Transcriber’s Note
In PROBLEM I, CHAPTER III, Section 45 (originally page 38), chemical
formulas represent the numbers of atoms in a molecule with patterns
like this: C_{114}. Throughout this eBook, pairs of underscores enclose
italicized text, Small-caps text appears as ALL-CAPS, and pairs of
equals signs enclose boldface text.
Works by the same Author.
=PROBLEMS OF LIFE AND MIND. The Foundations of a Creed.= Two
Volumes. Octavo. Per volume, $3.00.
CONTENTS: The Method of Science and its Applications to
Metaphysics--The Rules of Philosophizing--Psychological
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of Certitude--From the Known to the Unknown--Matter and
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THE
PHYSICAL BASIS OF MIND.
With Illustrations.
_BEING THE SECOND SERIES_
OF
PROBLEMS OF LIFE AND MIND.
BY
GEORGE HENRY LEWES.
[Illustration: The Riverside Press.]
BOSTON AND NEW YORK:
HOUGHTON, MIFFLIN AND COMPANY.
The Riverside Press, Cambridge.
1891.
AUTHOR’S EDITION.
_From Advance Sheets._
_The Riverside Press, Cambridge, Mass., U. S. A._
Printed by H. O. Houghton & Company.
PREFACE.
The title indicates that this volume is restricted to the group of
material conditions which constitute the organism in relation to the
physical world--a group which furnishes the data for one half of the
psychologist’s quest; the other half being furnished by historical and
social conditions.
The Human Mind, so far as it is accessible to scientific inquiry, has
a twofold root, man being not only an animal organism but an unit in
the social organism; and hence the complete theory of its functions and
faculties must be sought in this twofold direction. This conception
(which has been declared “to amount to a revolution in Psychology”),
although slowly prepared by the growing conviction that Man could not
be isolated from Humanity, was first expounded in the opening volume of
these _Problems of Life and Mind_; at least, I am not aware that any
predecessor had seen _how_ the specially human faculties of Intellect
and Conscience were products of social factors co-operating with the
animal factors.
In considering the Physical Basis a large place must be assigned to
the mechanical and chemical relations which are involved in organic
functions; yet we have to recognize that this procedure of Analysis is
artificial and preparatory, that none of its results are final, none
represent the synthetic reality of _vital_ facts. Hence one leading
object of the following pages has been everywhere to substitute
the biological point of view for the metaphysical and mechanical
points of view which too often obstruct research--the one finding its
expression in spiritualist theories, the other in materialist theories;
both disregarding the plain principle that the first requisite in a
theory of biological phenomena must be to view them in the light of
biological conditions: in other words, to fix our gaze upon what passes
in the organism, and not on what may pass in the laboratory, where
the conditions are different. Analysis is a potent instrument, but
is too often relied on in forgetfulness of what constitutes its real
aid, and thus leads to a disregard of all those conditions which it
has artificially set aside. We see this in the tendency of anatomists
and physiologists to assign to _one_ element, in a complex cluster of
co-operants, the significance which properly belongs to that cluster:
as when the property of a tissue is placed exclusively in a single
element of that tissue, the function of an organ assigned to its chief
tissue, and a function of the organism to a single organ.
Another object has been to furnish the reader uninstructed in
physiology with such a general outline of the structure and functions
of the organism, and such details respecting the sentient mechanism,
as may awaken an interest in the study, and enable him to understand
the application of Physiology to Psychology. If he comes upon details
which can only interest specially educated students, or perhaps
only by them be really understood, he can pass over these details,
for their omission will not seriously affect the bearing of the
general principles. I have given the best I had to give; and must
leave each reader to find in it whatever may interest him. The uses
of books are first to stimulate inquiry by awakening an interest;
secondly, to clarify and classify the knowledge already gained from
direct contemplation of the phenomena. They are stimuli and aids to
observation and thought. They should never be allowed to see for us,
nor to think for us.
The volume contains four essays. The first, on the _Nature of Life_,
deals with the speciality of organic phenomena, as distinguished
from the inorganic. It sets forth the physiological principles which
Psychology must incessantly invoke. In the course of the exposition I
have incorporated several passages from four articles on Mr. Darwin’s
hypotheses, contributed to the _Fortnightly Review_ during the year
1868. I have also suggested a modification of the hypothesis of Natural
Selection, by extending to the _tissues and organs_ that principle of
competition which Mr. Darwin has so luminously applied to _organisms_.
Should this generalization of the “struggle for existence” be accepted,
it will answer many of the hitherto unanswerable objections.
The second essay is on the _Nervous Mechanism_, setting forth what is
known and what is inferred respecting the structure and properties of
that all-important system. If the sceptical and revolutionary attitude,
in presence of opinions currently held to be established truths,
surprises or pains the reader unprepared for such doubts, I can only
ask him to submit my statements to a similar scepticism, and confront
them with the ascertained evidence. After many years of laborious
investigation and meditation, the conclusion has slowly forced
itself upon me, that on this subject there is a “false persuasion of
knowledge” very fatal in its influence, because unhesitatingly adopted
as the ground of speculation both in Pathology and Psychology. This
persuasion is sustained because few are aware how much of what passes
for observation is in reality sheer hypothesis. I have had to point out
the great extent to which Imaginary Anatomy has been unsuspectingly
accepted; and hope to have done something towards raising a rational
misgiving in the student’s mind respecting “the superstition of the
nerve-cell”--a superstition which I freely confess to have shared in
for many years.
The third essay treats of _Animal Automatism_. Here the constant
insistance on the biological point of view, while it causes a rejection
of the mechanical theory, admits the fullest recognition of all the
mechanical relations involved in animal movements, and thus endeavors
to reconcile the contending schools. In this essay I have also
attempted a psychological solution of that much-debated question--the
relation between Body and Mind. This solution explains why physical
and mental phenomena must necessarily present to our apprehension
such profoundly diverse characters; and shows that Materialism, in
attempting to deduce the mental from the physical, puts into the
conclusion what the very terms have excluded from the premises;
whereas, on the hypothesis of a physical process being only the
objective aspect of a mental process, the attempt to interpret the one
by the other is as legitimate as the solution of a geometrical problem
by algebra.
In the final essay the _Reflex Theory_ is discussed; and here once
more the biological point of view rectifies the error of an analysis
which has led to the denial of Sensibility in reflex actions, because
that analysis has overlooked the necessary presence of the conditions
which determine Sensibility. In these chapters are reproduced several
passages from the _Physiology of Common Life_.
According to my original intention, this volume was to have included an
exposition of the part I conceive the brain to play in physiological
and psychological processes, but that must be postponed until it can be
accompanied by a survey of psychological processes which would render
the exposition more intelligible.
THE PRIORY, March, 1877.
CONTENTS.
PROBLEM I. THE NATURE OF LIFE.
CHAPTER I.
PAGE
THE PROBLEM STATED 3
(_The Position of Biology_) 4
(_Organisms_) 8
(_Vital Force_) 14
(_Vital Force controlling Physical and Chemical Forces_) 16
CHAPTER II.
DEFINITIONS OF LIFE 24
CHAPTER III.
ORGANISM, ORGANIZATION, AND ORGANIC SUBSTANCE 37
(_Organism and Medium_) 45
(_The Hypothesis of Germinal Matter_) 57
(_Organisms and Machines_) 67
CHAPTER IV.
THE PROPERTIES AND FUNCTIONS 70
(_Does the Function determine the Organ?_) 78
CHAPTER V.
EVOLUTION 89
(_Natural Selection and Organic Affinity_) 115
(_Recapitulation_) 152
PROBLEM II. THE NERVOUS MECHANISM.
CHAPTER I.
SURVEY OF THE SYSTEM, 157
(_The Early Forms of Nerve-Centres_), 168
(_The Peripheral System_), 171
(_Ganglia and Centres_), 172
CHAPTER II.
THE FUNCTIONAL RELATIONS OF THE NERVOUS SYSTEM, 176
CHAPTER III.
NEURILITY, 189
(_Origins of Nerve-Force_), 201
(_The Hypothesis of Specific Energies_), 207
CHAPTER IV.
SENSIBILITY, 211
CHAPTER V.
ACTION WITHOUT NERVE-CENTRES, 227
CHAPTER VI.
WHAT IS TAUGHT BY EMBRYOLOGY?, 237
CHAPTER VII.
THE ELEMENTARY STRUCTURE OF THE NERVOUS SYSTEM, 251
(_Difficulties of the Investigation_), 252
(_The Nerve-Cell_), 258
(_The Nerves_), 270
(_The Neuroglia_), 273
(_The Relations of the Organites_), 278
(_Recapitulation_), 299
CHAPTER VIII.
THE LAWS OF NERVOUS ACTIVITY 310
(_The Energy of Neurility_) 311
(_The Propagation of Excitation_) 314
(_Stimuli_) 321
(_Stimulation_) 324
(_The Law of Discharge_) 326
(_The Law of Arrest_) 333
(_The Hypothesis of Inhibitory Centres_) 336
(_Anatomical Interpretations of the Laws_) 339
PROBLEM III. ANIMAL AUTOMATISM.
CHAPTER I.
THE COURSE OF MODERN THOUGHT 345
CHAPTER II.
THE VITAL MECHANISM 363
CHAPTER III.
THE RELATION OF BODY AND MIND 376
CHAPTER IV.
CONSCIOUSNESS AND UNCONSCIOUSNESS 399
CHAPTER V.
VOLUNTARY AND INVOLUNTARY ACTIONS 415
CHAPTER VI.
THE PROBLEM STATED 431
CHAPTER VII.
IS FEELING AN AGENT? 440
PROBLEM IV. THE REFLEX THEORY.
CHAPTER I.
THE PROBLEM STATED 467
CHAPTER II.
DEDUCTIONS FROM GENERAL LAWS 490
CHAPTER III.
INDUCTIONS FROM PARTICULAR OBSERVATIONS 509
(_Cerebral Reflexes_) 511
(_Discrimination_) 520
(_Memory_) 522
(_Instinct_) 522
(_The Acquisition of Instinct_) 536
(_Acquisition_) 546
CHAPTER IV.
NEGATIVE INDUCTIONS 550
PROBLEM I.
THE NATURE OF LIFE.
“La Physiologie a pour but d’exposer les phénomènes de la vie
humaine et les conditions d’où ils dépendant. Pour y arriver
d’une manière sûre, il faut nécessairement avant tout déterminer
quels sont les phénomènes qu’on désigne sous le nom de vie en
général. C’est pourquoi la première chose à faire est d’étudier
les propriétés générales du corps qu’on appelle organiques ou
vivans.”--TIEDEMANN, _Traité de Physiologie de l’Homme_, I. 2.
“Some weak and inexperienced persons vainly seek by dialectics and
far-fetched arguments either to upset or establish things that are
only to be founded on anatomical demonstration and believed on the
evidence of the senses. He who truly desires to be informed of the
question in hand must be held bound either to look for himself, or
to take on trust the conclusions to which they who have looked have
come.”--HARVEY, _Second Dissertation to Riolan_.
THE NATURE OF LIFE.
CHAPTER I.
THE PROBLEM STATED.
1. Although for convenience we use the terms Life and Mind as
representing distinct orders of phenomena, the one objective and the
other subjective, and although for centuries they have designated
distinct entities, or forces having different substrata, we may now
consider it sufficiently acknowledged among scientific thinkers that
every problem of Mind is necessarily a problem of Life, referring to
one special group of vital activities. It is enough that Mind is never
manifested except in a living organism to make us seek in an analysis
of organic phenomena for the material conditions of every mental fact.
Mental phenomena when observed in others, although interpretable by our
consciousness of what is passing in ourselves, can only be objective
phenomena of the vital organism.
2. On this ground, if on this alone, an acquaintance with the
general principles of structure and function is indispensable to
the psychologist; although only of late years has this been fully
recognized, so that men profoundly ignorant of the organism have had
no hesitation in theorizing on its highest functions. In saying that
such knowledge is indispensable, I do not mean that in the absence
of such knowledge a man is debarred from understanding much of the
results reached by investigators, nor that he may not himself make
useful observations and classifications of psychological facts. It is
possible to read books on Natural History with intelligence and profit,
and even to make good observations, without a scientific groundwork of
biological instruction; and it is possible to arrive at empirical facts
of hygiene and medical treatment without any physiological instruction.
But in all three cases the absence of a scientific basis will render
the knowledge fragmentary and incomplete; and this ought to deter
every one from offering an opinion on debatable questions which pass
beyond the limit of subjective observations. The psychologist who has
not prepared himself by a study of the organism has no more right to
be heard on the genesis of the psychical states, or of the relations
between body and mind, than one of the laity has a right to be heard on
a question of medical treatment.
THE POSITION OF BIOLOGY.
3. Science is the systematic classification of Experience. It
postulates unity of Existence with great varieties in the Modes of
Existence; assuming that there is one Matter everywhere the same,
under great diversities in the complications of its elements. The
distinction of Modes is not less indispensable than the identification
of the elements. These Modes range themselves under three supreme
heads: Force, Life, Mind. Under the first, range the general properties
exhibited by _all_ substances; under the second, the general properties
exhibited by _organized_ substances; under the third, the general
properties exhibited by organized _animal_ substances. The first
class is subdivided into _Physics_, celestial and terrestrial, and
_Chemistry_. Physics treats of substances which move as masses,
or which vibrate and rotate as molecules, without undergoing any
appreciable change of structural integrity; they show changes of
_position_ and _state_, without corresponding changes in their
elements. Chemistry treats of substances which undergo molecular
changes of composition _destructive_ of their integrity. Thus the blow
which simply moves one body, or makes it vibrate, explodes another. The
friction which alters the temperature and electrical state of a bit of
glass, ignites a bit of phosphorus, and so destroys its integrity of
structure, converting phosphorus into phosphoric acid.
4. The second class, while exhibiting both physical and chemical
properties, is markedly distinguished by the addition of properties
called vital. Their peculiarity consists in this: they undergo
molecular changes of composition and decomposition which are
simultaneous, and _by this simultaneity preserve their integrity of
structure_. They change their state, and their elements, yet preserve
their unity, and even when differentiating continue specific. Unlike
all other bodies, the organized are born, grow, develop, and decay,
through a prescribed series of graduated evolutions, each stage being
the indispensable condition of its successor, no stage ever appearing
except in its serial order.
5. The third class, while exhibiting all the characteristics of the
two preceding classes, is specialized by the addition of a totally
new property, called Sensibility, which subjectively is Feeling. Here
organized substance has become animal substance, and Vegetality has
been developed into Animality by the addition of new factors,--new
complexities of the elementary forces. Many, if not most, philosophers
postulate an entirely new Existence, and not simply a new Mode, to
account for the manifestations of Mind; they refuse to acknowledge
it to be a vital manifestation, they demand that to Life be added a
separate substratum, the Soul. This is not a point to be discussed
here. We may be content with the assertion that however great the
phenomenal difference between Humanity and Animality (a difference we
shall hereafter see to be the expression of a new factor, namely, the
social factor), nevertheless the distinctive attribute of Sensibility,
out of which rise Emotion and Cognition, marks the inseparable
_kinship_ of mental with vital phenomena.
Thus all the various Modes of Existence may, at least in their
objective aspect, be ranged under the two divisions of Inorganic and
Organic,--Non-living and Living,--and these are respectively the
objects of the cosmological and the biological sciences.
