. The organism need not die,
for the germ-plasm may be a physical continuum throughout innumerable
generations. Somatic death is only a destructive metabolism: it is a
catastrophic metabolism, if we like.
We may legitimately discuss such problems as the origin of
the protoplasm of the prototrophic organism, or that of the
chlorophyll-containing cell, or that of the nerve-cell. On the
mechanistic view each of these conditions is a phase of a transforming
physico-chemical system, and it is within the scope of the methods of
physical science to investigate the nature of these transformations.
But if the argument of this book is sound, then the problem of the
origin of life, as it is usually stated, is only a pseudo-problem;
we may as usefully discuss the origin of the second law of
thermo-dynamics! If life is not only energy but also the direction
and co-ordination of energies; if it is a tendency of the same
order, but of a different direction, from the tendency of inorganic
processes, all that biology can usefully do is to inquire into the
manner in which this tendency is manifested in material things and
energy-transformations. But the tendency itself is something elemental.
APPENDIX
MATHEMATICAL AND PHYSICAL NOTIONS[35]
[35] It must be understood that some of the things dealt with in these
appendices are very hard to understand by the reader acquainted only
with the results of biological science. We urge, however, that they are
all relevant if biological results are to be employed speculatively.
INFINITY
What is really meant when the mathematician uses the concept of
infinity in his operations? Suppose that we take a line of finite
length and divide it into halves, and then divide each half into
halves, and so on _ad infinitum_. We make cuts in the line, and these
cuts have no magnitude, so that the sum of the lengths into which we
divide the line is equal to the length of the undivided line. We can
divide the line into as many parts as we choose, that is, into an
“infinite” number of parts.
Suppose that we are making a thing which is to match another thing, and
suppose that we can make the thing as great as we choose. If, then, no
matter how great we make the thing, it is still too small, the thing
that we are trying to match is infinitely great.
Substitute “small” for “great,” and this is also a definition of the
infinitely small.
Clearly the idea of infinity does not reside in the _results_ of
an operation, but in its tendency. It inheres in our intuition of
_striving_ towards something, but not in the results of our striving.
FUNCTIONALITY
If we pour some mercury into a U-tube closed at one end, the air in
this end will be contained in a closed vessel under pressure. We can
increase the pressure by pouring more mercury into the open end of the
tube. We can measure the volume of the air by measuring the length of
the tube which it occupies. We can measure the pressure on this air by
measuring the difference of length of the mercury in the two limbs of
the tube. By taking all necessary precautions we shall find that for
each value which the pressure attains there is a corresponding value of
the volume of the air.
We thus find the pressure values, _p_↓{1}, _p_↓{2}, _p_↓{3}, _p_↓{4},
_p_↓{5}, etc., and the corresponding volumes, _v_↓{1}, _v_↓{2},
_v_↓{3}, _v_↓{4}, _v_↓{5}, etc., and we may then plot these values so
as to make a graph.
[Illustration: FIG. 27.]
In this figure the values represented along the horizontal axis are
pressure-values, and those represented along the vertical axis are
volume-values. We have so made the experiment that we can make the
pressure-values whatever we choose--let us call them the values of the
_independent variable_ or _argument_. For each value of the pressure,
or argument, there is a corresponding value of the volume, which
_depends_ on the pressure--let us call these values of the volume
values of the _dependent variable_ or _function_.
We can make arbitrary values of the pressure, but whenever we do
this the corresponding values of the volume are fixed. We say, then,
that the volume is a _function of the pressure_. In general, when we
choose one value of an independent variable, or argument, there can
be only one, or a small number, of values of the dependent variable,
or function. If there are two or more values of the function for one
value of the argument each of these is necessarily determined by the
value which we choose to assign to the argument. There is a strict
_functionality_ between the two series of variables. In the experiment
we have chosen this functionality is expressed by the equation _pv_ =
_k_(_1_ + _at_), where _p_ is the pressure, _v_ the volume, _k_ and
_a_ constants, and _t_ is the temperature at which the experiment
is carried out. In a number of experiments like that which we have
mentioned, _k_, _a_, and _t_ are the same throughout, and this is why
we call them _constants_. We give _p_ any value we like, and then _v_
can be calculated from the equation.
RATE OF VARIATION
If we know the equation _pv_ = _k_(_1_ + _at_), we can find how much
the volume changes when the pressure changes, that is, the rate of
variation of _v_ with respect to _p_. But even if we don’t know that
this equation applies, we can still find the rate of variation from our
experiments. We see from the graph that, when the pressure increases
from _p_↓{1} to _p_↓{2}, the volume decreases from _v_↓{1} to _v_↓{2}
but that if the pressure is again increased to _p_↓{3}, that is, by a
similar amount to the increase of pressure from _p_↓{1} to _p_↓{2}, the
volume decreases from _v_↓{2} to _v_↓{3}. Now we find, by measurements
made on the graph, that the decrease _v_↓{1} to _v_↓{2} is greater than
the decrease _v_↓{2} to _v_↓{3}, and the latter decrease is greater
again than the decrease from _v_↓{3} to _v_↓{4}. Evidently the rate
of variation of volume is not like the rate of variation of pressure,
that is, the same throughout, and when we look at the graph we see
that the rate of variation is greatest where the slope of the curve is
steepest. The latter is steepest near the point _a_, less steep near
the point _b_, and still less steep near the point _c_. Now any _small_
part of the curve is indistinguishable from a straight line. Let us
draw a straight line _ee_↓{1}, which appears to coincide with a small
part of the curve near _a_, and similar straight lines _ff_↓{1}, and
_gg_↓{1}, which also appear to coincide with small parts of the curve
near _b_ and _c_. Then the steepness of the curve will be proportional
to the angles which these straight lines make with the axis _op_, and
these angles are measured by their tangents, that is, by the ratio
_oe_↓{1}/_oe_, which is the tangent that _e_↓{1}_e_ makes with _op_,
the ratio _of_↓{1}/_of_, and the ratio _og_↓{1}/_og_.
[Illustration: FIG. 28.]
The point _a_ on the curve corresponds with a pressure _a_↓{1} and a
volume _a_↓{11}. The point _b_ corresponds with a pressure _b_↓{1}
and a volume _b_↓{11}, and _c_ with a pressure _c_↓{1} and a volume
_c_↓{11}. The _average_ rate of variation of the volume of the gas, as
the pressure changes from _a_ to _c_, is therefore proportional to the
sum of the tangents _oe_↓{1}/_oe_ and _og_↓{1}/_og_, divided by 2.
THE NOTION OF THE LIMIT
Suppose that we wish to find the rate of variation of volume for a
pressure change in the immediate vicinity of the value _b_↓{1}, that
is, the rate of variation as the pressure changes from a little less
than _b_↓{1} to a little more than _b_↓{1}. If we find the point _b_
on the curve corresponding to _b_↓{1}, and if we then draw a line
_ff_↓{1}, _touching_ the curve at the point _b_, we shall obtain the
angle _off_↓{1}. It might appear now that the tangent of this angle,
that is, the ratio _of_↓{1}/_of_, would give us a measure of the rate
of variation of volume.
But the reasoning would be faulty. The line _ff_↓{1} only _touches_
the curve, it does not coincide with an element of the curve. Also at
the point _b_↓{1} the pressure has a certain definite value, and there
is no change. At the corresponding point _b_↓{11} the volume also has
a certain definite value, and there is no change. There can therefore
be no rate of variation. The value of the tangent does not give us a
measure of the rate of variation: it gives us the _limit_ to the rate
of variation, when the pressure is changing in the immediate vicinity
of _b_↓{1}.
We must stick to the notion of a pressure change in the _immediate
vicinity_ of _b_↓{1}. What do we mean by “immediate vicinity”? We
mean that we are thinking of a range of pressure-values in which
the particular pressure-value _b_↓{1} is contained, but not as
an end-point. We mean also that we choose a definite standard of
approximation to the value _b_↓{1}, so that any pressure-value within
our interval differs from _b_↓{1} by _less_ than this standard of
approximation. It means further that, no matter how small is the number
representing this standard of approximation, _any_ pressure-value
within the interval will differ from _b_↓{1} by less than this number.
This is what we really mean when we say that the interval we are
thinking about is an “infinitely small one.”
Now corresponding to this interval of pressure-values in the immediate
vicinity of _b_↓{1}, there will be an interval of volume-values in
the immediate vicinity of _b_↓{11}, and, as before, any one of these
volume-values will differ from _b_↓{11} by less than any number
representing a standard of approximation to _b_↓{11}. We then find
the point on the curve corresponding to both _b_↓{1} and _b_↓{11},
that is b, and we draw the line _ff_↓{1}, and find the tangent of the
angle which this line makes with _op_. The value of this tangent is
the _limit_ of the rate of variation of the volume of the gas when the
pressure undergoes a change in the immediate vicinity of _b_↓{1}.
“Rate of variation” is a function of the argument “pressure.” This
function has the limit _l_ for a value of its argument _b_↓{1}, when,
as the argument varies in the immediate vicinity of _b_↓{1}, the value
of the function approximates to _l_ within _any standard whatever_ of
approximation.[36]
[36] If the reader does not understand this, he should read Whitehead’s
“Introduction to Mathematics.” He should read this book in any case.
We should not, of course, find the rate of variation of volume of the
gas by this means. We should calculate the value of the differential
co-efficient _dv_/_dp_ from the equation _pv_ = _k_(_1 + at_): this
would be _k_ (_1 + at_)/_p_^2. But the reasoning involved in the
methods of the calculus are those which we have attempted to outline.