6. The various sciences in their serial development develop the
whole art of Method. Mathematics develops abstraction, deduction,
and definition; Astronomy abstraction, deduction, and observation;
Physics adds experiment; Chemistry adds nomenclature; Biology adds
classification, and for the first time brings into prominence the
important notion of _conditions of existence_, and the variation
of phenomena under varying conditions: so that the relation of the
organism to its medium is one never to be left out of sight. In
Biology also clearly emerges for the first time what I regard as the
true notion of causality, namely, the _procession_ of causes,--the
combination of factors in the product, and not an _ab extra_
determination of the product. In Vitality and Sensibility we are made
aware that the causes are _in_ and not _outside_ the organism; that
the organic effect is the organic cause in operation; that there is
autonomy but no autocracy; the effect issues as a resultant of the
co-operating conditions. In Sociology, finally, we see brought into
prominence the _historical conditions of existence_. From the due
appreciation of the conditions of existence, material and historical,
we seize the true significance of the principle of Relativity.
7. Having thus indicated the series of the abstract sciences we have
now to consider more closely the character of Biology. The term was
proposed independently yet simultaneously in Germany and France, in
the year 1802, by Treviranus and Lamarck, to express “the study of the
forms and phenomena of Life, the conditions and laws by which these
exist, and the causes which produce them.” Yet only of late years has
it gained general acceptance in France and England. The term Cosmology,
for what are usually called the Physical Sciences, has not yet come
into general use, although its appropriateness must eventually secure
its recognition.
Biology,--the abstract science of Life,--embracing the whole organic
world, includes Vegetality, Animality, and Humanity; the biological
sciences are Phytology, Zoölogy, and Anthropology. Each of the
sciences has its cardinal divisions, statical and dynamical, namely,
Morphology--the science of form,--and Physiology--the science of
function.
Morphology embraces--1°, _Anatomy_, i. e. the description of the parts
then and there present in the organism; and these parts, or organs, are
further described by the enumeration of their constituent tissues and
elements; and of these again the proximate principles, so far as they
can be isolated without chemical decomposition. 2°, _Organogeny_, i. e.
the history of the evolution of organs and tissues.
Physiology embraces the properties and functions of the tissues and
organs--the primary conditions of Growth and Development out of
which rise the higher functions bringing the organism into active
relation with the surrounding medium. The first group of properties
and functions are called those of vegetal, or organic life; the second
those of animal, or relative life.
ORGANISMS.
8. It will be needful to fix with precision the terms, Organism, Life,
Property, and Function.
An organism, although usually signifying a more or less complex unity
of organs, because the structures which first attracted scientific
attention were all thus markedly distinguished from inorganic
bodies, has by the gradual extensions of research been necessarily
generalized, till it now stands for any organized substance capable of
independent vitality: in other words, any substance having the specific
combination of elements which manifests the serial phenomena of growth,
development, and decay. There are organisms that have no differentiated
organs. Thus a microscopic formless lump of semifluid jelly-like
substance (Protoplasm) is called an organism, because it feeds itself,
and reproduces itself. There are advantages and disadvantages in such
extensions of terms. These are notable in the parallel extension of
the term Life, which originally expressing only the complex activities
of complex organisms, has come to express the simplest activities of
protoplasm. Thus a Monad is an organism; a Cell is an organism; a Plant
is an organism; a Man is an organism. And each of these organisms is
said to have its Life, because
“Through all the mighty commonwealth of things
Up from the creeping worm to sovereign man”[1]
there is one fundamental group of conditions, one organized substance,
one vitality.
Obviously this unity is an abstraction. In reality, the life manifested
in the Man is _not_ the life manifested in the Monad: he has Functions
and Faculties which the Monad has no trace of; and if the two organisms
have certain vital characteristics in common, this unity is only
recognized in an _ideal construction_ which lets drop all concrete
differences. The Life is different when the organism is different.
Hence any definition of Life would be manifestly insufficient which
while it expressed the activities of the Monad left unexpressed the
conspicuous and important activities of higher organisms. A sundial
and a repeater will each record the successive positions of the sun
in the heavens; but although both are instruments for marking time,
the sundial will not do the work of the repeater; the complexity and
delicacy of the watch mechanism are necessary for its more varied and
delicate uses. A semifluid bit of protoplasm will feed itself; but it
will not feed and sustain a complex animal; nor will it feel and think.
9. Neglect of this point has caused frequent confusion in the attempts
to give satisfactory definitions. Biologists ought to have been warned
by the fact that some of the most widely accepted definitions exclude
the most conspicuous phenomena of Life, and are only applicable to the
vegetable world, or to the vegetal processes in the animal world. A
definition, however abstract, should not exclude essential characters.
The general consent of mankind has made Life synonymous with Mode of
Existence. By the life of an animal is meant the existence of that
animal; when dead the _animal_ no longer exists; the substances of
which the organism was composed exist, but under another mode; their
connexus is altered, and the organism vanishes in the alteration.
It is a serious mistake to call the corpse an organism; for that
_special_ combination which constituted the organism is not present in
the corpse. This misconception misleads some speculative minds into
assigning life to the universe. The universe assuredly exists, but it
does not live; its existence can only be identified with life, such as
we observe in organisms, by a complete obliteration of the speciality
which the term Life is meant to designate. Yet many have not only
pleased themselves with such a conception, but have conceived the
universe to be an organism fashioned, directed, and sustained by a soul
like that of man--the _anima mundi_. This is to violate all scientific
canons. The life of a plant-organism is not the same as the life of an
animal-organism; the life of an animal-organism is not the same as the
life of a human-organism; nor can the life of a human-organism be the
same as the life of the world-organism. The unity of Existences does
not obliterate the variety of Modes; yet it is the speciality of each
Mode which Science investigates; to some of these Modes the term Life
is consistently applied, to others not; and if we merge them all in a
common term, we must then invent a new term to designate the Modes now
included under Life.
10. In resisting this unwarrantable extension of the term I am not
only pointing to a speculative error, but also to a serious biological
error common in both spiritualist and materialist schools, namely
that of assigning Life to other than organic agencies. Instead of
recognizing the speciality of this Mode of Existence as dependent on
a speciality of the organic conditions, the spiritualist assigns Life
to some extra-organic Vital Principle, the materialist assigns it to
some inorganic agent--physical or chemical. Waiving for the present all
discussion of Vitalism, let us consider in what sense we must separate
organic from all inorganic phenomena.
11. There is a distinction between inorganic and organic which may
fitly be called radical: it lies at the root of the phenomena, and must
be accepted as an ultimate fact, although the synthesis on which it
depends is analytically reducible to a complication of more primitive
conditions. It has been already indicated in § 5. All organisms above
the very simplest are syntheses Of three terms: Structure, Aliment,
and Instrument. Crystals, like all other anorganisms have structure,
and in a certain sense they may be said to grow (_Mineralia crescunt_),
though the growth is by _increase_ and not by _modification_:[2]
the motherlye, which is the food of the crystal, is never brought
to the crystal, nor prepared for it, by any instrumental agency of
the crystal. Organisms are exclusively instrumental; the organ is an
instrument. The structural integrity of an organism is thus preserved
through an alimentation which is effected through special instruments.
Nothing like this is visible in anorganisms.
The increase of a crystal is further distinguishable from the growth
of an organism, in the fact Of its being simple accretion without
development; and the structure of the crystal is distinguishable from
that of an organism in the fact that its integrity is preserved by
the _exclusion_ of all molecular change, and not by the simultaneous
changes of molecular decomposition and recomposition. Inorganic
substances are sometimes as unstable as organic, sometimes even more
unstable; but their instability is the source of their structural
destruction--they change into other species; whereas the instability
of _organized_ substances (_not_ of organic) is the source of their
structural integrity: the tissue is renovated, and its renovation is a
consequence of its waste.
12. But while the distinction is thus radical, when we view the
organism from the _real_--that is, from the synthetic point of view--we
must also urge the validity of the analytical point of view, which
seizes on the conditions here complicated in a special group, and
declares these conditions to be severally recognizable equally in
anorganisms and in organisms. All the fundamental properties of Matter
are recognizable in organized Matter. The elementary substances and
forces familiar to physicists and chemists are the materials of the
biologist; nor has there been found a single organic substance, however
special, that is not reducible to inorganic elements. We see, then,
that organized Matter is only a special combination of that which in
_other_ combinations presents chemical and physical phenomena; and we
are prepared to find Chemistry and Physics indispensable aids in our
analysis of organic phenomena. Aids, but only aids; indispensable, but
insufficient.
13. There is therefore an ambiguity in the common statement that
organized matter is not _ordinary_ matter. Indisputable in one sense,
this is eminently disputable when it is interpreted as evidence of
a peculiar Vital Force “wholly unallied with the primary energy of
Motion.” If by “ordinary matter” be meant earths, crystals, gases,
vapors, then assuredly organized matter is not ordinary. “Between the
_living_ state of matter and its _non-living_ state,” says Dr. Beale,
“there is an absolute and irreconcilable difference; so far from our
being able to demonstrate that the non-living passes by gradations
into or gradually assumes the scale or condition of the _living_, the
transition is sudden and abrupt, and matter already in the living
state may pass into the non-living condition in the same sudden and
complete manner.”[3] The ambiguity here is sensible in the parallel
case of the difference between crystallizable and coagulable matter, or
between one crystal and another. If we can decompose the organic into
the inorganic, this shows that the elements of the one are elements
of the other; and if we are not yet able to recompose the inorganic
elements into organic matter (not at least in its more complex forms),
may this not be due to the fact that we are ignorant of the proximate
synthesis, ignorant of the precise way in which the elements are
combined? I may have every individual part of a machine before me, but
unless I know the proper position of each, I cannot with the parts
reconstruct the machine. Indeed the very common argument on which so
much stress is laid in favor of some mysterious Principle as the source
of organic phenomena, namely, that human skill is hopelessly baffled in
the attempt to make organic substances, still more a living cell, is
futile. Men can make machines, it is said, but not organisms, _ergo_
organisms must have a spiritual origin. But the fact is that no man can
make a machine, _unless_ he take advantage of the immense traditions of
our race, and apply the skill of millions who have worked and thought
before him, slowly and tentatively discovering the necessary means
of mechanical effect. The greatest thinker, or the deepest scholar,
who did not place himself in the line of the tradition, and learn the
principles of mechanism, and the properties of the materials, would be
as incapable of making a watch, as the physiologist now is of making
a cell. But the skill of man has already succeeded in making many
organic substances, and will perhaps eventually succeed in making a
cell, certainly will, if ever the special synthesis which binds the
elements together should be discovered. Not that such a discovery would
alter the position of Biology in relation to Chemistry. The making of
albumen, nay, the construction of an organism in the laboratory, would
not in the least affect the foundation of Biology, would not obliterate
the radical difference between organisms and anorganisms. It is the
speciality of organic phenomena which gives them a special place,
although the speciality may only be due to a complication of general
agencies.
VITAL FORCE.
14. A similar ambiguity to that of the phrase “ordinary matter” lies
in the equally common phrase “Vital Force,” which is used to designate
a special group of agencies, and is then made to designate an agent
which has no kinship with the general group; that is to say, instead of
being employed in its real signification--that which alone represents
our knowledge--as the abstract statical expression of the complex
conditions necessary to the manifestation of vital phenomena, or as
the abstract dynamical expression of the phenomena themselves, it
is employed as an expression of their unknown Cause, which, because
unknown, is dissociated from the known conditions, and erected into
a mysterious Principle, having no kinship with Matter. In the first
sense the term is a shorthand symbol of what is known and inferred.
The known conditions are the relations of an organism and its medium,
the organism being the union of various substances all of which have
their peculiar properties when isolated; properties that disappear
in the union, and are replaced by others, which result from the
combination--as the properties of chlorine and sodium all disappear in
the sea-salt which results from their union; or as the properties of
oxygen and the properties of hydrogen disappear and are replaced by the
properties of water. When therefore Vital Force is said to be exalted
or depressed, the phrase has rational interpretation in the alteration
which has taken place in one or more of the conditions, internal and
external: a change in the tissues, the plasma, or the environment,
exalts or depresses the energy of the vital manifestations; and to
suppose that this is effected through the agency of some extra-organic
Principle is a purely gratuitous fiction.
15. That we are ignorant of one or more of the indispensable conditions
symbolized in the abstract term Vitality or Vital Force, is no reason
for quitting the secure though difficult path of Observation, and
rushing into the facile but delusive path of Fiction, which proposes
metempirical Agents (in the shape of Vital and Psychical Principles)
to solve the problems of Life and Mind. We may employ the term Vital
Force to label our observations, together with all that still remains
unobserved; and we are bound to recognize the line which separates
observation from inference, what is proved from what is inferred;
but while marking the limits of the known, we are not to displace
the known in favor of the unknown. It is said that because of our
ignorance we must assume these causes of Life and Mind to be _unallied_
with known material causes, and belonging to a different order of
existences. This is to convert ignorance into a proof; and not only
so, but to allow what we do not know to displace what we do know. The
organicist is ready to admit that much has still to be discovered; the
vitalist, taking his stand upon this unknown, denies that what has been
discovered is really important, and declares that the real agent is
wholly unallied to it. How _can_ he know this?
He does not know it; he assumes it; and the chief evidence he adduces
is that the ordinary laws of inorganic matter are incapable of
explaining the phenomena of organized matter; and that physical and
chemical forces are controlled by vital force. I accept both these
positions, stripping them, however, of their ambiguities. The laws of
ordinary matter are clearly incompetent in the case of matter which is
not ordinary, but _specialized_ in organisms; and when we come to treat
of Materialism we shall see how unscientific have been the hypotheses
which disregard the distinction. The question of control is too
interesting and important to be passed over here.
VITAL FORCE CONTROLLING PHYSICAL AND CHEMICAL FORCES.
16. The facts relied on by the vitalists are facts which every
organicist will emphasize, though he will interpret them differently.
When, for example, it is said that “Life resists the effect of
mechanical friction,” and the proof adduced is the fact that the
friction which will thin and wear away a dead body is actually the
cause of the thickening of a living--the skin of a laborer’s hand
being thickened by his labor; the explanation is not that Life, an
extra-organic agent, “resists mechanical friction”--for the mechanical
effect is _not_ resisted (the skin is rubbed off the rower’s hand
sooner than the wood is rubbed off the oar)--but that Life, i. e.
organic activity repairs the waste of tissue.
17. Again, although many of the physical and chemical processes which
invariably take place under the influences to which the substances
are subjected out of the organism, will not take place at all, or
will take place in different degrees, when the substances are in the
organism, this is important as an argument against the notion of vital
_phenomena_ being deducible from physical and chemical _laws_, but is
valueless as evidence in favor of an extra-organic agent. Let us glance
at one or two striking examples.
18. No experimental inquirer can have failed to observe the often
contradictory results which seemingly unimportant variations in the
conditions bring about; no one can have failed to observe what are
called chemical affinities wholly frustrated by vital conditions. Even
the ordinary laws of Diffusion are not always followed in the organism.
The Amœba, though semifluid, resists diffusion when alive; but when it
dies it swells and bursts by osmosis. The exchange of gases does not
take place in the tissues, precisely as in our retorts. The _living_
muscle respires, that is, takes up oxygen and gives out carbonic
acid, not on the principle of simple diffusion, but by two separable
physiological processes. The carbonic acid is given out, even when
there is no oxygen whatever present in the atmosphere, and its place
may then be supplied by hydrogen; and this physiological process is so
different from the physical process which goes on in the dead muscle
(the result of putrefaction), that it has been proved by Ranke to go
on when the temperature is so low that all putrefaction is arrested.