We try to avoid the terms “infinitely small,” “infinitely near,”
“infinitely small quantities,” and so on, by the device of standards
of approximation. It may appear to the non-mathematical reader that
all this is rather to be regarded as “quibbling,” but the success of
the methods of mathematical physics should convince him that such is
not the case. He should also reflect that clear and definite ideas
on the fundamental concepts of the science are just as necessary in
speculative biology as they are in mathematics.
(Another example.)
Let us consider the case of a stone failing from a state of rest.
Observations will show that when the stone has fallen for one second
it has traversed a space of 16 feet; at the end of two seconds it has
fallen through 64 feet; and at the end of three seconds the space
traversed is 144 feet. From these and similar data we can deduce the
velocity of motion of the stone as it passes any point in its path.
The velocity is the space traversed in a certain time _s_/_t_. If we
take any easily observable space (say five feet) on either side of the
point chosen, and then determine the times when the stone was at the
extremities of this interval, and divide the interval of space by the
interval of time, we shall obtain the _average_ velocity of motion of
the stone over this fraction of the whole path chosen. But the velocity
did not vary in a constant manner during this interval (as we see by
considering the spaces traversed during the first three seconds of the
fall). Therefore our average velocity does not accurately represent the
velocity of the stone as it passes the point at the middle of the path
chosen.
We therefore reduce the length of the path more and more so as to make
the average velocity approximate closer and closer to the velocity
near the middle portion of the path. In this way we find the ratio
δ_s_/δ_t_, where δ_s_ is a very small interval of path containing
the point chosen, but not as an end-point, and δ_t_ is a very small
interval of time. Perhaps this average velocity may be near enough
for our purposes, but perhaps it may not. The interval of path δ_s_
is still a finite interval, and δ_t_ is still a finite time, and so
long as these values are finite ones the velocity deduced from them
remains a mean one. All that we can say is that it approximates to the
velocity, as the arbitrary point was passed, within a certain standard
of approximation.
Obviously the smaller the interval δ_s_, the closer will be this
approximation. Suppose, then, that we diminish δ_s_ till it “becomes
zero.” It might appear now that when δ_s_ coincides with the point
chosen we shall obtain the velocity of the stone at this point. But
if there is no interval of path, and no interval of time, there can
be no velocity, which is an interval of path divided by an interval
of time; and if the stone is “at the point,” it does not move at all.
We must stick to the idea of intervals of space and time, and yet we
must think of these intervals as being so small that no error whatever
is involved in regarding the mean velocity deduced from them as the
“true velocity.” We therefore think of the point as being placed in
an interval of path, but not at an end-point of this interval. We
think of the velocity as a mean one, but we must have a standard of
approximation, so that we may be able to say that the mean velocity
approximates to the “actual” or _limiting_ velocity of the stone as it
passes the point, within this standard of approximation. The smaller we
make the interval, the closer will the mean velocity approximate to the
limiting velocity.
We therefore think of the stone as moving in the immediate vicinity of
the point in the sense already discussed. We say that the “immediate
vicinity” is an interval such that any point in it, _p_↓{1},
approximates to the arbitrary point _p_ which we are considering within
any standard of approximation: that is, no point in the interval is
further away from _p_ than a certain number expressing the standard
of approximation, and this can be _any_ number, however small. We say
the same thing about the interval of time. That is to say, we make the
intervals as small as we like: they can be smaller than any interval
which will cause an error in our deduced velocity, no matter how small
this error may be.
The limit of the velocity of a stone falling past a point in its
path is, therefore, that velocity towards which the mean velocities
approximate within any standard of approximation, when we regard the
interval of space as being the immediate vicinity of the point, and the
interval of time as being the time in the immediate vicinity of the
moment when the stone passes the point. The limit of the velocity is
not δ_s_/δ_t_ but _ds_/_dt_, _dt_ and _ds_ being, not finite intervals
of time and space, but “differentials.” We determine this limit by the
methods of the differential calculus.
FREQUENCY DISTRIBUTIONS AND PROBABILITY
Let the reader keep a note of the number of trumps held by himself and
partner in a large number of games of whist (the cards being cut for
trump). In 200 hands he may get such results as the following:
_No. of trumps in his own and partner’s hands_--0, 1, 2, 3,
4, 5, 6, 7, 8, 9, 10, 11, 12, 13.
_No. of times this hand was held_--0, 0, 0, 1, 9, 29, 53,
52, 35, 14, 6, 1, 0, 0.
He should note also the number of times that trumps were spades, clubs,
diamonds, and hearts: he will get some such results as the following:
spades, 46; clubs, 53; diamonds, 51; hearts, 50.
The numbers in the lower line of the first series form a “frequency
distribution,” for they tell us the frequency of occurrence of the
hands indicated in the numbers above them. “No. of trumps” is the
independent variable, and “no. of times these nos. of trumps were held”
is the dependent variable.
A frequency distribution represents the way in which the results of a
series of experiments differ from the mean result. A particular result
is expected from the operation of one, or a few, main causes. But a
number of other relatively unimportant causes lead to the deviation
of a number of results from this mean or characteristic one. Yet
since one, or a few, main causes are predominant, the majority of
the results of the experiment will approximate closely to the mean;
and a relatively small proportion will deviate to variable distances
on either side of the mean. If a pack of cards were shuffled so that
all the suits were thoroughly mixed among each other, then we should
expect the trumps to be as equally divided as possible between the four
players. But a number of causes lead to irregularities in this desired
uniform distribution, and so the results of a large number of deals
deviate from the mean result. It is possible, by an application of the
theory of probability, to calculate ideal, or theoretical frequency
distributions, basing our reasoning on the considerations suggested
above. We then find that the observed and calculated frequency
distributions may be very much alike.
In biological investigation, far more than in physical investigation,
we deal with mean results. It is, however, just as important that the
mean should be considered as the individual divergences from the mean.
We want to know the mean results, and the way and the extent in which
the individual results diverge from the mean.
There is a mean or “ideal” result, but we must think of a great number
of small independent causes which cause the actually obtained results
to diverge from this mean. If these small un-co-ordinated causes
are just as likely to cause the results to be less than the mean,
as greater than the mean, we shall obtain a frequency distribution
resembling the one given above, in that the variations from the mean
are equal on both sides of the mean. But if the general tendency of the
small un-co-ordinated causes is to cause the results, on the whole, to
tend to be greater than the mean, then the frequency distribution will
be “one-sided,” that is, if we represent it by a curve the latter will
be an asymmetrical one. Curves which are asymmetrical are those most
frequently obtained in biological, statistical investigations.
MATTER
Our generalised notion of matter is that it is the physical substance
underlying phenomena. Immediately, or intuitively, we attain the notion
of matter because of our perceptions of touch, and our perception of
muscular exertion. The distance sense-receptors, visual, auditory, and
olfactory, would not give us this intuition of matter.
Material things are extended, that is, they have form, and they
exclude each other, so that they cannot occupy the same place. They
appear to us to be aggregates of different nature: they may be solid
and homogeneous, like a piece of metal; or solid and porous, like a
piece of pumice-stone; or loose and granular, like sand; or viscous or
liquid, like pitch or water. They may have colour. They are opaque, or
transparent in various degrees. They may have odour. Material things,
as they are perceived by the distance sense-receptors, appear to have
qualities.
Material things are aggregates of molecules. The aggregates may possess
essential form, like that of a crystal, or an organism. The form of
the aggregate may be essential and homogeneous, so that it consists
of molecules, all of which are of the same kind, like a crystal. It
may be heterogeneous and essential, like the body of the organism,
when it consists of molecules which are not all of the same kind. The
aggregates may have accidental form, like that of a river valley, or a
delta, or a mountain, and the form in these, and similar cases, is not
a part of the essential nature of the aggregate.
The molecules are selections (in the mathematical sense) of some of
about eighty different kinds of atoms. A molecule is a small number of
atoms arranged together in a definite way, and its nature depends, not
only on the kinds of atoms of which it is composed, but also on the
arrangement of these atoms. Two or more different arrangements of the
same atoms are, in general, different molecules.
MASS
When matter is perceived by the tactile and muscular sense organs, we
have the intuition of mass. It is _heavy_, and the degree of heaviness
is proportional to the quantity of matter in the body which we feel,
that is, to its mass. Heaviness is synonymous with weight, but weight
does not depend alone on the quantity of matter in the body. If the
latter were removed to an infinite distance from the earth or other
cosmic bodies, its weight would disappear, but its mass would remain.
We could still touch and move it, and we should still find that
different degrees of muscular exertion would be necessary when bodies
of different masses had to be moved.
INERTIA
If the body were in motion, we should find that muscular exertion is
necessary in order that it might be brought to rest; and if it were at
rest, we should find that muscular exertion was necessary in order that
it might be moved. The body, matter in general, possesses inertia, and
this is its most fundamental attribute. Mass we can only conceive in
terms of inertia. If two bodies were at rest, and if the same degree
of muscular exertion conferred on each the same initial velocity of
motion, their masses would be equal. If the same degree of muscular
exertion conferred different velocities on different bodies, their
masses would be different, and would vary directly with the initial
velocities conferred.
FORCE
The feeling which we experience when we move a body from a state of
rest, or stop a body which is moving, is what we call force. If on
climbing a stair in the dark we think there is one step more than there
is, and so have the queer, familiar, feeling of treading on nothing,
we have the intuition of energy; but when we tread on the steps, and
so raise our body, we have the intuition of force. Force is that which
accelerates the velocity of a mass. If the latter is at rest, we
consider it to have zero velocity. If it is moving, and we stop it,
there is still acceleration, but this is negative.
Matter, that is, the _substantia physica_, is clearly to be conceived
only in terms of energy. It is, to our direct intuitions, resistance,
or inertia, that which requires energy in order that it may be made to
undergo change. Our static idea of physical solidity, or massiveness,
disappears on ultimate analysis. Molecules are made up of atoms, and
the atoms are assumed to have all the characters of matter: we could
not _see_ them, of course, even if we possessed all the magnifying
power that we wished, for they would be too small to reflect light.
Modern physical theory is compelled to regard atoms as complex, and
imagines them as being composed of moving electrons. The electron
is immaterial--it is the unit-charge of electricity. It is said to
possess mass, but mass is now understood to mean inertia. So long as
the electron is moving, it sets up a field of energy round it, and this
field--the electro-magnetic one--extends in all directions. Periodic
disturbances in it constitute radiation, and this radiation travels
with the velocity of light. It is because of the existence of this
field that we are _obliged_ to postulate the existence of an ether
of space. Unfamiliar to us until the discovery of Hertzian waves and
“wireless” telegraphy, this electro-magnetic radiation in space is now
accessible to our direct intuitions. We can initiate it by setting
electrons in motion, that is, by expending energy (producing the
sparking in the transmitters of the wireless telegraphy apparatus); and
we can stop it, if it is in existence, by absorbing the energy (in the
receivers of the wireless telegraphy apparatus). This is essentially
what we understand by the inertia of gross matter. We set a body in
motion by expending energy on it (the explosion of the powder in a
cartridge, which converts potential chemical energy into the kinetic
energy of the moving projectile); and we can stop a body which is in
motion by absorbing this energy of motion (by causing the projectile to
strike against a target, when the kinetic energy of its motion becomes
the kinetic energy of the heat of the arrested body).
Inertia is therefore the same thing whether it be the inertia of
visible, material bodies, or the inertia of invisible, material
molecules, or the inertia of the immaterial, non-tangible ether. It is
the condition that energy-changes must occur if anything accessible to
our observation is to change its state of rest or motion.
ENERGY
Energy is therefore indefinable. It is an elemental aspect of our
experience.
Nature to us is an aggregate of particles in motion. We have to speak
of massive particles, whether we call these visible material bodies,
or molecules, or atoms, or electrons, in order that we may describe
nature. We must employ the fiction of a _substantia physica_. We only
know the substance or matter in terms of energy; it is really the
latter that is known to us. It is the poverty of our language, or
rather it is the legacy of a materialistic age, that compels us to
speak of particles that move, rather than of motions as entities in
themselves.
Considering, then, the idea of particles in motion as a fiction
necessary for clear description, we can study energy. There is only
one kind, or form, of energy which presents itself to our aided or
unaided intuitions, that is kinetic energy. Bodies that move possess
this energy represented by their motion: they can be made to do work,
that is, their energy can be transformed into other forms of energy.
All things are in motion. A gas consists of molecules incessantly
moving with high velocity, and colliding and rebounding from each
other. The energy of a gas is the sum of one-half of the masses of all
the molecules, multiplied by the squares of the velocities of all the
molecules, that is, Σ1/2_mv_^2. This is also the kinetic energy of a
projectile, or of a planet revolving round the sun. Kinetic energy is
that of the uniform, unchanging motion of some entity possessing mass,
but we must extend our notion of mass so as to include immaterial,
imponderable entities such as electrons.
This energy cannot be destroyed or created--the law of conservation
of energy. This is a principle or mode of our thought. We are unable
scientifically or philosophically to think of an entity ceasing to be.
Dreams and phantoms show us entities which are real _while they last_,
but which cease to exist. If we do attempt to think of entities that
appear from, or disappear into, nothing, we surrender the notion of
reality. The more we think of it the more clearly we shall see that the
_things which we call real are the things which are conserved_.
Yet energy, to our immediate intuitions, seems to disappear. A flying
bullet strikes against a target and becomes flattened out into a
motionless piece of lead. A red-hot piece of iron cools down to the
temperature of its surroundings. A golf-ball driven up the side of
a hill comes to rest in the grass. A current of electricity passing
through water is used up, that is, electricity of a higher potential
is required to force the current through water than to force it through
thick copper wire. In all these cases we might think that energy is
lost, but we cannot believe this. The kinetic energy of the flying
bullet becomes transformed into the increase of the kinetic energy of
the molecules of the metal of which the bullet was composed; for the
latter becomes greatly heated when its flight is arrested and this
increased heat ought to be equal to the kinetic energy of the bullet
in flight. The red-hot piece of iron cools, and the kinetic energy of
its molecules becomes less and less, but this does not cease to exist,
for the energy is simply transferred by radiation and conduction to the
surrounding bodies, the temperature of which it raises. The golf-ball
driven up the hill comes to rest and loses its kinetic energy. Some
of this has been transferred to the air through which it passes, the
latter being heated very slightly; some of it is expended by friction
with the grass over which the ball rolls before coming to rest, and
this energy is traceable in heat-effects, or in mechanical effects,
but the rest of it apparently ceases to exist. But this would be
contradictory to the principle of conservation, and so we say that the
lost kinetic energy has become potential. The current of electricity
may heat the water through which it passes, and some of the energy
which seems to disappear is so to be traced, but the greater fraction
is apparently lost. A quantity of free hydrogen and oxygen is, however,
generated, and we say that the kinetic energy of the moving electrons
has become transformed into the potential chemical energy of the
gaseous mixture.
POTENTIAL ENERGY
Therefore, if energy disappears or appears, we do not say that it is
destroyed or is created: we invent potential energies, into which
we suppose that the energies in question have become transformed, in
order that we may still think of them as being subject to an _a priori_
principle of conservation. Although a particle of radium continually
generates heat, we do not therefore think of the first principle of
energetics as being invalidated, for we suppose that the energy which
thus appears was really potential in the atoms of radium. But it
was contrary to all our former experience of atoms that they should
contain any other energy than that of their own motion, and so the
further assumption was made that the atom, at least the atom of the
radio-active substance, is really complex, and not simple, as chemical
theory demands. It is made up of smaller particles, and possesses a
definite structure. In certain circumstances the atom may disintegrate,
and the energy which held together its particles, whether these were
simpler corpuscles or electrons, is given off as the heat which the
radio-active substance apparently generates. The potential energy of
the chemical atom is therefore a hypothesis which has been devised
in order to preserve the validity of the law of conservation, and
the reality of this hypothesis is being tested by investigation. If
we accept it as true, are the deductions made from it justified in
our experience? That is the test which must be satisfied in all the
hypotheses where potential energies are invented, and the potentials
are only real if the test is satisfactory. The golf ball at rest at
the top of the hill is a different entity from the golf ball at rest
at the bottom of the hill: it is capable of developing energy, for
a touch may cause it to roll down the hill, when most of the energy
which was expended in order to drive it to the top of the hill will
reappear in the form of the kinetic energy of motion of the ball. The
atoms of hydrogen and oxygen which were dissociated by the energy of
the electric current are different things from the atoms of hydrogen
and oxygen which are combined together to form the molecules of water.
Their state when the gases are in the elementary condition, or are
“free,” is that of molecules moving rapidly and incessantly, rebounding
from each other after colliding with each other: they possess energy of
position--potential energy--because they are separate from each other.
If they “combine,” as when a minute electric spark explodes the mixture
of gases, they tractate together, and remain in proximity to each
other, becoming molecules of water. The energy which became potential
in the gaseous mixture, when the electric energy of the current seemed
to disappear, now appears as the heat generated by the combustion,
that is, as the greatly increased kinetic energy of the molecules of
the gas (steam) which takes the place of the mixture of hydrogen and
oxygen. Previous to the explosion this gas was a mixture of molecules
of hydrogen and oxygen (2H↓{2} + 2O) at the ordinary temperature, but
after the explosion it consists of a smaller number of molecules at a
very much higher temperature.
What is “energy of position”? The golf ball at the bottom of the hill
was at a distance of _R_ feet from the centre of the earth, but at
the top of the hill it is at a distance of _R_ + 100 feet from the
centre of the earth. In the first case it was free to fall _R_ feet,
but in the second case it is free to fall _R_ + 100 feet. The atoms
of the constituent molecules of water occupy the position H - O - H,
the bonds (-) indicating that the atoms are very close together; but
when the water is decomposed by an electric current, the atoms occupy
the positions O - O + H - H + H - H, the (+) indicating that the atoms
are relatively far apart from each other. Now the golf ball and the
earth, or the atoms of hydrogen and oxygen, are physically the same
material entities, whether they are close together or far apart, yet
when the earth and the ball, or the atoms of oxygen and hydrogen,
are separated from each other, their “properties” are different from
what they are when they are close together. What is it that makes
the difference? It is that which is _between_ them. Is it, in the
last case, “the potential energy of chemical affinity”? This dreadful
phrase is actually used in a recent book on biology: “In the elements
carbon and oxygen, so long as they remain separate, a certain amount
of energy remains latent. When the carbon and oxygen atoms are allowed
to come together and unite, this potential energy of chemical affinity
is liberated as kinetic energy.” What is changed by the tractation and
pellation (the terms suggested by Soddy in place of the anthropomorphic
ones, “attraction” and “repulsion”)? It is the ether which has become
changed in some way. Potential energy resides therefore in the ether of
space.