The same experimenter finds[4] that whereas living nerve will take up,
by imbibition, 10 per cent of potash salts, it will not take up 1 per
cent of soda salts, presented in equal concentration; and he points
to the general fact that the absorption of inorganic substances does
_not_ take place according to the simple laws of diffusion, but that
living tissues have special laws, the nerve, for instance, having
a greater affinity for neutral potash salts than for neutral soda
salts. Let me add, by way of anticipating the probable argument that
may urge this in favor of Vital Principle which is lightly credited
with the prescience of final causes, that so far from this “elective
affinity” of the tissues being intelligent and always favorable,
Ranke’s experiments unequivocally show that it is more active towards
destructive, poisonous substances, than towards the reparative,
alimentary substances; which is indeed consistent with the familiar
experience that poisons are more readily absorbed than foods, when both
are brought to the tissues. Thus it is well known that of all the salts
the sulphate of copper is that which plants most readily absorb--and
it kills them. The special affinities disappear as the vitality
disappears, and dying plants absorb all salts equally.
19. The more the organism is studied, the more evident it will become
that the simple laws of diffusion, as presented in anorganisms rarely
if ever take effect in tissues; in other words, what is called
Imbibition in Physics is the somewhat different process of Absorption
in Physiology.[5] The difference is notable in this capital fact, that
whereas the physical diffusion of liquids and gases is determined
by differences of density, the physiological absorption of liquids
and gases is determined by the molecular organization of the tissue,
which is perfectly indifferent to, and resists the entrance of, all
substances incapable of entering into organic combination, either as
aliment or poison. A curious example of the indifference of organized
substances to some external influences and their reaction upon others,
is the impossibility of provoking ciliary movement in an epithelial
cell, during repose, by any electrical, mechanical, or chemical stimuli
except potash and soda. Virchow discovered that a minute quantity of
either of these, added to the water in which the cell floated, at once
called forth the ciliary movements.
20. The true meaning of the resistance of Vitality to ordinary chemical
affinity is, that the conditions involved in the phenomena of Vitality
are not the conditions involved in the phenomena of Chemistry; in other
words, that in the living organism the substances are placed under
conditions different from those in which we observe these substances
when their chemical affinities are displayed in anorganisms. But we
need not go beyond the laboratory to see abundant examples of this
so-called resistance to chemical affinity, when the conditions are
altered. The decomposition of carbonates by tartaric acid is a chemical
process which is wholly resisted if alcohol instead of water be the
solvent employed. The union of sulphur with lead is said to be due
to the affinity of the one for the other; but no one supposes this
affinity to be irrespective of conditions, or that the union will take
place when any one of these conditions is absent. If we fuse a compound
of lead and iron in a crucible containing sulphur, we find it is the
iron, and not the lead, which unites with the sulphur; yet we do not
conclude that there is a Crucible Principle which frustrates chemical
affinity and resists the union of sulphur and lead; we simply conclude
that the presence of the iron is a condition which prevents the
combination of the sulphur with the lead: not until all the iron has
taken up its definite proportion of sulphur will the affinity of the
lead come into play. This is but another illustration of the law that
_effects are processions of their causes_, summations of the conditions
of their existence. If the fire burns no hole in the teakettle so long
as there is water to conduct the heat away, this is not due to any
principle more mysterious than the presence of a readily conducting
water.[6]
21. In accordance with the law of Causation just mentioned, which
has been expounded in detail in our First Series (Vol. II. p. 335),
the special combinations of Matter in organisms must present special
phenomena. Therefore since the province of Biology is that of
explaining organic phenomena by means of their organic conditions,
it must be radically distinguished from the provinces of Physics and
Chemistry, which treat not of organized but of inorganic matter. It
is idle, it is worse, for it is misleading, to personify the organic
conditions, known and inferred, in a Vital Principle; idle, because we
might with equal propriety personify the conditions of crystallization
in a Crystal Principle; misleading, because the artifice is quickly
dropped out of sight, and the abstract term then becomes accepted as
an entity, supposed to create or rule the phenomena it was invented to
express.
22. Inquirers are but too apt to misconceive the value of Analysis,
which is an artifice of Method indispensable to research, though
needing the complementary rectification by Synthesis before a real
explanation can be reached. Analysis decomposes the actual fact into
ideal factors, separates the group into its components, and considers
each of these, not as it exists in the group, in the reality, but as
it exists when theoretically detached from the others. The oxygen
and hydrogen into which water is decomposed did not exist as these
gases in the water; the albumen and phosphate we extract from a nerve
did not exist _as_ isolated albumen and phosphate in the nerve, they
were molecularly combined. In like manner the physical and chemical
processes which may analytically be inferred in vital processes do
not really take place in the same way as out of the organism. The
real process is always a vital process, and must be explained by the
synthesis of all the co-operant conditions. The laws of Physics and
Chemistry formulate abstract expressions of phenomena, wherever and
whenever these appear, without reference to the _modes of production_;
and in _this_ sense the movement of a limb is no less a case of
Dynamics than the movement of a pulley--the decomposition of a tissue
is a case of Chemistry no less than the decomposition of a carbonate;
the electromotor phenomena observed in muscle are as purely physical
as those observed in a telegraph. But when a biologist has to explain
the movements of the limbs, or the decompositions of tissues, he has
to deal with the phenomena and their modes of production, he has
a particular group before him, and must leave out nothing that is
characteristic of it. The movements of the pulley do not depend on
Contractility and Sensibility, which in turn depend on Nutrition. The
decomposition of the carbonate does not depend on conditions resembling
those of a living tissue. Vaucanson’s duck was surprisingly like a
living duck in many of its movements; but in none of its actions was
there any real similarity to the actions of a bird, because the machine
was unlike an organism in action. The antithesis of mechanism and
organism will be treated of in § 78.
23. We conclude, then, that defining physical phenomena as the
movements which take place _without_ change of structure, and chemical
phenomena as the movements _with_ change of structure, although
both classes may be said to take place in the organism, and to be
the primary conditions on which organic phenomena depend, they do
not embrace the whole of the conditions, nor are the sciences which
formulate them capable of formulating either the special phenomena
characteristic of organisms or their special modes of production. The
biologist will employ chemical and physical analysis as an essential
part of his method; but he will always rectify what is artificial in
this procedure, by subordinating the laws of Physics and Chemistry
to the laws of Biology revealed in the synthetic observation of
the organism as a whole. The rectification, here insisted on, will
be recognized as peculiarly urgent in Psychology, which has greatly
suffered from the misdirection of Analysis.
24. No one will misunderstand this specialization of Biology to mean
a separation of Life from the series of objective phenomena, and
the introduction of a new entity; the specialization points to a
Mode of Existence. All classifications are artifices, but they have
their objective grounds; the ground of difference on which Biology
is separated from Chemistry and Physics, though all three may be
merged in a common identity, is such as to justify the term radical.
A vital process is no more to be considered physico-chemical, because
physico-chemical conditions are presupposed in it, than a feeling is
to be considered a nutritive process, because Nutrition is presupposed
in all Feeling. Organic substances have been made by chemists, and
inorganic “cells” have also been made; but these substances were not
organized, these “cells” would not live. The germ-cell is the workshop
of generation, the secreting-cell the workshop of secretion, the
muscle-cell the workshop of contraction. What is required over and
above organic substances and cell-forms, is that special state called
_organization_. See § 49.
Those who contemplate the manifestations without also taking into
account their modes of production may see nothing but physico-chemical
facts in vital facts. It is by a similar limitation of the point of
view that Vitality is often confounded with Movement, and portions
of organic matter are said to live, simply on the evidence of their
movements.[7]
CHAPTER II.
DEFINITIONS OF LIFE.
25. Biology, the science of Life, being thus assigned its place in the
hierarchy of objective laws, we now proceed to consider what the term
Life symbolizes.
By a large preliminary simplification, Life may be defined as _the
mode of existence of an organism in relation to its medium_. To render
this of any value, however, a clear conception of the organism is
first indispensable; and this must be preceded by an examination of
the various attempts to define life in anticipation of such a clear
conception.
26. Every phenomenon, or group of phenomena, may be viewed under
two aspects--the _statical_, which considers the conditions of
existence; and the _dynamical_, which considers these conditions in
their resultant,--in their _action_. The statical definition of Life
will express the connexus of the properties of organized substance,
all those conditions, of matter, form, and texture, and of relation
to external forces, on which the organism depends. These various
conditions, condensed into a single symbol, constitute Vitality or
Vital Force, and are hence taken as the Cause of vital phenomena.
The dynamical definition will express the connexus of Functions and
Faculties of the organism, which are the statical properties of
organized substance in action, under definite relations.
It is obvious that the term Life must vary with the varying
significates it condenses,--every variation in the complexity of the
organism will bring a corresponding fulness in the signification of
the term. The life of a plant is less significant than the life of
an animal; and the life of a mollusc less than that of a fish. But
not only is the term one of varying significance, it is always an
abstract term which drops out of sight particular concrete differences,
registering only the universal resemblances.
* * * * *
27. It would be a profitless labor to search out, and a wearisome
infliction to set down, the various definitions which have been
proposed and accepted; but certain characteristic examples may be
selected. All that I am acquainted with belong to two classes: 1°, the
_meta_-physiological hypothesis of an _extra_-organic agent, animating
lifeless matter by unknown powers; 2°, the physiological hypothesis
which seeks the cause of the phenomena (i. e. the conditions) _within_
the organism itself,--a group of conditions akin to those manifested
elsewhere, but differently combined. The first hypotheses are known
under the names of Animism and Vitalism,--more commonly the latter. The
second are known as Organicism and Materialism,--but the latter term
only applies to some of the definitions.
28. Under Vitalism are included all the hypotheses of a soul, a spirit,
an archæus, a vital principle, a vital force, a _nisus formativus_,
a plan or divine idea, which have from time to time represented the
metaphysical stage of Biology. The characteristic of that stage is
the personification of a mystery, accompanied by the persuasion that
to name a mystery is to explain it. In all sciences when processes
are imperfectly observed, the _theory_ of the processes (which is a
systematic survey of the available evidence marshalled in the order
of causal dependence) is supplemented by _hypothesis_, which fills up
with a guess the gap left by observation. The difference between the
metaphysical and the positive stages of a science lies in the kind of
guess thus introduced to supplement theory, and the degree of reliance
accorded to it. I have more than once insisted on the scientific
canon that “to be valid, an explanation must be expressed in terms of
phenomena already observed”; now it is quite clear that most of the
extra-organic hypotheses do not fulfil this condition; no one having
ever _observed_ a spirit, an archæus, or a vital principle; but only
_imagined_ these agents to explain the facts observed. As an example of
the difference, and a proof that the value of an hypothesis does not
rest on the facility with which it connects observations, and seems
to explain them, take the three hypotheses of animal spirits, nervous
fluid, and electricity, by which neural processes have been explained.
The animal spirits are imaginary; the nervous fluid is without a basis
in observation, no evidence of such a fluid having been detected;
but electricity (or, speaking rigorously, the movements classed as
electrical), although not proved to be _the_ agent in nerve-action,
is proved to exist in nerves as elsewhere, and its modes of operation
are verifiable. It, therefore, and it alone of the three hypotheses,
is in conformity with the scientific canon. It may not, on full
investigation, meet all requirements; it may be rejected as imperfect;
but it is the kind of guess which scientific theory demands.
The second difference noticeable between the metaphysical and the
positive stages is the degree of reliance accorded to hypothesis;
which is very much the same as that noticeable in the uncritical and
critical attitudes of untrained and trained intellects. The one accepts
a guess as if it were a proof; is fascinated by the facility of linking
together isolated observations, and, relying on the guess as truth,
proceeds to deduce conclusions from it; the other accepts a guess as
an aid in research, trying by its aid to come upon some observation
which will reveal the hidden process; but careful never to allow the
guess to _supersede observation_, or to form a basis of deductions not
immediately verified.
29. A glance at the metaphysiological definitions will detect both the
kind of guess and the kind of reliance which prevailed. The mystery
was not simply recognized, it was personified as an entity: Will and
Intelligence were liberally accorded to it, for it was supposed to
shape matter, and direct force into predestined paths by prescience of
a distant end. The observed facts of the egg passing through successive
changes into a complex organism were so marvellous, so unlike any
facts observable in the inorganic world, that they seemed to demand a
cause drawn from higher sources. The mystery of life obtruded itself
at every turn. It was named, and men fancied it explained. But in
truth no mystery is got rid of by explanation, however valid; it is
only shifted farther back. Explanation is the resolution of a complex
phenomenon into its conditions of existence--the product is reduced to
its factors; the explanation is final when this resolution has been
so complete that a reconstruction of the product is possible from
the factors. The vast majority of explanations--especially in the
organic region--are no more than what mathematicians call “a first
approximation.” It is through successive approximations that science
advances; but even when the final stage is reached a mystery remains.
We may know that certain elements combine in certain proportions
to produce certain substances; but why they produce these, and not
different substances, is no clearer than why muscles contract or
organisms die. This Why is, however, an idle question. That alone which
truly concerns us is the How, and not the Why.
30. Biology is still a long way off the How. But it can boast of
many approximations; and its theories are to be tested by the degree
of approximation they effect. In this light the physiological,
_intra_-organic, hypotheses manifestly have the advantage. Many of them
are indeed very unacceptable; they are guided by a mistaken conception
of the truths reached by Analysis. For when men first began to discard
the extra-organic hypotheses, and to look into the organism itself,
they were so much impressed by the mechanical facts observed, that they
endeavored to reduce all the phenomena to Mechanics. The circulation
became simply a question of hydraulics. Digestion was explained as
trituration. The chemists then appeared, and their shibboleths were
“affinities” and “oxidations.” With Bichat arose the anatomical school,
which decomposing the organism into organs, the organs into tissues,
and these tissues into their elements, sought the analytical conditions
of existence of the organism in the properties of these tissues, and
the functions of these organs. The extra-organic agent was thus finally
shown to be not only a fiction, but a needless fiction.
Every student of the history of the science will note how from the very
necessities of the case the metaphysiologists, without relinquishing
their Vital Principle, have been led more and more to enter on the
track of the physiologists, pursuing their researches more and more
into the processes going on in the organism, and assigning more and
more causal efficiency to these, with a corresponding restriction
of the province of their extra-organic cause. Hence in the ranks of
the vitalists have been found some of the very best observers and
theorists; but they were such in despite of, and not in consequence
of, their hypothesis, which was only invoked by them when evidence
was at fault. Nor, unscientific as vitalism is, can we deny that it
has been so far serviceable to the science, that it has corrected the
materialist error of endeavoring to explain organic phenomena by
physico-chemical laws; and has persistently kept in view the radical
difference between organic and inorganic.
31. These remarks may justify a selection of definitions, classified
under the two heads. The selection is fitly opened by the Aristotelian
definition which prevailed for centuries.
Aristotle distinguishes Life, which he says means “the faculties of
self-nourishment, self-development, and self-decay,” from the Vital
Principle. Every natural body manifesting life may be regarded as an
essential existence (οὐσία); but _then it is an existence only as a
synthesis_ (ὡς συθέτη); and since an organism is such a synthesis,
being possessed of Life, it cannot be the Vital Principle (ψυχή).
Therefore it follows that the Vital Principle must be an essence, as
being the Form of a natural body holding life in _potentiality_. The
Vital Principle is the primary reality of an organism. “It is therefore
as idle to ask whether the Vital Principle and Organism are one, as
whether the wax and the impress on it are one.... Thus if an eye
were an animal, Vision would be its Vital Principle: for Vision is,
abstractedly considered, the essence of the eye; but the eye is the
body of Vision, and if Vision be wanting, then, save in name, it is no
longer an eye.”
Apart from certain metaphysical implications, inevitable at that
period, there is profound insight in this passage. His adversary
Telesio quite misconceives the meaning here assigned to the Vital
Principle.[8]
32. Let us pass over all the intermediate forms of the hypothesis, and
descend to Kant, who defines Life “an internal principle of action”
(this does not distinguish it from fermentation); an organism he says
is “that in which every part is at once means and end.” “Each part
of the living body has its cause of existence in the whole organism;
whereas in non-living bodies each part has its cause in itself.”
Johannes Müller adopts a similar view: “The harmonious action of the
essential parts of the individual subsist only by the influence of a
force, the operation of which is extended to all parts of the body,
and does not depend on any single parts; this _force must exist before
the parts_, which are in fact formed by it during the development of
the embryo.... The vital force inherent in them generates from the
organic matter the essential organs which constitute the whole being.
This _rational creative force_ is exerted in every animal strictly in
accordance with what the nature of each requires.”
33. This is decidedly inferior to Aristotle, who did not confound
the vegetative with the rational principle. It rests on the old
metaphysical error of a _vis medicatrix_, an error which cannot
sustain itself against the striking facts which constantly point to
a _vis destructrix_, a destructive tendency quite as inexorable as
the curative tendency. And the experimental biologist soon becomes
impressed with the fact that the tissues have indeed a _selective_
action, by which from out the nutrient material only these substances
are assimilated which will enter into combination with them; but this
selective action is fatal, no less than reparative: substances which
poison the tissue are taken up as readily as those which nourish
it. The idea of prescience, therefore, cannot be sustained; it is
indeed seldom met with now in the writings of any but the Montpellier
school, who continue the traditions of Stahl’s teaching. It has been
so long exploded elsewhere that one is surprised to find an English
physiologist clinging to a modification of it--I mean Dr. Lionel Beale,
who repeatedly insists on Life as “a peculiar Force, _temporarily
associated_ with matter,” a “power capable of controlling and directing
both matter and force,” an “_undiscovered_ form of force _having no
connection with primary energy or motion_.” “The higher phenomena of
the nervous system are probably due primarily to the movements of the
germinal matter due to vital power, which vital power of this the
highest form of germinal matter is in fact the living _I_.”
34. Apart from the primary objection to all these definitions,
namely, that they seek to express organic phenomena in terms of an
extra-organic principle, to formulate the facts _observed_ in terms
of a cause _inferred_, there is the fatal objection that they speak
confidently on what is avowedly unknown. If the force be, as Dr. Beale
says, “undiscovered,” on what grounds can he assert that it has _no_
connection with the forces which are known? All that the observed facts
warrant is the assertion that organic phenomena are special (which
no one denies), and must therefore depend on special combinations of
matter and force. But on this ground we might assume a crystallizing
Force, and a coagulating Force, having no connection with the molecular
forces manifested elsewhere: these also are special phenomena, not to
be confounded with each other.
35. Schelling defines Life as “a principle of individuation” and a
“cycle of successive changes determined and fixed by this internal
principle.” Which is so vague that it may be applied in very different
senses. Bichat’s celebrated definition (which is only a paraphrase of
a sentence in Stahl), “the sum of the functions which resist Death,”
although an endeavor to express the facts from the Intra-organic point
of view, is not only vague, but misrepresents one of the cardinal
conditions, by treating the External Medium as antagonistic to Life,
whereas Life is only possible in the relation to a Medium.
36. Were it not so vague, the definition proposed by Dugès and Béclard
would be unexceptionable: the former says it is “the special activity
of organized beings”; the latter, “the sum of the phenomena proper to
organized bodies.” When supplemented by a description of organized
bodies, these formulæ are compendious and exact. The same remark
applies to the definition of Lamarck: “that state of things which
permits organic movements; and these movements, which constitute active
life, result from a stimulus which excites them.”
37. De Blainville, and after him Comte and Charles Robin, define
it thus: “Life is the twofold internal movement of composition and
decomposition at once general and continuous.” This, excellent as
regards what is called vegetal life, is very properly objected to by
Mr. Herbert Spencer in that it excludes those nervous and muscular
functions which are the most conspicuous and distinctive of vital
phenomena. The same objection must be urged against Professor Owen’s
definition: “Life is a centre of intussusceptive assimilative force
capable of reproduction by spontaneous fission.”
38. In 1853, after reviewing the various attempts to express in a
sentence what a volume could only approximately expound, I proposed the
following: “Life is a series of definite and successive changes, both
of structure and composition, which take place within an individual
without destroying its identity.” This has been criticised by Mr.
Herbert Spencer and by Dr. Lionel Beale, and if I had not withdrawn
it before their criticisms appeared, I should certainly have modified
and enlarged it afterwards. I mention it, however, because it is an
approach to a more satisfactory formula in so far as it specifies two
cardinal characteristics distinguishing organisms from all anorganisms,
namely, the incessant evolution through definite stages, and the
preservation of specific integrity throughout the changes; not only
the organism as a whole is preserved amidst incessant molecular
change, but each tissue lives only so long as the reciprocal molecular
composition and decomposition persist. On both of these points I shall
have to speak hereafter. The definition, however, is not only defective
in its restriction to the molecular changes of Nutrition, taking no
account of the Properties and Functions of the organism; but defective
also in giving no expression to equally important relations of the
organism to the medium.
39. This last point is distinctly expressed in Mr. Spencer’s
definition: “Life is the continuous adjustment of internal relations
to external relations.” Considered as a formula of the most general
significance, embracing therefore what is common to all orders of vital
phenomena, this is the best yet proposed.[9] If I propose another it
will not be to displace but to run alongside with Mr. Spencer’s; and
this only for more ready convenience. Before doing so I must say a few
words by way of clearing the ground.
40. What does the term Life stand for? What are the concrete
significates of this abstract symbol? As before stated, it is sometimes
a compendious shorthand for the special phenomena distinguishing living
from non-living bodies; and sometimes it expresses not these observed
phenomena, but their conditions of existence, which are by one school
personified in an abstract and extra-organic cause. Thus the life of
an animal, a man, or a nation, means--1°, the special manifestations
of these organisms, and groups of organisms; or 2°, the causes which
produce these manifestations. We are often misunderstood by others, and
sometimes vague to ourselves, when we do not bear these two different
meanings in view. It was probably some sense of this which made
Aristotle distinguish Vitality from Life, as that of the one uniform
cause separated from its multiple effects; it was certainly the motive
of Fletcher, who thus expressly limits the meanings: “_Vitality_ or
_Irritability_, the property which characterizes organized beings
of being acted on by certain powers otherwise than either strictly
mechanically or strictly chemically; _Life_, the sum of the actions
of organized beings resulting directly from their vitality so acted
on.”[10]
Vitality and Life being thus discriminated as the statical and
the dynamical aspects of the organism, we find in relation to the
former two radically opposed conceptions: the metaphysiological or
extra-organic, and the physiological or intra-organic. The first
conceives Vitality to be a Vital Principle, or extra-organic agent,
sometimes a soul, spirit, archæus, idea, and sometimes a force, which
easily becomes translated into a property.
The conception of an entity must be rejected, because it is
metempirical and unverifiable, § 34. The conception of a force must
be rejected, because it is irreconcilable with any definite idea we
have of force. What the term Force signifies in Physics and Chemistry,
namely, mass animated by velocity, or _directed pressure_, which is
the activity of the agent,--is precisely that which these vitalists
pertinaciously exclude. They assume a force which has nothing in
common with mass and velocity; which is _not a resultant, but a
principle_; which instead of being a _directed quantity_, is itself
autonomous and _directive_, shaping matter into organization, and
endowing it with powers not assignable to matter. If this vital force
has any mass at its back, it is a spiritual mass; if it is directed,
the direction issues from a “Mind somewhere.” Now this conception is
purely metempirical. Not only is it inexact to speak of Vitality as
a force, it is almost equally inexact to speak of it as a property;
since it is a term which includes a variety of properties; and when
Fletcher assigns the synonym of Irritability, this at once reveals the
inexactness; for beside this property, we must place Assimilation,
Evolution, Disintegration, Reproduction, Contractility, and
Sensibility,--all characteristic properties included in Vitality.
41. Having thus rejected the conceptions of entity, force, and
property, we are left in presence of--1°, the organic conditions as the
elements, and 2°, of their synthesis (in the state called organization)
as the personified principle. Vital forces, or the vital force, if
we adopt the term for brevity’s sake, is a _symbol of the conditions
of existence of organized matter_; and since organisms are specially
distinguishable from anorganisms by this speciality of their synthesis,
and not by any difference in the nature of the elements combined, this
state of organization is the “force” or “principle” of which we are in
quest. To determine what Life means, we must observe and classify the
phenomena presented by living beings. To determine what Vitality--or
organization--means, we must observe and classify the processes which
go on in organized substances. These will occupy us in the succeeding
chapters; here I may so far anticipate as to propose the following
definitions:--
42. Life is the functional activity of an organism in relation to
its medium, as a synthesis of three terms: Structure, Aliment, and
Instrument; it is the sum of functions which are the resultants of
Vitality; Vitality being the sum of the properties of matter in the
state of organization.
43. Vital phenomena are the phenomena manifested _in_ organisms when
external agencies disturb their molecular equilibrium; and _by_
organisms when they react on external objects. Thus everything done in
an organism, or by an organism, is a vital act, although physical and
chemical agencies may form essential components of the act. If I shrink
when struck, or if I whip a horse, the blow is in each case physical,
but the shrinking and the striking are vital.
Every part of a living organism is therefore vital, as _pertaining_
to Life; but no part has this Life when isolated; for Life is the
synthesis of all the parts: a federation of the organs when the
organism is complex, a federation of the organic substances when the
organism is a simple cell.
44. All definitions, although didactically placed at the introduction
of a treatise, are properly the final expression of the facts which
the treatise has established, and they cannot therefore be fully
apprehended until the mind is familiarized with the details they
express. Much, therefore, which to the reader may seem unintelligible
or questionable in the foregoing definition, must be allowed to pass
until he has gone through the chapters which follow.
CHAPTER III.
ORGANISM, ORGANIZATION, AND ORGANIC SUBSTANCE.
45. There is a marked difference between organ_ic_ and organ_ised_
substances. The organic are non-living, though capable of living
when incorporated in organized tissue (albumen is such a substance);
or they may be incapable of living because they have lived, and are
products of waste, e. g. urea. The organized substance is a specific
combination of organic substances of various kinds, a combination
which is organization. Any organized substance is therefore either an
independent organism, or part of a more complex organism. Protoplasm,
either as a separate organism or as a constituent of a tissue, is
organized substance.
Organic substances are numerous and specific. They are various
combinations of proximate principles familiar to the chemist, which may
conveniently be ranged under three classes: The first class of organic
substances comprises those composed of principles having what is called
a mineral origin; these generally quit the organism unchanged as they
entered it. The second class comprises those which are crystallizable,
and are formed _in_ the organism, and generally quit it in this state
as excretions. The third class comprises the colloids, i. e. substances
which are coagulable and not crystallizable, and are formed in and
decomposed in the organism, thus furnishing the principles of the
second class. All the principles are in a state of solution. Water is
the chief vehicle of the materials which enter and the materials which
quit the organism; and bodies in solution are solvents of others, so
that the water thus acquires new solvent properties.
45_a_. Two points must be noted respecting organic substances: they are
mostly combinations of _higher multiples_ of the elements; and their
combinations are not _definite_ in quantity. Albumen, for example,
has (according to one of the many formulas which have been given) an
elementary composition of 216 atoms of Carbon, 169 of Hydrogen, 27 of
Nitrogen, 3 of Sulphur, and 68 of Oxygen; whereas in its final state,
in which it quits the organism as Urea, it is composed of 2 atoms
of Carbon, 4 of Hydrogen, 2 of Nitrogen, and 2 of Oxygen, all the
Sulphur having disappeared in other combinations. In like manner in
the organism Stearin falls from C_{114}, H_{110}, O_{12}, to Oxalic
Acid, which is C_{4}, H_{2}, O_{8}. It is obvious that the necessary
modifiability of organic substance is due to this multiplicity of its
elementary parts and the variety of its molecular structure.
45_b_. Nor is the indefiniteness of the quantitative composition less
important, though seldom adequately appreciated, or even suspected.
Robin and Verdeil[11] are the only writers I can remember who have
distinctly brought the fact into prominence. That all inorganic
substances are definite in composition, every one knows. Quicklime,
for example, may be got from marble, limestone, oyster-shells, or
chalk; but however produced, it always contains exactly 250 ounces
of calcium to 100 ounces of oxygen; just as water is always OH_{2}.
Not so the pre-eminently vital substances, those which are coagulable
and not crystallizable: no precise formula will express one of these;
for the same specific substance is found to vary from time to time,
and elementary analyses do not give uniform results. Thus, if after
causing an acid to combine with one of these substances, we remove
the acid, we are not certain of finding the substance as it was
before--as we are, for example, after urea is combined with nitric
acid and then decomposed. The same want of definiteness is of course
even more apparent in the _combinations_ of these proximate principles
into organized substance. Protoplasm differs greatly in different
places. Epithelial cells differ. Muscular and nervous fibres are never
absolutely the same in different regions. A striped and unstriped
muscular fibre, the muscular fibre of a sphincter or of a limb, a
nerve-fibre in a centre, in a trunk, or in a gland, will present
variations of composition. The elastic fibres of the ligaments are
larger in the horse than in man; and in other animals they are smaller.
These differences are sometimes due to the constituents, and sometimes
to the arrangement of the constituents; the conversion of Albumen into
Fibrine without elementary loss or addition, is a good example of the
latter. That the tissues of one man are not absolutely the same as
the tissues of another, in the sense in which it is true to say that
the chalk of one hill is the same as that of another, or as gold in
Australia is the same as gold in Mexico, is apparent in their very
different reactions under similar external conditions: the substance
which poisons the one leaves the other unaffected. The man who has once
had the small-pox, or scarlet fever, is never the same afterwards,
since his organism has now become insusceptible of these poisons. And
Sir James Paget has called attention to the striking fact revealed in
disease, namely, that in the same tissue--say the bone or the skin--a
morbid substance fastens only on certain small portions leaving all
the rest unaltered, but fastens on exactly corresponding spots of the
opposite sides of the body; so that on both arms, or both legs, only
the corresponding bits of tissue will be diseased. “Manifestly when
two substances display different relations to a third their composition
cannot be identical; so that though we may speak of all bone or
of all skin as if it were all alike, yet there are differences of
intimate composition. No power of artificial chemistry can detect the
difference; but a morbid material can.”[12] It is to this variability
of composition that we must refer individual peculiarities, and those
striking forms of variety known as idiosyncrasies, which cause some
organisms to be affected by what seem inexplicable influences--physical
and moral.