ISOTHERMAL AND ADIABATIC CHANGES
Let us consider the changes which occur in a gas under the influence
of changes in temperature and pressure, premising that the remarks
which we have to make can be applied to bodies in the liquid and solid
conditions, with some necessary modifications. A gas, then, consists
of a very great number of particles, or molecules, in motion. These
molecules move in straight lines at very high velocities, and if
the envelope in which the gas is contained is a restricted one, the
molecules collide with each other, and with the walls of the envelope;
and, being assumed perfectly elastic, they rebound from each other,
and from the walls of the vessel, with the same velocity which they
had when they collided. The pressure of the gas (say that of steam at
a temperature of 110° C., and a pressure of 120 lbs. to the square
inch in a steam boiler) is the sum of the impacts of the molecules
on the walls of the containing vessel. When the temperature is high
the molecules are moving at a higher mean velocity than when the
temperature is lower, and their mean free path tends to become greater.
The volume of a certain mass of gas, that is, the volume occupied by a
certain very great number of molecules, is greater the higher is the
temperature, provided the envelope is one capable of yielding. If we
reduce the capacity of the envelope in which the gas is contained, the
pressure will rise, for the intrinsic energy of the gas is still the
same; but we have done work on it, and by the law of conservation this
work, or at least the energy represented by it, must still exist. It is
represented by the decreased length of free path of the molecules, and
this means that the impacts on the walls of the vessel will be greater
than they were. There is, therefore, a certain relation between the
volume of a gas and its pressure, and this relation can be represented
by an equation involving the temperature, the pressure, and the volume.
[Illustration: FIG. 29.]
The diagram represents the pressure and the volume of a gas when these
things change. There are two conditions, (1) when the heat developed
by the compression is allowed to escape through the walls of the vessel
to the outside, or when the heat lost in the expansion of the gas is
compensated by the conduction of heat through the walls of the vessel
from outside; and (2) when the heat developed is retained in the gas,
as when the latter is contained in a vessel the walls of which do not
conduct heat. The pressure of the gas is measured along the horizontal
axis, and the volume is measured along the vertical axis, and a curve
is drawn so that for any value of the pressure there is a corresponding
value of the volume. Thus the values of the pressures _p_ and _p_↓{1}
in the diagram correspond to the value of the volume _v_. The curve
relating the change of pressure with a corresponding change of volume
is, in general, that called a rectangular hyperbola. But there are
two kinds of such curves: (1) that which we obtain by plotting the
corresponding values of pressure and volume, when the temperature
of the gas remains constant throughout the series of changes, that
is, when the rise of temperature which would occur when the gas is
compressed is compensated by the conduction of this heat to the outside
of the vessel containing the gas. Such a series of changes of pressure
and volume is called an _isothermal_ one. (2) When the heat developed
by the compression of the gas is retained in the gas, as when the walls
of the vessel in which these changes are effected are such as do not
conduct heat: such a series of changes is called an adiabatic one.
Adiabatic curves are steeper than are isothermal ones.
THE CARNOT ENGINE
This is an imaginary mechanism which performs a certain cycle
of operations. It does not really exist, but the conception of
its operation is of the greatest value in the consideration of
energy-transformations, and it is for this reason that we discuss it
here.
Consider a gas, or some other substance capable of expanding or
contracting. It contains intrinsic energy, and it is capable of doing
work. Thus, since a gas can expand indefinitely it can be made to do
mechanical work. A mass of gas at a pressure _p_↓{1}, and having a
volume _v_↓{1}, and at a temperature _T_°, can do work by expanding
till its pressure is reduced to _p_, and its volume increased to _v_.
If it expands adiabatically its temperature will fall to _t_°. Let us
suppose that _t_° is the temperature of the surrounding medium: the
gas cannot therefore cool further, and we can obtain no more work from
it. If the gas is the substance which we wish to employ as the working
substance in the Carnot engine, we must therefore bring it back to the
condition represented by _A_. That is, we must raise its temperature to
_T_°, we must reduce its volume to _v_↓{1}, and we must increase its
pressure to _p_↓{1}.
[Illustration: FIG. 30.]
Thus the steam of an engine is (say) at a temperature of 110° C., and a
pressure of 120 lbs. to the square inch. When it has passed through the
cylinder and condenser it is water at a temperature of, say, 15° C.,
and it is at atmospheric pressure. We must, therefore, bring it back to
its former condition by heating this water in the boiler till it is
steam under the former conditions of temperature and pressure.
Therefore we must, in order to obtain a self-acting engine, cause the
working substance, and the mechanism of the engine, to perform a series
of cyclical operations.
The Carnot engine is a cylinder containing a gas called the working
substance _S_, and this gas can be brought into thermal contact with a
source of heat, or a refrigerator, that is, the gas can be heated or
cooled by a mechanism outside itself. The walls of the cylinder are
made of some substance which is a perfect non-conductor of heat, but
the bottom of the cylinder is made of a substance which conducts heat
perfectly. There is a piston in the cylinder which fits it closely,
but which moves up and down without friction. At the bottom of the
latter is a valve which can be turned so as to place the bottom of the
cylinder, and therefore the gas, in thermal contact with a reservoir
of heat (+), or a refrigerator (-). But when the valve is turned so
that the non-conducting part _O_ fills the bottom, the gas is perfectly
insulated, and heat can neither enter nor leave it.
[Illustration: FIG. 31.]
Such an engine is, of course, an imaginary one, since there can be no
mechanism in which there is not a certain amount of friction between
moving parts, and there are no substances which conduct or insulate
heat perfectly. The engine is, in fact, the _limit_ to a series of
engines each of which is supposed to be more perfect than the last one.
It is a fiction which is of considerable use in theoretical work.
THE CARNOT POSITIVE CYCLE
We have therefore a substance which can be heated by contact with a
hot body, and which can then expand, doing mechanical work by raising
a piston, and perhaps turning a flywheel, and on which work is then
done so that it returns to its original condition. This is a cycle of
operations. If we consider only the changes which occur in the working
substance we can represent these changes by a diagram.
[Illustration: FIG. 32.]
_First operation_, (1→2). We suppose that the valve is turned so that
the non-conducting plug closes the cylinder. The piston is in the
position II (Fig. 31). Heat cannot then enter or leave the gas. But the
latter already contains heat: it is at a temperature of _T_↓{2}°, so
that it can expand doing work. Let it expand, forcing up the piston.
During this operation the pressure of the gas will fall from a point
on the vertical axis opposite 1 to a point opposite 2, and its volume
will increase from a point on the horizontal axis beneath 1 to a point
beneath 2. It will cool because it has expanded, and no heat is allowed
to enter it during this act of expansion. The expansion is therefore
adiabatic; the temperature falls from _T_↓{2}° to _T_↓{1}°; and work is
done _by_ the gas.
_Second operation_, (2→3). The piston is now at the position I, that
is, at the upper end of its stroke, and we must bring it back again
to the lower end of the cylinder. The valve is turned so that the
bottom of the cylinder is placed in thermal communication with the
refrigerator (-), and the piston is pushed in to the position II. The
gas is therefore compressed until its volume decreases from a point
beneath 2 to a point beneath 3. As it is being compressed, heat is
generated and its temperature would rise, but as this heat is generated
it flows into the refrigerator, so that the temperature of the gas
remains the same during the operation. The contraction is therefore an
isothermal one; the temperature remains at _T_↓{1}°; and work is done
on the gas from outside.
_Third operation_, (3→4). But the piston is not at the lower end of
its stroke yet. We turn the valve so that the bottom of the cylinder
is closed by the non-conducting plug _O_, and then push in the piston
until it reaches the position III. The gas is still further compressed,
and this compression generates heat. But the heat cannot escape, so
that the temperature of the gas rises until it reaches _T_↓{2}°. The
contraction is therefore an adiabatic one. Work is done _on_ the gas.
_Fourth operation_, (4→1). The piston is now at the lower end of its
stroke. We turn the valve so that the bottom of the cylinder is placed
in communication with the source of heat (+). The gas expands from
the point beneath 4 to the point beneath 1, raising the piston to the
position II. This expansion of the gas would lower its temperature,
but it is in communication with the source of heat, and so it does
not cool, but draws heat from the source and remains at a constant
temperature, _T_↓{2}°. The expansion is therefore an isothermal one.
Work is done _by_ the gas.
This completes the cycle. But the gas is heated, and when the piston
is at position II, the valve is turned so as to close the cylinder by
the non-conducting plug _O_. The heat already contained in the gas
continues to expand, the latter doing more work, but this expansion
causes the temperature to fall from _T_↓{2}° to _T_↓{1}°. This is the
operation with which the cycle commenced.
Summarising the positive Carnot cycle, we see that the engine takes
heat from a source (+) and gives up part of this to a refrigerator (-),
(in an actual steam-engine heat is taken from the boiler and given up
to the condenser water). If we measure the quantity of heat taken from
the boiler in the steam which enters the cylinders we shall find that
this quantity of heat is greater than the quantity which is given up
to the condenser water. What becomes of the balance? It is converted
into the mechanical work of the engine. The Carnot engine therefore
takes a quantity of heat, _Q_↓{2}, from the source and gives up another
quantity of heat, _Q_↓{1}, to the refrigerator. We find that _Q_↓{2} is
greater than _Q_↓{1} and the balance, _Q_↓{2} - _Q_↓{1}, is represented
by the work done by the engine. Heat-energy falls from a state of high,
to a state of low potential, and is partly transformed into mechanical
work.
THE CARNOT NEGATIVE CYCLE
This is simply the positive cycle _reversed_. The reader should puzzle
it out for himself if he is not already familiar with it. It consists
of an adiabatic contraction 2→1, an isothermal contraction 1→4, an
adiabatic expansion 4→3, and an isothermal expansion 3→2. A quantity
of heat, _Q_↓{1}, is taken from the refrigerator at a temperature
_T_↓{1}°, and another quantity, _Q_↓{2}, is given up to the source at
a temperature _T_↓{2}°. But _Q_↓{2} is greater than _Q_↓{1}, and the
engine therefore gives up more heat than it receives, while, further,
heat flows from a body at a low temperature to another body at a higher
temperature. Where does the engine get this energy from? It gets it
because work is done _upon_ it by means of an outside agency, and all
of this work is converted into heat.
REVERSIBILITY
The Carnot engine and cycle are therefore perfectly reversible. Not
only can the engine turn heat into work, but it can turn work into
heat. This perfect, quantitative reversibility is, however, a property
of the imaginary mechanism only, and it does not exist in any actual
engine.
ENTROPY
Let us consider the cycle more closely. In the operation 4→1, which
is an isothermal expansion, there is a flow of heat-energy from the
source and a transformation of energy into work. The gas in the
condition represented by the point 4 had a certain pressure and a
certain volume. In the condition represented by the point 1, its
pressure has decreased, its volume has increased, and its temperature
is the same. Its physical condition has been changed, and to bring
it back into its former condition something must be done to it. Let,
then, the gas continue to expand without receiving any more heat, or
parting with any: that is, let it undergo the adiabatic expansion 1→2
until its temperature falls to that of the refrigerator, _T_↓{1}°. We
now compress the gas while keeping it at this temperature, that is,
we cause it to undergo the isothermal contraction 2→3, during which
operation it is giving up heat to the refrigerator, so that there is
again a flow of heat-energy. We then compress it still further without
allowing heat to escape from it, that is, we cause it to undergo the
adiabatic contraction 3→4. During this operation the gas rises in
temperature to _T_↓{2}°. It is now in the condition that it was when
the cycle commenced.
In this cycle of operations heat first entered, and then left the gas,
and with this entrance or rejection of heat, the condition of the
gas with respect to its power of doing work changed. We investigate
this flow of heat, and the concomitant change of properties of the
substance, with regard to which the flow took place, by forming the
concept called _entropy_. We make the convention that when heat enters
a substance the entropy of the latter increases, and when heat leaves
it its entropy decreases. We call the quantity of heat entering or
leaving a substance _Q_, and the temperature of the substance _T_. Then
_Q_/_T_ is proportional to the change of entropy of the substance when
the quantity of heat, _Q_, enters or leaves it.
Now it is a fact of our experience that heat can only flow, _of
itself_, from a hotter to a colder body. Consider two such bodies
forming an isolated system, the temperature of the hotter one being
_T_↓{2}°, and that of the colder one _T_↓{1}°. Let _Q_ units of heat
flow from the body at _T_↓{2}° to that at _T_↓{1}° no work being done.
Then the loss of entropy of the hotter body is _Q_/_T_↓{2}°, and the
gain of entropy of the colder body is _Q_/_T_↓{1}°. The nett change of
entropy of the system is _Q_/_T_↓{1}° - _Q_/_T_↓{2}°. Since _T_↓{2}°
is greater than _T_↓{1}°, _Q_/_T_↓{2}° is less than _Q_/_T_↓{1}°.
Therefore the expression _Q_/_T_↓{1}° - _Q_/_T_↓{2}° is positive,
that is, the entropy of the system, as a whole, has increased. When
heat flows from a hotter to a colder body the nett entropy of the two
bodies, therefore, increases.
But we can also cause heat to flow from a colder to a hotter body _by
effecting a compensatory energy-transformation_. Such a compensation
would not occur by itself in any system capable of effecting an
energy-transformation, if it is to be effected some external agency
must act on the transforming system. We can suppose it to happen in
a perfectly reversible imaginary mechanism. Suppose a Carnot engine
works in the positive direction, taking heat from a reservoir at
temperature _T_↓{2}°, and giving up part of this heat to a refrigerator
at _T_↓{1}°, and doing a certain amount of work _W_. Suppose that
this work is stored up, so to speak, say by raising a heavy weight,
which can then fall and actuate the same Carnot engine in the opposite
(negative) direction. The engine then exactly reverses its former
series of operations. The work it did is reconverted into heat, and as
much of this heat flows from the refrigerator into the source, that
is, from a colder to a hotter body, in the negative operations, as
flowed from the source to the refrigerator in the positive operations.
In this primary energy-transformation, combined with a compensatory
energy-transformation, there is no change of entropy. The mechanism is
an ideal one--the limit to an irreversible mechanism.
But--and now we appeal to experience and cease to work with ideal
mechanisms--the actual engine which we can design and work is one
in which there will be friction, in which some parts will conduct
heat imperfectly, and other parts will insulate heat imperfectly.
Let the friction generate _q_ units of heat, and let the quantity
of heat which is “wasted” by imperfect conduction and insulation
be _q_↓{1}. This heat will flow into the refrigerator, or will be
radiated or conducted to the surrounding medium, which we suppose to
be at the same temperature as the refrigerator. If, then, we divide
this total quantity of heat by the temperature _T_↓{1}°, we get (_q_
+ _q_↓{1})/_T_↓{1}° = _S_↓{1} as the quantity of entropy which is
generated as the result of the imperfections of the engine, in addition
to the quantity of entropy, _S_, which would be generated if the engine
were a perfect one. Both _S_ and _S_↓{1}_ are positive.
Also in the working of the engine in the negative direction a certain
quantity of entropy, _S_↓{1}, is generated for reasons similar to those
mentioned above.
The entropy generated when the engine works in the positive direction
is therefore _S_ + _S_↓{1}, and when it works negatively the quantity
generated is also _S_↓{1}. The entropy destroyed when the engine works
negatively is _S_. The total change of entropy is therefore 2_S_↓{1}
+ _S_ - _S_, that is, 2_S_↓{1}. In an actual energy-transformation
combined with a compensatory energy-transformation there is therefore
an increase of entropy.
We can generalise these statements so that they will apply
not only to a heat-engine but to all mechanisms which effect
energy-transformations. In all such transformations entropy is
generated. Therefore _the Entropy of the Universe tends to a maximum_.
AVAILABLE AND UNAVAILABLE ENERGY
Consider the Carnot engine as a perfect mechanism. It takes heat-energy
from a source at a temperature _T_↓{2}°, and it gives up heat to a
refrigerator at a temperature _T_↓{1}°_, _T_↓{2}° being greater than
_T_↓{1}°. In the adiabatic expansion 1→2 the gas continues to expand
until its temperature becomes equal to that of the refrigerator. It
cannot, then, expand and do work any longer, and thus the proportion
of the heat, _Q_↓{2}, received from the source, which can be converted
into work, depends on the difference of temperature _T_↓{2}° -
_T_↓{1}°. The greater is this difference the greater will be the
proportion of the heat-energy received which can be converted into
work. If the engine were a perfect one, and if the gas were also a
perfect one (that is a gas which would continue to expand according
to the equation for the adiabatic expansion of gases), and if the
refrigerator were absolutely cold, then _all_ the heat energy received
from the source could be converted into work.
We cannot produce a refrigerator of absolute temperature 0°, and
therefore only a certain proportion of the heat which is received by
the engine can be transformed into mechanical work. But this work can
be used to reverse the action of the engine, and thus the same fraction
of the total heat-energy which was given to the refrigerator can be
taken from it and given back to the source. The perfect engine is
therefore reversible without loss of available energy.
Now consider still the engine as a mechanism which takes heat from a
source and gives it to a refrigerator, but let it be an actual engine.
Instead of giving up a certain fraction of the heat received to the
refrigerator--a fraction equal to _Q_↓{1} (_T_↓{1}°/_T_↓{2}°), it
gives up rather more, because it is not a perfect mechanism, that is,
it generates friction, etc. Some of the heat received thus ceases
to be available for the performance of work; and passes into the
refrigerator. The fraction of the heat-energy which passes into the
refrigerator in the perfectly reversible engine was unavailable energy
in the conditions in which the mechanism worked, or was imagined to
work, but in the actual engine this fraction is increased. If we
divide the increase of unavailable energy by the temperature of the
refrigerator, the product is the increase of entropy generated in the
actual engine over that generated in the ideal engine. Because of this
reduction of available energy the actual engine is an irreversible
mechanism.
This is the connection between unavailable energy and entropy. In all
transformations some fraction of the transforming energy becomes heat,
and this heat flows by conduction and radiation into the surrounding
bodies. In general this heat simply raises the temperature of the
medium into which it flows, and becomes unavailable for further
transformations. With every transformation that occurs some part of the
energy involved becomes unavailable. Therefore although the sum of the
available and unavailable energy of the Universe remains constant, the
fraction of unavailable energy tends continually to a maximum.
INERT MATTER
We can see now what is indicated by Bergson’s “inert matter.” It is not
matter deprived of energy--such an expression has no meaning--_it is
energy which is unavailable for further transformations_.
The matter in which we choose to say that this energy is inherent has
become _inert_. Let us substitute for the Carnot engine the actual
steam-engine of a ship, the condenser of which is cooled by the sea
water which is taken in, and which is then heated and flows out again
into the sea. The heat derived from the source, that is, from the
furnace of the boiler where coal is burned to raise steam, thus passes
out into the sea. Now the heat capacity of the sea is so great that the
temperature of the water is not appreciably raised by this heat, which
drains into it from the engine: even if it were appreciably raised, the
heat would be conducted into the earth, or would be radiated out into
space, and would then raise the temperature of the material bodies of
the universe. But let all this heat remain in the sea. It then simply
raises the temperature of the water by an exceedingly small amount,
and the motions of the molecules become infinitesimally increased.