In spite of all these variations, however, there are certain specific
resemblances dependent of course on similarity of composition and
structure, so that the muscle of a crustacean is classed beside the
muscle of a vertebrate, although the elementary analysis of the two
yields different results. Nerve-tissue, according to my experience,
is the most variable of all, except the blood; variable not only from
individual to individual, and from genus to genus, but even in the same
individual it never contains the same quantities of water, phosphates,
etc. Hence it is that different nerves manifest different degrees of
excitability, and the same nerve differs at different times. Thus the
fifth pair, in a poisoned animal, retains its excitability long after
the others are paralyzed; and the patient under chloroform feels a
prick on the brow or at the temples, when insensible at any other spot.
The pneumogastric which is excitable during digestion is--in dogs at
least--inexcitable when the animal is fasting.
46. The organic substances are what analysis discovers in organized
substances, but none of them, not even the highest, is living, except
as organized. Albumen alone, or Stearin alone, is as incapable of
Vitality, as Plumbago, or Soda; but all organic substances are
capable of playing a part in vital actions; and this part is the
more important in proportion to their greater molecular variety.
Organization is a special synthesis of substances belonging to all
three classes; and the organized substance, thus formed, alone merits
the epithet living. We see how organized substances, being constituted
by principles derived from the inorganic world, and principles derived
from the organic world, have at once a dependence on the external
Medium, and an independence of it, which is peculiar to living beings.
An analogous dependence and independence is noticeable with respect to
the parts; and this is a character not found in inorganic compounds.
The organism, even in its simplest forms, is a structure of different
substances, each of which is complex. While one part of a crystal is
atomically and morphologically identical with every other, and is the
whole crystal “writ small,” one part of an organism is unlike another,
and _no part_ is like the whole. Hence the dependence of one organ and
one tissue on another, and each on all. Yet, while every part is, so to
speak, a condition of existence of every other, and the unity of the
organism is but the expression of this solidarity,--wherever organized
substance has been differentiated into morphological elements (cells,
etc.), each of these has its own course of evolution independently of
the others,--is born, nourished, developed, and dies.
47. The interdependence of nerve and muscle is seen in this, that the
more the muscle is excited the feebler its contractions become; this
decrease in contractility is compensated by an increased excitability
in its nerve; so that while the muscle demands a more powerful
stimulus, the nerve acquires a more energetic activity. Ranke’s curious
and careful experiments seem to prove that this depends on the wearied
muscle absorbing more water, owing to the acids developed by its
activity, and on the nerve losing this water--a nerve being always
more irritable when its quantity of water diminishes.
48. Herein we see illustrated the great law of organized activity,
that it is a simultaneity of opposite tendencies, as organized matter
is a synthesis of compositions and decompositions, always tending
towards equilibrium and disturbance, storing up energy and liberating
it. Unlike what is observed in unorganized matter, the conditions of
waste bring with them conditions of repair, and thus--within certain
limits--every loss in one direction is compensated by gain in another.
There is a greater flow of nutrient material, or, more properly
speaking, a greater assimilation of it by the tissue, where there has
been made a greater opening for it by previous disintegration. The
alkaline state of the nutrient material, and the acid state of the
material that has been used,--the alkaline state which characterizes
repose and assimilation, and the acid state which characterizes
activity and deassimilation, are but cases of this general law; on the
synthesis of these opposite tendencies depends the restless change,
together with the continued specific integrity, of organized matter.
49. The state of organization may therefore be defined as the
_molecular union of the proximate principles of the three classes
in reciprocal dissolution_. An organism is formed of matter thus
organized, which exists in two states--the _amorphous_ and the
_figured_. The amorphous substances are liquid, semi-liquid, and solid;
the figured are the cells, fibres, and tubes, called “anatomical
elements.” For these I prefer the term suggested, I believe, by Milne
Edwards, namely, _organites_, because they are the individual elements
which mainly constitute the organs, and are indeed by many biologists
considered as elementary organisms. These organites, which go to form
the tissues, and by the tissues the organs, have their specific form,
volume, structure, and chemical reactions. They exist in textures
or tissues, or separately (e. g. blood corpuscles), and are in many
respects like the simplest organisms known, such as Monads, Vibrios,
Amœbæ, etc.
50. The simplest form of life is not--as commonly stated--a cell, but
a microscopic lump of jelly-like substance, or protoplasm, which has
been named _sarcode_ by Dujardin, _cytode_ by Haeckel, and _germinal
matter_ by Lionel Beale. This protoplasm, although entirely destitute
of texture, and consequently destitute of organs, is nevertheless
considered to be living, because it manifests the cardinal phenomena
of Life: Assimilation, Evolution, Reproduction, Mobility, and
Decay. Examples of this simplest organism are Monads, Protamœbæ,
and Polythalamia.[13] Few things are more surprising than the vital
activity of these organites, which puzzle naturalists as to whether
they should be called plants or animals. All microscopists are familiar
with the spectacle of a formless lump of albuminous matter (a Rhizopod)
putting forth a process of its body as a temporary arm or leg, or else
slowly wrapping itself round a microscopic plant, or morsel of animal
substance, thus converting its whole body into a mouth and a stomach;
but these phenomena are surpassed by those described by Cienkowski,[14]
who narrates how one Monad fastens on to a plant and sucks the
chlorophyll first from one cell and then from another; another Monad,
unable to make a hole in the cell-wall, thrusts long processes of its
body into the opening already made, and drags out the remains of the
chlorophyll left there by its predecessor; while a third Monad leads a
predatory life, falling upon other Monads that have filled themselves
with food. Here, as he says, we stand on the threshold of that dark
region where Animal Will begins; and yet there is here only the
simplest form of organization.[15]
51. Now let our glance pass on to the second stage--the Cell. Here we
have a recognized differentiation in the appearance of a nucleus amid
the protoplasm. The nucleus is chemically different from the substance
which surrounds it; and although perhaps exaggerated importance has
been attributed to this nucleus, and mysterious powers have been
ascribed to it, yet as an essential constituent of the cell it commands
attention. Indeed, according to the most recent investigations, the
definition of a cell is “a nucleus with surrounding protoplasm.” The
cell-wall, or delicate investing membrane--that which makes the cell a
closed sac--is no longer to be regarded as a necessary constituent, but
only as an accessory.[16]
52. The cell may be either an organism or an organite. It may lead an
isolated life as plant or animal, or it may be united with others and
lead a more or less corporate existence; but always, even as an element
of a higher organism, it preserves its own individuality. At first we
see that the corporate union is very slight, merely the contact of one
cell with another of its own kind, as in the filament of a Conferva.
Rising higher, we see the cell united with others different from
it; plants and animals appear, having structures composed of masses
of various cells. Rising still higher, we see animal forms of which
the web is woven out of myriads upon myriads of cells, with various
cell-products, processes, fibres, tubes.
ORGANISM AND MEDIUM.
53. But we have only one half of the great problem of life, when we
have the organism; and it is to this half that the chief researches
have been devoted, the other falling into neglect. What is that
other? The Medium in which the organism lives. Every individual
object, organic or inorganic, is the product of two factors:--first,
the relation of its constituent molecules to each other; secondly,
the relation of its substance to all surrounding objects. Its
properties, as an object or an organism, are the results of its
constituent molecules, and of its relation to external conditions.
Organisms are the results of a peculiar group of forces, exhibiting
a peculiar group of phenomena. Viewing these in the abstract, we
may say that there are three regulative laws of life:--(1) The _Lex
Formationis_--the so-called _nisus formativus_, or “organizing force”;
(2) the _Lex Adaptationis_, or adaptive tendency; (3) the _Lex
Hereditatis_, or tendency to reproduce both the original form and its
acquired modifications. We have always to consider the organizing
force in relation to all surrounding forces--a relation succinctly
expressed in the word Adaptation. Just as water is water only under a
certain relation of its constituent molecules to the temperature and
atmospheric pressure--just as it passes into other forms (ice or steam)
in adapting itself to other conditions; so, likewise, the organism only
preserves its individuality by the adjustment of its forces with the
forces which environ it.
54. This relation of Organism and Medium, the most fundamental of
biological data, has had a peculiar fortune: never wholly unrecognized,
for it obtrudes itself incessantly in the facts of daily experience,
it was very late in gaining recognition as a principle of supreme
importance; and is even now often so imperfectly apprehended that one
school of philosophers indignantly rejects the idea of the Organism and
Medium being the two factors of which Life is the product. Not only
is there a school of vitalists maintaining the doctrine of Life as an
entity independent both of Organism and Medium, and using these as its
instruments; but there is also a majority among other biologists, who
betray by their arguments that they fail to keep steadily before them
the fundamental nature of the relation. Something of this is doubtless
due to the imperfect conception they have formed of what constitutes
the Medium; instead of recognizing in it the sum of external conditions
affecting the organism--i. e. the sum of the relations which the
organism maintains with external agencies,--they restrict, or enlarge
it, so as to misapprehend its significance--restrict it to only a few
of the conditions, such as climate, soil, temperature, etc., or enlarge
it to embrace a vast array of conditions which stand in no directly
appreciable relation to the organism. Every one understands that an
organism is dependent on proper food, on oxygen, etc., and will perish
if these are withheld, or be affected by every variation in such
conditions. Every one understands that an animal which can devour or be
devoured by another, will flourish or perish according to the presence
of its prey or its enemy. But it is often forgotten that among external
existences, all those which stand in no appreciable relation to the
organism are not properly to be included in its Medium. In consequence
of this oversight we frequently hear it urged as an objection to the
Evolution Hypothesis, that manifold organisms exist under the _same_
external conditions, and that organisms persist unchanged amid a
great variety of conditions. The objection is beside the question. In
the general sum of external forces there are certain items which are
nearly related to particular organisms, and constitute their Medium;
those items which are so distantly related to these organisms as to
cause no reactions in them, are, for them, as if non-existent.[17] Of
the manifold vibrations which the ether is supposed to be incessantly
undergoing, only certain vibrations affect the eye as light; these
constitute the Medium of Sight; the others are as if they were not.
Only certain vibrations of the air affect the ear as Sound; to all
other vibrations we are deaf; though ears of finer sensibility may
detect them and be deaf to those which affect us.
55. “The external conditions of existence” is therefore the correct
definition of the Medium. An animal may be surrounded with various
foods and poisons, but if its organism is not directly affected by them
they cannot be food or poison to it. An animal may be surrounded with
carnivorous rivals, but if it is not adapted to serve them as food, or
is too powerful to be attacked by them, they only indirectly enter into
its Medium, by eating the food it would eat. The analogy is similar
with anorganisms and their relation to their media. Every physical or
chemical phenomenon depends on the concurrence of definite conditions:
namely, the substance which manifests the change, and the medium in
which the change is manifested. Alter the medium, solid, liquid, or
gaseous, change its thermal or electrical state, and the phenomenon is
altered. But although similar alterations in the medium notoriously
influence the organism, yet, because a great many variations in
external conditions are unaccompanied by appreciable changes in the
organism, there are biologists who regard this as a proof of Life being
independent of physical and chemical laws; an error arising from their
not recognizing the precise nature of organic conditions.
56. To give greater precision to the conception of a Medium it will
be desirable to adopt the distinction much insisted on by Claude
Bernard, namely, 1°, an External or Cosmical Medium, embracing the
whole of the circumstances outside the organism, capable of directly
affecting it, and 2°, an Internal or Physiological Medium, embracing
the conditions inside the organism, and in direct relation with
it--that is to say, the plasma in which its tissues are bathed, by
which they are nourished. To these add its temperature and electrical
conditions. Bernard only includes the nutritive fluid; but inasmuch as
each organism possesses a temperature and electrical state of its own,
and these are only indirectly dependent on the external temperature
and electricity, and as it is with these internal conditions that
the organism is in direct relation, I include them with the plasma
among the constituents of the Physiological Medium. Any change in the
External Medium, whether of temperature or electricity, of food or
light, which does not disturb the Internal Medium, will of course leave
the organism undisturbed; and for the most part all the changes in
the External Medium which do affect the organism, affect it by first
changing the Internal Medium. External heat or cold raises or depresses
the internal temperature _indirectly_ by affecting the organic
processes on which the internal temperature depends. We see here the
rationale of acclimatization. Unless the organism can adapt itself to
the new External Medium by the readjustment of its Internal Medium, it
perishes.
57. We are now enabled to furnish an answer to the very common
objection respecting the apparent absence of any direct influence of
external conditions. Let the objection first be stated in the words
of a celebrated naturalist, Agassiz: “It is a fact which seems to be
entirely overlooked by those who assume an extensive influence of
physical causes upon the very existence of organized beings, that the
most diversified types of animals and plants are everywhere found under
identical circumstances. The smallest sheet of fresh water, every
point of the sea-shore, every acre of dry land, teems with a variety
of animals and plants. The narrower the boundaries which are assigned
as the primitive home of all these beings, the more uniform must be
the conditions under which they must be assumed to have originated; so
uniform indeed that in the end the inference would be that the same
physical causes can produce the most diversified effects.”
Obviously there is a complete misstatement of the argument here; and
the excess of the misstatement appears in the following passage: “The
action of physical agents upon organized beings presupposes the very
existence of those beings.” Who ever doubted it? “The simple fact that
there has been a period in the history of our earth when none of these
organized beings as yet existed, and when, nevertheless, the material
constitution of our globe and the physical forces acting upon it were
essentially the same as they are now, shows that these influences are
insufficient to call into existence any living being.”[18] Although
most readers will demur to the statement that because the material
constitution of our globe was “essentially the same” before and after
animal life appeared, therefore there could have been no special
conditions determining the appearance of Life, the hypothesis of
Evolution entirely rejects the notion of organic forms having been
diversified by diversities in the few physical conditions commonly
understood as representing the Medium. Mr. Darwin has the incomparable
merit of having enlarged our conception of the conditions of existence
so as to embrace _all_ the factors which conduce to the result. In
his luminous principle of the Struggle for Existence, and the Natural
Selection which such a struggle determines, we have the key to most of
the problems presented by the diversities of organisms; and the Law of
Adaptation, rightly conceived, furnishes the key to all organic change.
58. In consequence of the defective precision with which the phrase
“Medium,” or its usual equivalent “physical conditions,” is employed,
several biological errors pass undetected. Haeckel[19] calls attention
to the common mistake of supposing the organism to be passive under the
influence of external conditions, whereas every action, be it of light
or heat, of water or food, necessarily calls forth a corresponding
reaction, which manifests itself in a modification of the nutritive
process. He points out the obverse of this error in the current notion
that Habit is solely due to the spontaneous action of the organism,
in opposition to the influence of external agency,--as if every
action were not the response to a stimulus. Corresponding with the
fluctuations in the Medium there must necessarily be fluctuations of
Adaptation, and I think we may safely assume that it is only when these
fluctuations cease that the Adaptation becomes Habit. This is the
interpretation of the phrase “Habit is _second_ Nature,” and is very
different from the common interpretation which attributes it to the use
or disuse of organs; as if use or disuse were a spontaneous uncaused
activity.
59. The organism, simple or complex, is, we have already seen, built
up from materials originally derived from the External Medium, but
proximately from the Internal Medium. This statement, however, requires
some qualification, especially in view of the hypothesis that organized
substance was originally created such as we now find it, and not
evolved from inorganic materials. Whether this hypothesis be adopted,
or rejected, we have the fact that the immense majority of organisms
_now_ existing--if not all--are products of pre-existing organisms;
and therefore organized matter is now mainly, if not solely, formed by
organized matter.