But the heat becomes equally distributed by conduction and convection
throughout the mass of the water in the sea, and as there are no
differences in adjacent parts there are no means whereby the energy
which thus passes into the sea can be again transformed.
A new order of things is the result of the processes we have indicated.
The segregated, available heat-energy of material bodies has become
transferred to the un-co-ordinated, diffuse, unavailable energies of
the molecules which compose these bodies. The transformations which we
can effect depend on the condition that the energy which we utilise
is that of aggregates of molecules which are in a different physical
condition, as regards this energy, from adjacent aggregates. But when
this energy becomes equally distributed among the molecules of all the
aggregates, the matter in which it inheres becomes inert. If we could,
by a sorting process like that of Maxwell’s hypothetical demons, a
process which does not expend the energy with which it deals, separate
the molecules which were moving slowly from those which were moving
more quickly, we could make this energy again available. But it must
clearly be understood that our physics is the physics not of individual
molecules, but of aggregates of molecules.
INDEX
Absolute, Driesch’s theory of, 47.
Acceleration (in physics), 355.
Acquired characters induced by the environment, 216;
a means of transformism, 220;
evidence of transmission scanty, 225;
transmission not inconceivable, 226.
Actions, categories of, and consciousness, 282;
deliberative, 283;
mechanistic hypothesis of, 157;
stereotyped, 283;
at a distance, 304.
Activation of the ovum, 176.
Adaptability, indicative of dominance, 258.
Adaptation, 217;
and acquired characters, 219;
and changes of morphology and function, 219;
not inherited, 220;
causes of, 239.
Adaptive response, 219.
Adiabatic changes, 361.
Aggregates, molecular, 353.
Algæ, distribution of, 260.
Allelomorphs, Mendelian, 231.
Alternation of generations, 175.
Amido-substances, 88.
Anabolism, 88.
Anatomical parts, homologies of, 251.
Animal action, considered objectively, 278.
Animal and plant contrasted, 269.
Animality, 269.
Annectant forms of life, 253.
Annelids, morphology of, 248.
Anthropomorphism in theories of action, 148.
Anti-enzymes, 94.
Antitoxins, 36.
Ants, a dominant group, 260.
Appendix vermiformis, 250.
Approximation, standards of, 347.
Armoured animals, 263.
Arthropods, morphology of, 249;
a dominant group, 259;
distribution, 260;
musculature of, 275;
adaptations for mobility, 275;
limits to size of, 275.
Assimilation, 67.
Atoms, constitution of, 355;
arrangements of, 353.
Automatism of animals deduced from mechanistic theories, 280.
Autonomy in development, 322.
Available energy, 62;
and entropy, 374.
Bacteria, a dominant group, 259;
distribution, 259;
geological history, 259, 261;
morphology, 268;
metabolism, 266;
specialisation, 263;
parasitism, 259;
nitrogen, 73;
prototrophic, 119, 266;
paratrophic, 266;
putrefactive, 266;
fermentation, 266;
and Brownian movements, 119;
compensatory to plants, 267.
Bergson, 28;
creative evolution, 244;
duration, 154;
animals and plants, 78;
eye of Pecten, 234;
inert matter, 375;
infinitesimal analysis of the organism, 111;
kinematographic analysis, 110;
theory of intellectualism, 51;
memory, 156;
morphological themes, 250;
theory of pain, 281;
theory of perception, 7, 10;
the vital impetus, 318.
Biology, systematic, 201, 203.
Biophors, 132;
size of, 183;
growth of, 185.
Biotic energy, 325.
Borelli and animal mechanism, 125.
Brownian movement, 118;
significance of, 119.
Bryan and thermodynamics, 62.
Bud-formation, 165.
Calculus, infinitesimal, 25, 115, 350.
Calorimetric experiments, 65, 68.
Capacity-energy factors, 61.
Carnot’s cycle, 69, 78, 113;
negative, 368;
description of, 363, 366;
compared with plant metabolism, 75;
compared with the organism, 73.
Catalysis, 90;
universality of, 91.
Catalysts, characters of, 91.
Categories of organisms, 209.
Central nervous system, specialisation of, 273;
a switchboard, 273;
evolution of, parallel with evolution of muscular system, 281.
Chance in evolution, 237.
Chemical affinity, 361.
Chemical energy, degradation of, 75.
Chemical reactions, direction of, 78;
exothermic, 86;
explosive, 86;
similar in organic and inorganic systems, 78.
Chemical synthesis, involve vital activity, 318.
Chemistry, medieval, 125.
Chlorophyll, 69.
Chlorophyllian organisms, 88;
metabolism of, 265;
a dominant group, 259;
essential morphology of, 268;
distribution of, 260.
Chromatin of the nucleus, 130;
the material basis of inheritance, 182.
Chromosomes, 130, 182, 183.
Classification of organisms, 209.
Classificatory systems, are artificial arrangements, 289;
suggest evolutionary process, 210.
Clausius, 54;
and Carnot’s Law, 113.
Cœlenterates, morphology of, 248.
Cœlomate animals, 256.
Colloidal platinum, 91.
Colloids, 107.
Colonial organisms, 164.
Comparative anatomy, task of, 251.
Compensatory energy-transformations effected by life, 309.
Conjugation, 173;
and heredity, 176;
a stimulus to growth, 175.
Consciousness involves analysis of the environment, 11;
analysis of, is an arbitrary process, 12;
a feeling of normality, 6;
a part of crude sensation, 40;
simplified by reasoning, 41;
an intensive multiplicity, 303;
degree of, is parallel to development of sensori-motor system, 280;
not existent outside ourselves, 278;
not a function of chemico-physical mechanism, 160;
intense in difficultly performed operations, 281;
and activity of cerebral cortex, 281;
absent in parasites, 291.
Conservation a test of reality, 357.
Conservation of energy, 52;
in organisms, 83.
Conservation of structure, 253, 256.
Constants, mathematical, 344.
Continuity of cells in embryo, 171.
Contractility, 100;
muscular, 103.
Co-ordinates, systems of, 23.
Corals, 164.
Cosmic evolution, 314;
is a tendency towards degradation of energy, 316.
Creation, special, 214.
Curvature, 27.
Curves, isothermal and adiabatic, 362.
Cuttle-fishes, 250.
Cytoplasm, 130.
Darwin, and natural selection, 221;
acquired characters are inherited, 220;
hypothesis of pangenesis, 181.
Death, is catastrophic katabolism, 340.
Degradation of energy, 81.
Deliberation and consciousness, 281.
Demons, Maxwell’s, 116.
Descartes and mechanism, 121;
the rational soul, 123, 318;
his physiology, 122;
his spiritualism, 124;
and animal automatism, 125.
Descent, collateral, 257.
Determinants in embryology, 132, 183;
arrangement of, 184;
latent in regenerative processes, 142.
Development, organisation in, 128;
parthenogenetic, 176;
reverses inorganic tendencies, 324;
impossibility of chemical hypotheses, 141;
is the assumption of a mosaic structure, 301;
blastula stage in, 129;
gastrula stage in, 130;
pluteus stage in, 140;
individual, 300.
Developmental systems prospective value of, 138;
prospective potency of, 138.
Diatoms, 163;
distribution of, 260.
Differential elements, 115.
Differentiation in development, 170.
Diffusion in the animal body, 95.
Digestion, 67;
chemistry of, 72.
Dinosaurs, an unsuccessful line of evolution, 275.
Dissipation of energy, 114;
in physical mechanisms, 59;
by the organism, 68, 79.
Distribution of organisms, 262;
limits to, 259;
indicative of dominance, 258.
Diversity, physical, 54;
effective and ineffective, 115.
Dominance in geological time, 258;
implies long geological history, 261;
Mendelian, 196.
Dominant organisms, 258, 259, 264.
Driesch natural selection, 229;
analytical definition of the organism, 331;
entelechy, 318;
experimental embryology, 134;
historical basis of reacting, 154;
logical proof of vitalism, 136;
proof of vitalism from behaviour, 153;
theory of the absolute, 47.
Duration, 28;
duration and time illustrated, 30;
illustrated by immunity, 35;
more than memory, 155;
a factor in responding, 155.
Ecdysis, 276.
Echinoderms, morphology of, 248.
Ectoderm, 177.
Effector organs, 158, 271.
_Élan vital_, 161.
Electromagnetism, 355.
Electrons, 304, 355.
Elimination, natural, 229.
Embryological stages compared with physical phases, 308.
Embryology, 127;
hypotheses of, 128;
physical hypotheses fail, 128;
experimental, 128;
suggests phylogenetic history, 213.
Emulsoids, 108.
Endoskeleton, 177, 276.
Energetics, first law of, 51;
second law of, 113.
Energy, 356;
available and unavailable, 55;
biotic, 325;
chemical, 61;
and causation, 54;
degradation of, 63;
dissipation of, 53;
electrical, 61;
forms of, 325;
kinetic, 52, 357;
mechanical, 60, 61;
potential, 53, 358;
of position, 360.
Energy-transformations, 54, 371;
anabolic, 89;
in the animal, 70;
compensatory, 88;
compensatory organic, 268;
irreversible, 59;
in physical mechanisms, 58;
in the plant, 71.