We take, therefore, as our point of departure, the protoplasm; this
is the first of the three terms of the vital synthesis: Structure,
Aliment, and Instrument. The evolution of this is proximately
dependent on the _pabulum_ afforded it in the Internal Medium, which
is the true nutrient material, and to which what is usually called
_food_ stands in an external relation: for between the reception of
food and its assimilation by the organite, there is an indispensable
intermediary stage, through which matter passes from the unorganized
to the organized state. This intermediate is now recognized in plants
as in animals. The old belief that plants were nourished _directly_
from the soil and atmosphere can no longer be sustained. The process
of Nutrition is alike in both: in both the materials drawn from the
External Medium are formed into proximate principles and organic
substances. It is daily becoming more and more probable that the
inorganic materials, water and oxygen, so freely entering into the
organism, never pass directly from the External Medium to the tissues,
but have to pass through the Internal Medium where they are changed,
so that the water is no longer free, but exists in a fixed state
which has no analogue out of the living substance. Only a part of
the water can be pressed out mechanically; the rest--that which is
already incorporated with the other elements--can only be got rid
of in a vacuum and at a high temperature. Oxygen, also, comports
itself differently in the tissue; as is proved by the fact that its
physiological absorption is markedly different from any chemical
oxidation in a dead or decomposing tissue.[20] Be this as it may, we
know that organic substances have to be unbuilt and rebuilt in the
organism; that the albumen of our food never passes directly into
the albumen of our tissues; any more than the milk drunk by a nursing
mother will pass into her breasts, and increase her supply, except by
nourishing her.
60. In the First Series of these Problems the term Bioplasm was
employed to designate this organized part of the Internal Medium. I
was led to adopt it as a corresponding term to that of Psychoplasm,
by which I wished to designate the _sentient_ material of the
psychological medium. There can be little doubt that the term Bioplasm
was an unconscious reproduction of the title of Dr. Beale’s work,
which I must have seen advertised. I withdraw it now that I have read
Dr. Beale’s work, and see that the signification he attaches to the
term is almost identical with Protoplasm. In lieu thereof, the term
Plasmode (from _plasma_, anything formed, and _odos_, a pathway) may
be substituted: it represents the _nutrient_ material on its way to
form Protoplasm, which is _formative_ material; while the materials
_formed_ may be termed Organites and Products: the organite being
the cell or cell-derivative (fibre, tube); the products being the
gaseous liquid and solid derivatives of vital processes, which are
_secretions_ when they form intercellular substance or return into the
plasmode and re-enter the vital circle; _excretions_ when they are
rejected, as incapable of further assimilation. The liver-cell will
furnish an example of each kind of product. The bile, though containing
principles serviceable in the chemical transformations, is for the
most part excreted; but besides bile, the liver-cell produces starchy
and saccharine principles which are true secretions, and re-enter the
plasmode.
61. The organite is thus composed of sap, substance, and product;
the organism, of plasmode, tissue, and product. A glance at the
vegetable-cell shows it to be constituted by the primordial utricle,
or protoplasm, the outermost layer of which is condensed into a
membrane, or cell-wall, and the cavity thus enclosed is filled with
sap. The cell-wall grows as the protoplasm grows, and the protoplasm
draws its material from the plasmode. A glance at the blood, the great
reservoir of the river of life, shows us plasmode in the serum, and
organites in the corpuscles; the one distinguished by sodic salts,
the other by potassic salts. The plasmode, or serum, is in a constant
change of composition and decomposition, giving up to the various
tissue-organites and intercellular plasmodes the requisite materials,
and receiving from organites and plasmodes the products of their
changes. The serum is fed from the food _and_ the tissues; and it feeds
the several plasmodes which bathe the several tissues. Passing into the
capillaries, it becomes transformed as it passes through their walls
into the intercellular spaces, saturating the acid products of the
cell-activities with its alkalies, and furnishing the protoplasms with
their needed materials.
62. It will be understood that, although in appearance these stages
are sharply defined, in reality they are insensible. But from the
analytical point of view we may regard Nutrition as the office
of the plasmode, and Evolution as the office of the protoplasm.
Although evolution or genesis of form depends on assimilation, it is
not a necessary consequence: the plasmode or the protoplasm might
preserve such perfect equality in the waste and repair, such complete
equilibrium, as not to undergo any development. The ova, for example,
which exist in the ovaries at birth are not all subsequently developed;
and if with modern embryologists we conclude that there is no
replacement of these by proliferation we shall in them have examples of
organites remaining unchanged through a period of fifty years.[21] But
such an equilibrium is perhaps only possible in complete inactivity.
63. Again, although the office of the plasmode is primarily that of
forming protoplasm, I think there is evidence to suggest that it not
only does this, but that some of it is used in the direct development
of energy, especially heat and electricity. The various forms of starch
and sugar taken in with the food or formed in the liver, certainly do
not as such enter into protoplasm. The same with alcohol.
64. It is perhaps in forgetfulness of the artificial nature of
analytical distinctions that controversies rage respecting what are
called intercellular substances and cell-walls. Now that the wall
is no longer regarded as an essential constituent of the cell, but
as a secondary formation, two opinions are maintained: first, that
it is merely a concentration of the external layer of protoplasm;
secondly, that it is a product of secretion from the protoplasm.
Both positions may be correct. Certainly in some cases there is no
other appreciable difference between wall and protoplasm than that
of a greater consistence; whereas in many other cases there exists a
decided difference in their chemical reactions, showing a difference
of composition. Taking both orders of fact, we may conclude that the
cell-wall is sometimes part of the organite, and sometimes product: a
blood-cell and a cartilage-cell may be cited as examples of each. And
this argument applies to the intercellular substance also.
65. The terms plasmode and protoplasm are general, and include many
species. There are different plasmodes for the different tissues,
so that we find phosphates of soda in the blood-serum, phosphates
of potash in the nerve-plasma, phosphates of magnesia in the
muscle-plasma, and phosphates of lime in the bone-plasma; having
severally to form the specifically different protoplasms of these
tissues. Observe, moreover, the gradations of these in respect of their
physical state: the blood being the most liquid, the nerve a degree
more solid, the muscle still more solid, and the bone almost entirely
solid; and since solubility of material is a necessary condition of
the chemical changes, we can understand how the blood, the nerve, the
muscle, and the bone represent degrees of vital activity: the greater
the instability of organized substance, the more active its molecular
renovation. Many serious errors result from overlooking the specific
differences of protoplasms; among them may be mentioned that very
common one of asserting that the ovum of a man is not distinguishable
from the ovum of any other mammal, nor the ovum of a mammal from that
of a reptile; nay, we sometimes see it stated that the protoplasm from
which a mammal may be developed is the same as that which is the germ
of an oak. So long as this simply asserts that we have at present no
means of distinguishing them by any chemical or physical tests, there
can be no objection raised; but it is a serious misconception, which
any embryological investigation ought to rectify, to suppose that the
ovum is not specific from the first.
66. Between the organites and their plasmodes there is the necessary
relation, which corresponds with the relation between organisms and
their mediums. Once formed, the organites are arranged side by side,
or end on end, into textures or tissues, and these are grouped into
organs, every organ being constituted by a collection of tissues, as
every apparatus is by a collection of organs, and the organism by the
federation of all the parts. We have more than once insisted on the
necessity of synthetic interpretation to complete the indications of
analysis: which means that no account of vital phenomena is _real_
unless it takes in all the co-operant factors, both those of the
organism and the medium. Neglect of this canon vitiates Dr. Beale’s
otherwise remarkable labors.
THE HYPOTHESIS OF GERMINAL MATTER.
67. It may help to elucidate certain important points if I here examine
the hypothesis which Dr. Beale has worked out with such patient skill,
but with what seem to me such unphysiological results. He deserves, I
think, more applause than has been awarded to him, not only for the
admirable patience with which he has pursued the idea, but also for
the striking definiteness of the idea itself--always a great advantage
in an hypothesis, since it gives precision to research. If biologists
have paid but little attention to it, this is no doubt due to the
theoretical, still more than to the observational contradictions it
presents. Histologists dispute his facts, or his interpretations;
while other biologists do not see their way in the application of
his hypothesis. Respecting all disputed points of observation I
shall be silent, for I have myself made no systematic researches in
this direction, such as would entitle me to form an estimate of the
evidence. But my dissent from the hypothesis is founded on biological
principles so fundamental that I should be willing to take my stand
entirely on the facts he himself puts forward.[22]
68. The hypothesis is that nothing in the organism has any claim
to vitality except the minute masses of protoplasm (by him called
bioplasm), which in the egg represent, he thinks, about the
one-thousandth part of the whole mass, the rest being lifeless matter,
namely, pabulum, and formed material. This bioplasm is the _germinal
matter_ out of which, by a _process of dying_, arise the tissues and
humors constituting the _formed material_--these, with the pabulum
which feeds the germinal matter, being all dead material. The germinal
matter itself, though living, only lives because there is temporarily
associated with it that Vital Force of which we have already spoken (§
14). In virtue of this association, a particle of matter not exceeding
the one hundred-thousandth of an inch in diameter is said to be alive;
and, presumably, to contain within it all those manifold powers which
the term Life condenses. The pabulum brought under the influence of
this Vital Force is transformed into germinal matter which, escaping
from this mysterious influence, _dies into tissue_. Muscle-fibres and
nerve-fibres are thus not living parts, nor are their actions vital. So
that, to be consistent, we must not speak of the organism as living,
but as a dead structure _produced_ by the Vital Force, and _set in
action_ by the aid of scattered bits of germinal matter. He has not, I
think, stated whether each of these bioplasms has its own Vital Force,
so that the organism is the theatre of millions of Vital Forces; or
whether it is one Vital Force which animates the whole organic world of
plants and animals. But nothing can be less equivocal than his position
respecting the lifelessness of every part of the organism except the
germinal matter.
69. The germinal matter may be selected as the primary stage of the
formed material, the initial point of growth, and thus stand for the
pre-eminently distinctive centre of Nutrition; but were we to limit all
Nutrition to the germinal matter, as defined by Dr. Beale, and deny
the co-operation of all the formed material, we should still not be
justified in restricting Life to simple Nutrition. We cannot exclude
such phenomena as those of Sensation and Motion, nor can we assign
these to the germinal matter.[23] To suppose this, would be equivalent
to saying that the steam which issues from a teakettle is capable of
the actions of a locomotive engine. The steam from the kettle is like
the steam from the boiler, it has molecular energy, and by this will
co-operate in the production of mechanical work, if the mechanism be
adjusted to it. The molecular energy of the protoplasm in muscular
fibre may be indispensable to the movements of the muscles, but these,
and not the protoplasmic movements alone, are muscular contractions. An
hypothesis, therefore, which is obliged to declare that muscle-fibre
and nerve-fibre are not living, even when active in the organism,
seems to me defective at its base. If we view these apart from the
organism, they may, like all the other formed materials, be regarded
as dead; and no one doubts that epidermis, nail, horn, hair, and bone
are dead in this sense, that they cannot live independently, and do not
reproduce themselves. But so long as even these form constituents of
the living organism, they also are _living_ (§ 42).[24] It is only by a
misconception of the analytical artifice that so simple a truth could
have been missed.
70. But this misconception meets us at many a turn. The Vitalist
hypothesis of an extra-organic agent of course refuses to regard Life
as the expression of all the co-operant conditions; and even opponents
of that hypothesis often fall into the same error of principle, when
they attempt to explain Life by localizing it in the cells; which is
simply a morphological substitution for the once popular doctrine that
only the vascular parts were organized, and every part destitute of
blood-vessels was dead. This idea seemed supported by the facts of the
most highly vascular parts being the most vital, and of a parallelism
existing between the vital activity of those organs which when injected
seemed almost entirely composed of blood-vessels, as the liver and
brain, and those which showed scarcely a trace of vessels, as cartilage
and bone; it seemed supported also by the appearance of blood-vessels
in all new formations, and by the idea of the blood as the nutrient
fluid. Then came the cell-doctrine, and the belief that the cell was
the really ultimate morphological element--which may be true--and that
“here alone there is any manifestation of life to be found, so that
we must not transfer the seat of vital action anywhere beyond the
cell,”[25]--which is very questionable.
71. We have already seen that the cell is an anatomical element, or
organite; the organism is but an aggregate of organites _and_ their
plasmodes. But Biology, which deals with the organism as a whole, and
with functions which are the resultants of all the vital properties,
must not be restricted to any single factor, however important.
It would assuredly be deemed absurd to say that diamond rings and
lead-pencils were the same, because the diamond and the plumbago,
which are the specific elements of each, are both the same chemical
element,--carbon. The substance is really different in diamond and
plumbago, is different in properties, and is, in rings and pencils,
united with different substances into objects having very different
properties. Whatever analysis may discover as to the identities of
organic structures, we cannot explain a single vital phenomenon
without taking into account the three terms, Structure, Aliment,
and Instrument; and whenever a cell is said to be the seat of vital
action, these three terms must be implied. In Dr. Beale’s hypothesis
the restriction is carried to its extreme; not content with the cell,
he withdraws vital action from the cell as a whole, assigning it to
the protoplasm and nucleus--cell-contents and cell-wall being, in his
view, dead. If it be true that the protoplasm is alone concerned in
Nutrition, yet Nutrition is not Life. Occupied mainly with formative
processes, it leaves other indispensable processes to other parts. He
instances the removal of all the tissues during the metamorphoses of
insects:--“new organs and textures are laid down afresh and developed
_ab initio_, instead of being built up upon those first formed.” But to
show how he restricts the idea of Life, he adds: “Such complete change,
however, necessitates a state of existence during which _action_ or
_function remains in complete abeyance_.”[26]
The muscles and nerves which are instrumental in this functional life
are said to be dead. It is true that the muscle-fibre does not develop
fresh fibres. But it is equally true that the protoplasm of muscle does
not alone execute _muscular_ contraction. Each has its special office.
Hence I reject the idea that formed material is dead. He further says
“formed material may _be_ changed, it cannot _change_ itself.” The
antithesis is doubly inexact: 1°, nothing changes itself, but only
yields to pressure, or reacts on being stimulated; and 2°, all the
evidence at hand is against the notion that the formed material is
not the seat of incessant molecular change; it is wasted and repaired
molecule by molecule. Kölliker properly protests against the growing
tendency of histologists to deify protoplasm, and to make it the sole
seat of vital changes, the cell-wall and cell-products having also, he
says, their physiological importance. It is manifestly erroneous to
deny vital changes to the red blood-corpuscles on the ground of their
no longer containing germinal matter.[27]
72. The analytical view may separate certain parts as active, and
other parts as passive, and thus regard the cells as the seats of
vital activity, the intercellular substance as merely accessory and
instrumental; but the real or synthetical view must recognize both
parts as equally indispensable, equally vital. Take cartilage, for
instance, with its enormous preponderance of intercellular substance
(formed material), and consider how absolutely impossible any of its
uses would be were it reduced to the germinal matter of its corpuscles!
And so of all the tissues.
73. If formed material is not to be excluded from the living parts of
the organism, neither is the plasmode, out of which the germinal matter
arises, since here we have the nutritive changes in their highest
activity; and because the property of Nutrition is here most active,
the other property of Development is in abeyance. Dr. Beale holds that
pabulum necessarily becomes germinal matter; but when we come to treat
of Nutrition it will appear that this is not more true than that Food
necessarily becomes Tissue: some of it does; but much of it is used up
for heat and other purposes.
74. What is true and important in the distinction between germinal
matter and formed material is, that from the former onwards there is a
gradual process of devitalization, the older parts of every organite
and tissue approaching more and more to the state of inorganic matter.
But to show how vain is the attempt to restrict Vitality to any one
out of a complex of co-operant factors, we might set up a chemical
hypothesis to the effect that Vitality depends on phosphates, and
with it explain the phenomena quite as well as with the hypothesis of
germinal matter. For not only is it found that the productive quality
of a soil depends on its richness in phosphates, but, as Lehmann has
shown, wherever cells and fibres make their appearance phosphates
are found, even in the lowest organisms, which, however, contain but
little. Phosphates abound in seeds and ova, in muscles and ganglia,
and are deficient in the woody parts of plants and the elastic fibres
of animals. The infant absorbs phosphates in large quantities and
excretes them in small quantities. Nervous activity is accompanied
by the consumption of a third more phosphorus than accompanies
muscular activity. Phosphates are among the most energetic of organic
stimulants. But who would endow the phosphates with Vitality, on the
ground of their indispensable presence in all vital processes?
75. Life, as we saw, is the expression of the whole organism. Many of
the parts are incapable of manifesting any vital phenomena except in
connection with all the rest; and of those parts which may be separated
from the organism and continue to manifest some vital phenomena, none
are capable of manifesting all. When the connexus of the parts is
destroyed the organism is dead. Long after that cessation which we call
Death, there are still evidences of Vitality in some of the parts:
the heart will continue to beat, the glands will secrete, the hair
will grow, the temperature will still be above that of the surrounding
medium, the muscles will be excitable; these vital properties are
the activities of organized substances, and so long as the state of
organization is preserved they are preserved; but the Life, which
is the synthesis of all the vital properties, vanishes with the
destruction of that synthesis.
76. May we not generalize this, and say that every special form of
existence, organic or inorganic, is determined by the synthesis of its
elements? Atoms are grouped into molecules, molecules into masses,
masses into systems. Out of the textureless germinal membrane and
the yolk, with no additions from without except oxygen and heat,
are developed all the textures and organs of the chick; and this
chick weighs no more than the egg out of which it was evolved. The
development has been a succession of syntheses--epigenesis upon
epigenesis. We may, if we please, regard each organite, as it appears,
living its separate life, and each tissue its separate life; but we
must not confound under the same symbol modes of existence so widely
different as the activities of an organite, and the activities of an
organism constituted by millions of organites.
77. If therefore we cannot restrict Life to the processes of Nutrition,
Dr. Beale’s hypothesis, whatever value it may have as explaining
histogenesis, is quite unacceptable. Neither Vital Force nor Bioplasm
covers the whole ground. For the former there is no better evidence
than our ignorance of the real synthesis; for the latter the evidence
is positive in its nature, but its interpretation is questionable. Dr.
Beale selects as the germinal matter those portions of tissue which
are susceptible of being deeply stained by the carmine solution, the
formed material being only stained in a faint degree; the nucleus
and nucleolus are the portions of germinal matter which are most
deeply stained; and hence he concludes that the older the matter the
fainter will be its coloration. There is no dispute as to the value
of the staining process, invented by Gerlach, for the discrimination
of chemically different parts of a tissue; and Dr. Beale has made
excellent use of it in his researches.[28] But I altogether dispute
the conclusion that the staining process reveals the parts which are
exclusively vital; and for this reason: it depends solely on the acid
reaction of those parts; and we cannot divorce the acid from the
alkaline agencies, both being indispensable. Nay, it has been proved
that in the _living animal_ no organized substance can be stained. Lord
Godolphin Osborne first discovered, in 1856, that the protoplasm of
growing wheat was susceptible of coloration;[29] but Gerlach, in 1858,
found that this never took place in the _animal_ during life. He kept
tadpoles and intestinal worms for weeks in colored fluids, without a
single spot becoming stained; although no sooner did these animals die
than the staining began. Nor even when he injected the colored fluids
under the skin and into the stomach, was the slightest coloration
produced.[30]
To Gerlach’s testimony may be added that of Stein, who, in his
magnificent work on _Infusoria_, says that not only has no foreign
substance ever been found in the protoplasm of the _Opalina_, but
in the _Acineta_, and all the embryos of the higher Infusoria known
to him, he has been unable to color the living substance.[31] This
resistance of the living protoplasm is surely a serious objection
to the hypothesis that only those parts of the dead organism which
are stained were the truly vital parts. Ranke sums up the results
of his experiments thus: “They all show that the living cell resists
the imbibition of every substance which it cannot assimilate. It is
precisely the impossibility of staining the cell that proves this
conclusively, since every particle of carmine absorbed would have
revealed its presence.”
It is not to be supposed that Dr. Beale was unacquainted with Gerlach’s
experiments. He has at any rate so far qualified the statement of his
hypothesis as to admit that it is only after death that the germinal
matter is stained. “The living matter” (he says, _How to Work with the
Microscope_, p. 107) “possesses an acid reaction, or to speak more
correctly, an acid reaction is always developed immediately after its
death.” Now, since this acid reaction only presents itself after death,
and it is this which is revealed by the carmine, we have no right to
conclude that the carmine singles out the vital parts. Every one knows
that the living muscle and nerve, when in repose, present an alkaline
or faintly neutral reaction, and after excitation this is changed into
an acid reaction, which increases with the exhaustion of the tissue. In
strict logic, therefore--if we could logically apply such a test--it
is the unstained parts that ought to be called vital. But, in truth,
alkalinity and acidity are equally indispensable.
78. The main object of my bringing this question forward was to
illustrate the danger of being misled by analysis: a danger we shall
see to be very serious in psychological inquiries. The aid derived from
analysis need never be undervalued; all that we have to bear in mind is
that it is only a logical artifice, and that our real explanation must
always be synthetic. Because of the tendency to rely on analysis there
has been an imperfect discrimination of the profound difference between
ORGANISMS AND MACHINES;
and while on the one hand the legitimate striving of the biologist
to display the mechanism of organic actions has been denounced by a
certain school as Materialism and a hateful attempt to “rob Life of
its mystery,” there has been on the other hand a misconception of this
mechanism, as if its dependent actions were of the nature of machines,
that is to say, as if organized mechanisms were strictly comparable
with machines constructed of inorganic parts. No doubt the laws of
Mechanics are the same in both, for these are abstract laws which take
no account of concrete differences. But when elaborate parallels are
drawn up between steam-engines and animal organisms, the coal consumed
in the one likened to the food in the other, and the force evolved in
the combustion in both being the same, there is a complete obliteration
of all that specially distinguishes vital activity.
79. Between an organism and a machine there is the superficial
resemblance that both have a complex structure, and are constructed of
different and dependent parts. But underneath this resemblance there
is a radical diversity.[32] The arrangement of parts in the organism
is more than a _juxtaposition_, it is a _solidarity_, arising from
the fact of their being all differentiations from a common substance
which is a special combination of the three classes of proximate
principles. Thus they are not parts which have been _put together_, but
which have been _evolved_, each out of a pre-existing part, and each
co-operating in the very existence of the other. The machine is made
of independent and primarily unrelated parts; its integrity depends
on the continued preservation of the substance of each part; waste
is here destruction. The organism is constituted by interdependent
and primarily related parts; its integrity depends on the continued
destruction and renovation of their substance; waste is a condition of
vitality. The actions of the machine are _sub_ordinated; the actions
of an organism are _co_-ordinated. The lever moves a wheel, and the
wheel in moving liberates a spring, each transmitting a communicated
impulse, but otherwise each acts independently--no slight modification
in the structure or movement of the wheel will modify the structure or
the movements of the lever, no alteration in the tension of the spring
will affect the structure of the wheel. But in the organism all are
parts of one sympathetic whole; each reacts on each; each is altered
by the other. Not a nerve is stimulated, nor a muscle moved, but the
entire organism is affected. A condensation here is the cause of a
greater imbibition there. The injection of salt or sugar under the skin
of the frog’s leg will produce cataract in its eye. The activity of
a secreting cell in the ovary, or liver, alters the condition of the
brain; the activity of the brain will check the secretion of a gland,
or relax the sphincters of the bladder. When we observe the growth of
horns, or the appearance of the beard, concomitant with the secretion
of spermatic cells--and especially when we observe with these a
surprising change in the physical and moral capabilities and tendencies
of the organism--we understand how the remotest parts of this mechanism
are bound together by one subtle yet all-powerful tie. Nothing of
this is visible in a machine. In a machine the material is so far of
secondary importance that it may be replaced by materials of various
kinds: a pulley may be worked with a hempen cord, a silken cord, or an
iron chain; a wheel may be wood, iron, copper, brass, or steel; the
actions will in each case be similar. Not so the organic mechanism:
the slightest variation, either in composition or intimate structure,
will affect, and may frustrate the organic activity. It is only in the
skeleton that the specific character of the materials may be changed;
and here only in the substitution of one phosphate for another in the
solid masonry.[33]
80. Another marked characteristic of the organism is that it has a
connexus of actions, the simultaneous effect of a continuous evolution,
appearing in stages and ages. And in the animal organism there is a
_consensus_ as well as a _connexus_, through which there is evolution
of Mind; and in the Social Organism an evolution of Civilization.
This consensus forms an intermediate stage through which the animal
actions are sensitive as well as nutritive, and the nutritive are
regulated by the sensitive. It is obvious that nothing like this is to
be found in a machine; and we conclude, therefore, that any view of the
organism which regards its mechanism without taking in these cardinal
characteristics must be radically defective. We no more deny the
existence of mechanical phenomena in denying that the organism is like
a machine, than we deny the existence of chemical phenomena in denying
that Vitality is chemical.
CHAPTER IV.
THE PROPERTIES AND FUNCTIONS.
81. The terms Property and Function are not always used with desirable
precision. There is, however, a marked distinction between the property
which characterizes a tissue in whatever organ the tissue may be found,
and the function which is exhibited by an organ composed of several
tissues. We ought never to speak of a function unless we imply the
existence of a correlative organ; and it is therefore incorrect to
speak of the function of Nutrition, since _all_ the tissues nourish
themselves; but we may speak of certain organs as special instruments
in facilitating Nutrition. Thus also with respiration, usually, but not
accurately, spoken of as the function of the lungs; the lungs being
simply the most effective of the instruments by which the interchange
of gases (which also takes place in every tissue) is facilitated. If
by Respiration we mean Breathing, then, indeed, Respiration is the
function of the lungs; if we mean the absorption of oxygen and the
exhalation of carbonic acid, Respiration is a general property of
vital tissue. A fragment of muscle removed from the body respires, so
long as its organization is intact; but it does not _breathe_--it has
no accessory instruments, nor does it need them. The co-operation of
nerve centres, diaphragm, ribs, circulating system, etc., necessary
in the complex organism to bring the due amount of oxygen to the
tissues, and convey away the carbonic acid, is here needless. In
the ascending animal series we find this necessity growing with the
complexity of the organism. The whole skin respires in the amphibia,
and to some extent in man also: a frog will live for ten or fourteen
days after extirpation of its lungs, the skin respiring sufficiently
to keep up a feeble vitality. But the skin does not suffice; and, very
early, certain portions are specialized into organs (at first in the
shape of external gills, and finally as internal lungs), for the more
energetic, because more specialized, performance of this office. In the
simpler organisms the blood is easily reached by the air; therefore no
instrument is needed. In primitive societies the transport of goods is
effected by men and women carrying them; in civilized societies by the
aid of horses and camels, and wagons drawn by oxen; till finally these
are insufficient, and railways are created, whose power of transport
transcends the earlier methods, as the breathing of a mammal transcends
the respiration of a mollusc. Breathing is the special function of an
organ--the lungs (or more strictly, the thoracic apparatus)--as Railway
Transport is a special social function. Although each of the tissues
forming this organ can, and does, exhale carbonic acid and absorb
oxygen--and each of the railway servants can, and does, transport
objects to and from the locomotive--yet the main work is thrown upon
the special apparatus.
82. What is meant by properties of tissue and functions of organs
may be thus illustrated. Let us suppose ourselves investigating the
structure of a ship. We find it composed of various _materials_--wood,
iron, copper, hemp, canvas, etc.; and these under various
_configurations_ are formed into particular parts serving particular
purposes, such as deck, masts, anchor, windlass, chains, ropes, sails,
etc. In all these parts the materials preserve their properties; and
wherever wood or iron may be placed, whatever purpose the part may
serve, the properties of wood and iron are unaffected; and it is
through a combination of these properties that the part is effective;
while through the connection of one part with another the purpose
becomes realized. The purposes to which masts, ropes, or sails are
subservient may be called their functions; and these of course only
exist, _as such_, in the ship. It is the same with the organism. We
find it composed of various Tissues, and these are combined into
various Organs or Instruments.[34] The properties of Tissues remain
the same, no matter into what Organs they may be combined; they
preserve and exert their physical, chemical, and vital properties,
as wood and iron preserve their properties. Each Tissue has its
characteristic quality; and the Organ which is constructed out of a
combination of several Tissues, more or less modified, is effective
solely in virtue of these properties,[35] while the Function of that
organ comes into play through its combination with other organs. For
example, muscular tissue has a vital property which is characteristic
of it, Contractility; and muscles are organs constituted by this
tissue and several others;[36] such organs have the general function
of Contraction, but whether this shall be specially manifested in
the beating of the heart, the winking of the eyelid, the movement
of the chest, or the varied movements of the limbs, will depend on
the _anatomical connections_. The reader unfamiliar with Biology is
requested to pay very particular attention to this point; he will find
many obscurities dissipated if he once lays hold of the “principal
connections.”
82_a_. Although Bichat’s conception was of great value, it was
not sufficiently disengaged from the metaphysical mode of viewing
biological phenomena. Both he and his disciples will be found treating
Properties as entities, and invoking them as _causes_ of the phenomena
instead of recognizing them simply as abstract _expressions_ of the
phenomena. Readers of my First Series will remember how often I have
had occasion to point out this common error: men having baptized
observed facts with a comprehensive name, forget the process of
baptism, and suppose the name to represent a mysterious agency. The
fact that gases combine is expressed in the term affinity; and then
Affinity is understood to be the cause of the combinations. The fact
that bodies tend towards each other is called their gravitation, and
Gravitation is then said to cause the tendency. The doctrine of vital
properties has been thus misunderstood. While no one imagines that
he can operate on affinity otherwise than by operating on the known
conditions under which gases combine, many a biologist and physician
speaks as if he could operate on the Irritability of a tissue, or the
Co-ordination of muscles, by direct action on these abstractions.
Let it be therefore once for all expressly stated that by the property
of a tissue is simply meant the _constant mode of reaction of that
tissue under definite conditions_. The property is not a cause,
otherwise than the conditions it expresses are a cause. And these
conditions are first those of the organized structure itself, and
secondly those of the medium in which it lives. Oxygen unites with
Hydrogen to form water, but only under certain pressures; so likewise
muscles manifest Contractility on being stimulated (that is their mode
of reaction), but only under certain degrees of temperature, humidity,
and a certain chemical composition of the plasmode. The property is
so truly an expression of the co-operant conditions, that it is found
to vary with those conditions, and to vanish when they vary beyond a
certain limit.