Engelmann, and the artificial muscle, 105.
Entelechy, 161, 318;
not energy, 329;
is power of direction, 329;
not spatial but acts into space, 330;
an intensive manifoldness, 330;
is arrangement, 323;
involves regulations, 323;
arrests inorganic happening, 327;
initiates chemical happening, 327;
compared with enzyme action, 327;
illustrated by analogy, 322.
Entropy, 54;
augmentation of, 75;
and Carnot engine, 369.
Environment, does not select variations, 235;
made by the organism, 236.
Enzymes, 90;
nature of, 92;
pancreatic, 93;
reversible, 93;
activation of, 92.
Enzyme activity, 93.
Epigenesis in development, 129.
Equilibrium, chemical, 102.
false, 86, 151.
Ether of space, 46, 304, 361;
potential energy resides in, 361.
Evolution tendencies of, 252, 264, 276, 295;
separation of tendencies, 296;
a transformation of intensive into extensive manifoldness, 309;
a dissociation of tendencies originally coalescent, 305;
increases diversity, 310;
segregates energy, 311;
compared with permutations and combinations, 301;
a series of phases in a transforming system, 298;
a logical hypothesis, 214;
parallel processes in, 234;
geological time inadequate for, 237;
side paths in, 262;
mechanistic hypotheses inadequate, 237;
cosmic, 214, 297, 314;
of the crust of the earth, 264.
Excretory products, 269.
Exoskeleton, 276.
Exothermic reactions, 86.
Experience and duration, 156.
Experimental biology proves evolution, 246.
Explosive reactions, 101.
Extension in space, 18.
Extinct groups, 263.
Fats, digestion of, 93.
Fecundity of animals, 179, 239.
Ferments, 92.
Fertilisation (in reproduction), 176.
Finalism, 216.
Fishes, distribution of, 261.
Fluctuating variations, 200.
Food-stuffs, absorption of, 89.
Force, 354.
Form, accidental and essential, 167, 353;
geological, 168;
crystalline, 168.
Frequency distributions, 22, 187, 350.
Frog, development of egg of, 131.
Functionality, 343;
in physical systems, 307.
Galvanotropism, 145.
Gases, compression of, 362;
kinetic theory of, 117, 361.
Gastrea-theory, 177;
illustrated, 255;
limitations of, 256.
Genera, stability of, 186.
Geometry, Cartesian, 25;
Euclidean, 19, 25;
perceptual and conceptual limits, 21.
Geotropism, 144.
Germ-cells, 175;
and soma, 179.
Germinal selection, 241.
Germ-layers, 177;
theory of, 256.
Germ-plasm, a mixture, 240;
stability of, 240.
Givenness, 47.
Gonads, 179.
Growth law of, in the organism, 172;
by accretion, 169;
by ecdysis, 276;
geometrical, 169;
physical, 167;
of crystals, 167;
and differentiation, 170;
variability of, 172.
Haeckel, the Gastrea-Theorie, 177, 254.
Harmonic analysis, 11.
Harvey, and the circulation of the blood, 121.
Heat, flow of, 117;
production of, in physical changes, 114.
Heliotropism, 144.
Heredity, 181.
Hertzian waves, 355.
Homoiothermic animals, 67.
Hormones, 225.
Human activity, tends to arrest dissipation of energy, 312.
Huxley, 84;
and mechanistic biology, 127;
and the physical basis of life, 113;
and mechanism, 106;
and universal mathematics, 215.
Hybrids, Mendelian, 196;
infertility of, 195;
between Linnean species, 194.
Hydra, regeneration of, 162.
Idants, 183.
Idealism founded on pure reasoning, 45;
of Berkeley, 45.
Ids, 183.
Immunity, 35.
Individual, 162;
definition of, 167.
Individuality, orders of, 163;
physical concept of, 165;
morphologically an artificial concept, 166;
in societies, 171.
Inertia, 354.
Infinity, a definition of, 342.
Inorganic happening abolishes diversity, 310.
Instinct, a problem for naturalists, 283;
an inheritable adaptation of behaviour, 287.
Instinct and intelligence, 283;
distinction not absolute, 294;
may coexist, 306.
Instinct and functioning, 286.
Instinctive actions not necessarily unconscious, 283;
not learned, 286;
not necessarily perfect, 284;
effective from the first, 285;
capable of improvement, 285.
Intelligent actions, non-inheritable adaptations of behaviour, 287;
involve deliberation, 50, 287;
involve conscious relations with the environment, 288;
involve use of tools, 284.
Intensity-factors, 61.
Intensive multiplicity, 303.
Irreversibility, 62.
Irritability, 100.
Isothermal changes, 361.
James, William (and academic philosophies), 80.
Jennings, and physiological states, 154;
behaviour of Protozoa, 293;
animal movements, 149;
the avoiding reaction, 149.
Katabolism, 90.
Kinases, 92.
Kinematographic analysis, 316.
Lamarck, hypotheses of evolution, 220.
Lamarckian inheritance, an inadequate cause of transformism, 227.
Lankester, acquired characters not inherited, 221.
Laplace, and universal mathematics, 215.
Laplacian mind, 299.
Larval stages, 170.
Latency (of characters), 195.
Lavoisier, and chemistry of the organism, 127.
Life and adaptation to physical conditions, 338;
and reversibility, 339;
a direction of energies, 341;
defined energetically, 337;
cosmic origin of, 338;
physical conditions for, 338;
limited in power, 306;
sparsity of, on the earth, 306;
tends to arrest dissipation of energy, 314;
its origin a pseudo-problem, 337.
Life-substance, the primitive, 301.
Locomotion, 258.
Loeb and the associative memory, 155;
and artificial parthenogenesis, 176;
mechanism and life, 127;
stereotropism, 19;
theory of tropisms, 144;
tropistic movements, 146;
theories of heredity, 181.
Limit, the mathematical, 346.
Limits to perceptual activity, 23.
Links, missing, 252.
Linnean species, 201.
Manifoldness, intensive, 302.
Mass, 353.
Mass action, 140.
Materialism, 85.
Mathematics, evades consideration of time, 35.
Matter, 353;
inert, 375;
notion of is an intuitive one, 352.
Maxwell, and sorting demons, 116, 377.
Mayow, and chemical physiology, 126.
Mechanical work, done by the animal, 67;
not done by the plant, 71.
Mechanism, organic and inorganic, 78;
the thermodynamic, 66;
radical, 215;
in life, 121.
Membranes, semi-permeable, 95.
Memory, 39;
a possible cerebral mechanism of, 158;
mechanistic hypotheses impossible, 157.
Mendelism, 196;
a logical hypothesis, 199;
terminology is a symbolism, 198;
analogy of unit characters with chemical radicles, 197;
transmission of characters of, 230.
Mesoderm, 177;
origin of, 255.
Metabolism, 37, 88, 209;
analytic, 269;
of animals, 65, 67;
constructive, 269;
destructive, 269;
direction of, 69;
in green plant, 70, 75;
intra-cellular, 99;
integration of its activities, 111;
rôle of oxygen in, 105;
specialisation of during evolution, 305;
synthetic, 269.
Metaphysics of science, 45.
Metazoan animals, 162.
Mitosis, 182.
Mobility, organic, 269;
structural adaptations tending to, 275.
Modifications of structure adaptive and non-adaptive, 251.
Molecules, 353;
size of, 116;
in a gas, 115;
aggregations of, 108.
Molluscs, morphology of, 249.
Morgan, and physico-chemical mechanisms, 128, 143.
Morphogenesis, 257.
Morphological evolution, tendencies of, 295.
Morphological structures degeneration of, 251;
suppression of, 250;
coalescence of, 250;
replacement of, 250;
specialisation of, 250;
change of function of, 251.
Morphology, 209;
a basis of classification, 210;
relates groups of organisms, 211;
distinctions of, not absolute, 285, 290;
generalised, 250;
suggests blood relationships, 213;
schemata of, 249, 291;
cannot be considered apart from physiology, 285.
Mosaic-theory of development, 131.
Motion not an intellectual concept, 27;
not considered in Euclidean or Cartesian geometry, 26;
bodily motion is absolute, 24;
outside ourselves is relative, 24.
Motor-habits, 38, 155.
Multicellular organisms, evolution of, 223.
Muscular contraction, 104;
metabolism in, 104;
heat production in, 104.
Muscular and nervous organs, 275.
Musculature and weight of body, 275.
Mutations, 189;
essential nature of, 193;
causes of, 200;
must be co-ordinated, 231;
physical model of, 192;
the material for selection, 230.
Nägeli, and autonomy in development, 160.
Natural selection, 228;
generality of, 229;
a slow process, 230.
Nebulæ, 315.
Nebular hypothesis, 296.
Nerve impulses, 100;
velocity of, 101;
integration of, 273.
Nervous system, 272;
in co-ordination of activities, 171;
paths in, 157.
Nervous activity, 107;
metabolism in, 107;
electric changes in, 107;
influence of metabolism on, 97.
Nothing, a pseudo-idea, 18.
Nucleus, evolution of, 222;
division of, 130, 182.
Ontogenetic stages, 255.
Orders of individuality, 171.
Organism, definition of, 331;
analysis of its activities, 109;
animal and plant, 76;
considered energetically, 77;
the dominant, 258;
a function of the environment, 216;
a mechanism, 51;
the primitive, 222;
a physico-chemical system, 65;
a thermodynamic mechanism, 104.
Organic chemical syntheses, 317.
Organisation in development, 137.
Organ-rudiments, 257.
Osmosis, 95, 99.
Ostracoderms, 291.
Ostwald on catalysis, 91.
Ovum, development of, 129;
maturation of, 198, 239;
an intensive manifoldness, 302.
Oxidases, 105.
Oxygen in metabolism, 69.
Pain, Bergson on, 281.
Palæontology, 210;
relates groups of organisms, 211.
Pangenesis, 181.
Paramœcium, division of, 173, 175;
responses of, 4.
Parasitism, 259;
tends to immobility, 290.
Parthenogenesis, 176;
artificial, 176.
Particles, 356.
Pecten, eye of, 233.
Perception
not merely physical stimulation, 7;
involves effector activity, 7;
involves deliberative action, 9;
arises from acting, 50;
and choice of response, 155;
is unfamiliar cerebral activity, 8;
skeletonises consciousness, 40.
Peridinians, 77, 163;
distribution of, 260.
Personal equation, 45.
Personality, 167;
an intuition, 167;
division of, 173;
is absolute, 48.
Pflüger, and experimental embryology, 131.
Phases in physical systems and organic systems, 321;
in transforming systems, 308.
Phenomenalism, 46.
Photosynthesis, 70, 76, 86.
Phototaxis, 144.
Phyla
animal, 247;
morphology of, 247;
relations between, 252;
ancestries of, 252.
Phylogenies, 253;
are summaries of morphological results, 254;
indicative of directions of evolution, 254;
criteria of, 253.
Phylogeny, 246.
Phylum, 210.
Physical basis of life, 84.
Physico-chemical reactions, 80;
are directed, 118;
the means of development and behaviour in the organism, 160.
Physico-psychical parallelism, 160.
Physics, a statistical science, 116, 377.
Physiology
Galenic, 122;
an analysis of organic activity, 120, 328.
Plants, geological history of, 261;
characterised by immobility, 277;
contrasted with animals, 277.
Platonic ideas, 204.
Platyhelminths, morphology of, 248.
Poikilothermic animals, 68.
Poincaré, and Brownian movement, 119.
Polar bodies, 198.
Polyzoa, 164.
Porifera, 248.
Potential, 61.
Potential energy, 58, 114.
Preformation an embryological hypothesis, 128.
Probability, 350.
Proteids, digestion of, 90.
Proto-forms, 254.
Protoplasm, nature of, 106;
artificial, 106;
disintegration of, 107;
activities of, 107;
similar in plant and animal, 294.
Protozoa, 247;
behaviour of, 293.
Pterodactyls, 274.
Races (in specific groups), 194.
Radiation, 355;
of sun, 51;
transformation of energy of, 57.
Radio-activity, 56, 359.
Reality, objective, 43.
Reception, 3;
organs of, 271;
by specialised sense-organs, 11.
Recessiveness, Mendelian, 196.
Reflex action, 4, 272;
concatenated, 150;
a complex series of actions, 6;
not necessarily accompanied by perception, 155;
the basis of instincts, 150;
a schematic description, 5;
in decapitated frog, 6;
frictionless cerebral activity, 8;
involves a limited part of the environment, 50.
Reflex arcs, 272.
Regeneration, 142;
in Hydra, 164;
in sea-urchin embryo, 164;
in Planaria, 164.
Regression, 189.
Reinke, and structure of protoplasm, 106.
Reintegration in development, 171.
Rejuvenescence, 175.
Releasing agencies, 157.
Reproduction, 167;
asexual, 175;
by brood-formation, 173;
by conjugation, 173;
sexual, 174;
by division, 172;
compared with minting machine, 242;
of the tissues, 180.
Responses of organisms, 217;
directed, 269;
of magnet, 279;
of green plant, 279.
Reversibility, physical, 369.
Rodewald, chemical nature of protoplasm, 106.
Roux, experimental embryology, 131;
development the production of a visible manifoldness, 307.
Saliva, secretion of, 96.
Salivary glands, metabolism of, 96.
Salivary secretion, not a purely mechanistic process, 112.
Sea, not really rich in life, 306.
Sea-urchin gastrula, 170.
Secretion described mechanistically, 98.
Secretion, psychical, 99.
Segmentation of the ovum, 129.
Selection, natural, 228;
from fluctuating variations, 189;
from mutations, 190.
Semon, mnemic hypothesis of heredity, 181.
Senescence, 175.
Sensation, 2;
analysis of, 13.
Sense-receptors and the idea of matter, 352.
Sensori-motor system, 270;
dominant in animals, 271, 273;
specialisation of, 271, 273;
essentially the same in all animals, 294;
absent in plants, 269;
vestigial in some parasites, 290.
Sexuality, 174.
Siphonophores, regeneration in, 163.
Size of animals, 274.
Skeleton of vertebrates, 276;
of arthropods, 276;
and mobility, 276.
Soddy, and chemical energy, 361.
Soma, 179;
evolution of, 223.
Space, form of, 18;
3-dimensional, 18;
3-dimensional space an intuition, 19;
2-dimensional, 19;
the form of, depends on modes of activity, 21, 25.
Species, are categories of structure, 201;
comparison with Platonic ideas, 204;
criteria of, 202;
elementary, 193;
are intellectual constructions, 203;
individuality of, 203;
Linnean, 201, 289;
are phases in an evolutionary flux, 206;
are families in the human sense, 208;
systematic, 201.
Specific organisation, stability of, 186.
Stahl, and the phlogistic hypothesis, 126;
and vitalism, 126.
Stimuli, elemental, 151;
physico-chemical, 151;
formative, 176;
complex auditory, 152;
integration of, 152;
individualised, 152, 270;
contractile, 103.
Stimulus and response, functionality of, 152.
Substantia physica, 46, 355.
Surface tension, 105, 106.
Suspensoids, 108.
Sylvius, the organism a chemical mechanism, 125.
Symbiosis, 77.
Symbiotic organisms, 88.
Synapses, in central nervous system, 158, 272.
Synthetic chemistry, 236, 317.
System, isolated, 63.
Systems in development
equipotential, 139;
harmonious equipotential, 139;
complex equipotential, 140.
Taxis, 144;
no perception in, 155.
Telegraphy, wireless, 355.
Temperature of sun, 56;
of space, 57.
Thermodynamics, 51;
1st law of, 51;
2nd law of, 54, 63, 309, 316;
and Maxwell’s demons, 118;
laws of subject to limitations, 115.
Thermodynamical mechanism, the organism not a, 69.
Thomson, W., dissipation of energy, 113.
Time a series of standard events, 28;
astronomical, 34;
time differentials, 34.
Tissues, evolution of, 223.
Tools, nature of, 285;
use of must be learned, 285;
bodily, 285.
Toxins, 36.
Transformism, 213.
Trematodes, larval stages of, 165.
Trial and error, 293;
in reasoning, 293;
a hypothesis of animal movements, 150.
Trigger reactions, 87.
Trilobites, an ancient group, 261.
Tropisms, 144;
in plants, 269, 279;
in moths, 280;
and natural selection, 147;
and movements of caterpillars, 146;
an inadequate basis for a theory of animal movements, 147.
Tunicates, suppressed notochord of, 250.
Unavailable energy and entropy, 375;
tendency to increase of, 375.
Unicellular organisms, energy-transformations in, 177.
Unit-characters, 230.
Van’t Hoff’s law, 218.
Variability, 172, 186;
continuous, 188;
discontinuous, 188;
examples of, 187;
and the environment, 189;
independent of the environment, 239;
and growth, 188;
tendencies of, 235.
Variation, rate of (mathematical), 344;
in biology, 186;
atavistic, 195;
direction of, 233;
fluctuating, 189;
must be co-ordinated, 231;
mathematical probability of co-ordination of 233;
the material for selection, 229;
origin of, 230;
selected by the organism, 237;
cause of, a pseudo-problem, 242;
arise de novo, 244.
Variables (mathematical), 343.
Varieties, specific, 194.
Vegetable life, 265.
Vertebrates, 249;
adaptations securing mobility, 275;
ancestry of, 253;
morphology of, 249;
a dominant group, 259;
distribution of, 260.
Verworn, and mechanism in life, 127.
Vesalius, anatomical school of, 121.
Vital activities, integration of, 128;
co-ordination of, 171.
de Vries and mutations, 191;
fluctuating variations inherited, 220.
Vital force, 318.
Van der Waal’s equation, 308.
Weber’s law, 16;
a quasi-mathematical relation, 17.
Weismann, hypothesis of heredity, 182;
hypothesis of germinal selection, 241;
hypothesis of development, 132;
mosaic-theory, 131;
preformation hypothesis, 133;
hypothesis of the germ-plasm, continuity of the germ-plasm, 181;
germinal changes inconceivable, 224;
size of biophors, 183;
origin of life, 339;
spontaneous generation a logical necessity, 339.
Weismannism, a series of logical hypotheses, 320;
physico-chemical analogies, and subsidiary hypotheses, 223.
Whales, an unsuccessful line of evolution, 274.
Whitehead, and mathematical reasoning, 347.
Wilson, mosaic-theory of development, 139.
Yerkes, and behaviour of crustacea, 293.
Zymogens, 92.
Zymoids, 94.
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Spelling corrections:
animo-acids → amino-acids
animo-substances → amino-substances
differen tkinds → different kinds
algae → algæ
organsim → organism (x2)
diffusbility → diffusibility
marjoity → majority
hythothesis → hypothesis
execretory → excretory
conconsidered → considered
*** End of this LibraryBlog Digital Book "The philosophy of biology" ***
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