An attempt has been made to restrict the notion of a property to an
ultimate fact. Whatever is not reducible to known conditions is to
be accepted as a property. Combustion, for example, is reducible to
the molecular combination of oxygen and some other gas; but this
combination itself is not reducible, and it is therefore christened
affinity. I cannot accept this view. Admitting our inability to say
_why_ gases combine under certain conditions (and in this sense all
facts are inexplicable and ultimate, unless we take the _how_ as
ample explanation of the _why_), I must still say that since affinity
itself depends on the co-operation of known conditions, it is not less
explicable than combustion. But the point is unimportant: what we have
here to settle is the meaning of a property of tissue,--and that is the
mode of reaction which that tissue manifests under constant conditions,
internal and external.
83. The evolution of Life is the evolution of special properties and
functions from general properties and functions. The organism rises in
power as it ramifies into variety. Out of a seemingly structureless
germinal membrane, by successive differentiations certain portions
are set apart for the dominant, or exclusive, performance of certain
processes; just as in the social organism there is a setting apart
of certain classes of men for the dominant or exclusive performance
of offices, which by their co-operation constitute Society. The
soldier fights, but ceases to build or reap, weave or teach; the
mason builds; the agriculturist sows and reaps; the priest and
thinker teach; the statesman governs. In simple societies each
does all, or nearly all; but the social life thus manifested is
markedly inferior to the energetic life of a complex society. So with
organisms. An amœba manifests the general properties of Nutrition,
Reproduction, Sensibility, and Movement. But it has no special organs,
consequently no special functions. The polype has a certain rudimentary
specialization of parts: it has a simple alimentary cavity, and
prehensile tentacles; and although by these it can seize and digest its
prey, it can only do so in a limited way--all the manifold varieties
and power of prehension and digestion observed in more complex
organisms are impossible with such organs as the polype possesses.
84. Differences of structure and connection necessarily bring about
corresponding differences in Function, since Function is the _directed
energy_ of the Properties of tissues. One organ will differ from
another in structure, as the liver from the pancreas, or the kidney
from the spleen; or one organ may closely resemble another but differ
from it only in _connections_, as a sensory and a motor nerve, or an
extensor and a flexor muscle. We must therefore always bear both points
in mind. Every modification, structural or connectional, is translated
by a corresponding modification in the office. The hand and the foot
show this well. The tissues are the same in both, the properties are
the same, and both have the same general function of Prehension; but
their morphological differences carry corresponding differences in
their uses.
Suppose we have a galvanic battery, we know that its electric force
may be variously applied. Two pieces of charcoal fixed to the ends of
its conducting wires give us the electric light; replacing the charcoal
by a telegraphic apparatus we can transmit a message from one continent
to the other; the wires dipped in a solution effect a chemical
decomposition, dipped into a mixture of gases they effect a chemical
composition. In these, and many other applications, the property of the
battery is constant; but the functions it subserves have varied with
the varying co-operants. So with the properties of tissue.[37] Not only
have we to bear in mind the organic connections of the tissues, but
also the relation of the organs to their media. Swimming and Walking,
for example, are both functions of the locomotive apparatus, but they
are specially differenced by the media in which the animal moves.
85. The properties of tissues are their peculiar modes of reaction, and
each tissue has its dominant characteristic, such as the Contractility
of the muscle, and the Neurility of the nerve. But there has of late
years sprung up a misleading conception, partly a consequence of the
cell-theory, and partly of the almost inevitable tendency of analysis
to disregard whatever elements it provisionally sets aside; this
conception is the removal of the property from its _tissue_, and the
localization of it in one of the _organites_--cell or fibre. This has
been conspicuously mischievous in the case of the nerve-cell, which has
been endowed with mysterious powers, and may be said to have usurped
the place of nerve-tissue. I shall have to speak of this in the next
problem. Here I only warn the student against the common error. The
properties of a tissue depend on the structure and composition of
that tissue, together with its plasmode and products; they vary as
these vary. To select any one element in this complex, and ascribe the
reaction of the tissue to that, is only permissible as a shorthand
expression.
86. What has just been expounded may be condensed in the following
biological law:--
_Identity of tissue everywhere implies identity of property; and
similarity of tissue corresponding similarity of property. Identity
of organic connection everywhere implies identity of function; and
similarity of organic connection similarity of function._
87. This law, first formulated by me in 1859, and then applied to the
interpretation of nervous functions, was so little understood that for
the most part it met with either decided denial or silent neglect;
no doubt because of the general disinclination to admit that the
properties and functions of the spinal cord could be _similar_ to those
of the brain, in correspondence with the similarity of their tissues
and organic connections. Even Professor Vulpian, who adopted it, as
well as my principal interpretations, hesitated, and relapsed into the
orthodox view in assigning three different properties to one and the
same tissue in cord, medulla oblongata, and cerebrum.[38] In the course
of our inquiries we shall so frequently have to invoke this law that I
earnestly beg the reader to meditate upon it, and ask himself upon what
other grounds, save those of structure and connection, the properties
and functions can possibly rest? If on no other, then similarity in
structure and connection by logical necessity involves similarity in
property and function.
DOES THE FUNCTION DETERMINE THE ORGAN?
88. Closely connected with this law, which simply formulates the
self-evident principle that _every action is rigorously determined by
the nature of the agent, and the conditions under which the act takes
place_, is the surprising question whether functions are dependent
upon organs, or organs dependent on functions?--a question which
sometimes takes this shape: Is Life the result of organization, or is
organization the result of Life?
The vitalist, who holds that Life is an extra-organic agent, is logical
in declaring organization to be the consequence of Life;[39] but there
are many organicists who conclude from certain facts that organs are
developed by functions, and that organization is a result of Life.
There seems, however, to be some equivoque here. I cannot otherwise
understand how Mr. Spencer should have written: “There is one fact
implying that Function must be regarded as taking the precedence of
Structure. Of the lowest rhizopods which present no distinctions
of parts, and nevertheless feed and grow and move about, Professor
Huxley has remarked that they exhibit Life without Organization.”[40]
The equivoque here arises from the practice of calling all living
bodies “organisms,” even those destitute of the differentiations
called organs; but if we substitute the term “living body” in lieu of
“organism,” the equivoque will disappear, and Function no longer seem
to precede Structure. Neither Mr. Spencer nor Mr. Huxley would affirm
that Life can be manifested without a living body; and every living
body must have a structure of some sort--unless by structure be meant
a special configuration of parts. The properties of a body, whether it
be simple or complex in structure, result from the properties of its
components; and the vital phenomena vary with these varying components.
The substance of a Rhizopod is indeed simple as compared with that of
higher organisms, but is complex as compared with anorganisms; and
corresponding with this simplicity of structure there is simplicity of
vital function.[41]
89. The _properties_ of steam are exhibited by the kettle on the fire,
no less than by the gigantic engine which animates a manufactory;
but the _uses_ of steam (the functions of the engine) vary with the
varying structure, and the applications of that structure to other
structures. Precisely analogous is the case of the organ and its
function, in relation to the living substance of which it is a peculiar
modification. Vital actions are manifested by a lump of protoplasm; but
these actions are as sharply demarcated from the actions of more highly
organized animals, as the phenomena of a steam-engine are from those of
a teakettle.
90. Mr. Spencer has nowhere defined what he means by Structure, nor
given a definition of Organ, and this neglect makes it difficult
rightly to appreciate his view. But whether we take structure to
signify the _substance_ of the living body, or the _differentiations_
of that substance into separate tissues and organs, in either case
the actions (functions) of which this structure is the agent must be
rigorously determined by it. Mr. Spencer has avowed this in declaring
that the “general physiologist may consider functions in their widest
sense as the correlatives of tissue.” Is this true in the widest sense
and not true in the narrowest? I am puzzled to find him insisting that
“function from beginning to end is the determining cause of structure.
Not only is this manifestly true where the modification of structure
arises by reaction from modification of function; but it is also
true where a modification of structure otherwise produced apparently
initiates a modification of function.” Such language would be
consistent were he a vitalist who believed in a Principle independent
of Matter which shapes matter into organic forms; but as a positive
thinker he can scarcely escape the admission that since Function is the
activity of the Agent (Function in the widest sense being the action
of the whole Organism, and in its narrowest sense the action of the
special Organ) there cannot be an _activity preceding the agent_. I
suspect that he does not always bear in mind the distinction between
Property and Function, and consequently is led into statements at
variance with the principles he professes. As far as I understand the
course of his thought, it runs somewhat thus: With the increased use
of an organ its volume may be increased, its structure altered; this
alteration will, by reaction, cause alterations in other organs, and
thus the result of a change in the habitual activities of an animal
will be an alteration in the arrangement of its parts.
91. We speak loosely of an organ being developed by increased activity;
but this is loose speech, and investigation shows that the organ is not
developed _by_, but accompanies the increased activity, every increment
of activity being necessarily preceded by a corresponding increment
of structure. This is evident _à priori_: the force manifested is
inherent in the structure manifesting it. Thus we ought not to say
“the vascular system furnishes good instances of the increased growth
that _follows_ increased function”; we ought to say, “that _permits_
increased function.” The muscle having a contractile power represented
by 10, expends, we will suppose, 7 units of force in its normal
activity, and these are replaced by its normal nutrition. If from an
extra demand upon it 9 units are expended, the muscle becomes fatigued,
if 10, exhausted, and it will no longer contract, the whole disposable
sum of its contractility being dissipated. During all these stages the
structure of the muscle--or to prevent all equivoque, let us say the
substance of the muscle--has been changing, not indeed in any degree
appreciable to the eye, but appreciable by the more decisive tests of
chemical and physiological reactions. Yet inasmuch as in the ordinary
course of things the waste is quickly repaired, the muscle in repose
once more regains its original state, once more represents 10 units of
contractility. Now let us consider what takes place when extra labor
is thrown upon the muscle, when exercise causes growth. At the outset
of a walking tour we may not be able to compass more than twenty miles
a day, at its close we manage thirty. Is it the increased activity
of the function which has caused this increase of structure? In one
sense, yes; but let us understand it. Had the increase of activity
been temporary, there would have been only a temporary increase of
structure. But when the ordinary expenditure of 7 units rises to 9,
on several successive days, this extra expenditure of tissue has had
to be met by an extra nutrition--i. e. more plasmode has been formed
and more protoplasm. It is a physiological law, easily explained,
that, within due limits, extra waste brings about extra repair: as the
channels are widened and multiplied, the _derived_ currents become
stronger, and the increased flow of nutrition which was temporary
becomes permanent, because this increase is no longer dependent on an
extra stimulus, but on an enlarged channel.[42] When the channels have
not become multiplied or enlarged, which must be the case whenever the
extra stimulus is fluctuating and temporary, the extra expenditure is
not followed by increased size of the muscle: the currents resume their
old directions, no longer being diverted.
92. Let the social organism furnish us with an illustration. At the
present moment there is a movement against the retail shopkeepers of
London in favor of Co-operative Stores. The stimulus of getting better
goods and cheaper, attracts the flow of custom from its old channels;
and if this continue a certain time the new arrangements will be so
thoroughly organized, and will work so easily, that Co-operative Stores
will to a great extent supplant the retail shops. But if from any
causes the stimulus slackens before this reorganization has passed from
the oscillating into the permanent stage--if the goods are not found
to be superior, or the cheapness not worth the extra trouble--the old
influences (aiding our indolence) which have been long and continuously
at work, will cause the social organism to resume its old aspect,
and the co-operative “varieties” will disappear, or exist beside the
ancient “species.”
In the one case as in the other a glance at the process is enough
to detect that the increase in the activity has been preceded by
a corresponding increase in the structure. The muscle has not been
enlarged _by_ extra activity, but _with_ it. The co-operative action
has grown with each additional co-operator. Looking at the cases from
afar we may justly say that development has been due to function; but
looking to the process we see that each increment of activity was
necessarily dependent on an increment of substance. When changes of
habit or adaptation are said to produce modifications in structures,
this is true in as far as one modification of structure necessarily
brings with it correlative modifications, the growth of one part
affecting the growth of all more or less; but we must remember that
to render the structure capable of new adaptations corresponding
modifications must have been going on. The retail shopkeepers might
securely laugh at the co-operative movement if the respectable families
would not or could not become co-operant. When Mr. Spencer urges that
“not only may leaf-stalks assume to a great degree the character of
stems when they have to discharge the functions of stems by supporting
many leaves, and very large leaves, but they may assume the characters
of leaves when they have to undertake the functions of leaves,” I would
ask if he is not reversing the actual process? The stem cannot assume
the functions of a leaf until it has first assumed the character of a
leaf. The assumptions of both must be gradual, and _pari passu_.
93. The hand is an organ, its function is prehension. The performance
of this function in any of its numerous applications is rigorously
limited by the structure of the hand--the bones, muscles, nerves,
circulating and absorbent vessels, connective tissue, fat, etc. Fatigue
the nerve, and the function will be feebly performed; exhaust it,
and the function ceases; diminish the action of the heart, tie an
artery, or vitiate the structure of the blood, and the function will
be correspondingly affected; stiffen the tendons, soften the bones,
diminish the synovial fluid, or increase the fat--in short, make _any_
alteration whatever in the structure of the hand, and an alteration
is necessarily produced in its function. So rigorously is function
dependent upon structure, that the hand of one man will execute
actions which are impossible to another. The hand of a baby is said to
be the same in structure as the hand of a man; and since the powers
(functions) of the two are notoriously different, we might rashly
conclude that here function was dissociated from structure. The case is
illustrative. In baby and man the structure is similar, not the same;
the resemblance is of kind, not of degree; and the function likewise
varies with the degree. The penny cannon which delights the child is
similar in structure to the ten-pounder which batters down walls; and
though, speaking generally, we may say that the function of both is to
fire gunpowder for human ends, no one expects the penny cannon to be
employed in warfare. In physiology, as in mechanics, the effect varies
with the forces involved.
There can be no doubt that an exaggerated activity will produce a
modification in the active organ, for this is only the familiar case of
increased growth with increased exercise, and this is the biological
meaning in which Function can be said not, indeed, to _create_, but to
_modify_ an existing Organ. Preceding the activity there must be the
agent. Every organ although having its special function has also the
properties of all the tissues which constitute it. The function is only
the synthesis of these properties to which a dominant tissue gives a
special character. The eye, for example, though specially characterized
by its retinal sensibility to light, is largely endowed with muscles,
and its movements are essential to Vision. The intestinal canal, again,
though specially characterized by its secretions for the decomposition
of food, has muscles which are essential to Digestion. In many animals,
especially vegetable-feeders, there is an exaggeration of the muscular
activity in certain parts of the intestinal canal which is only
possible through a corresponding development of the muscular tissue, so
that in some birds, crustaceans, and molluscs we find a gizzard, which
is wholly without a mucous membrane to secrete fluids, and which aids
Digestion solely by trituration.
94. Mr. Spencer, as I have already suggested, seems to have been
led into his view by not keeping distinctly present to his mind the
differences between Properties of tissue and Function, the activity
of an organ. “That function takes precedence of structure,” he says,
“seems implied in the definition of Life. If Life consist of inner
actions so adjusted as to balance outer actions--if the actions are
the _substance_ of Life, while the adjustment constitutes its _form_;
then may we not say that the actions formed must come before that which
forms them--that the continuous change which is the basis of function
must come before the structure which brings the function into shape?”
The separation of “actions formed” from “that which forms them” is
inadmissible. An action cannot come _before_ the agent: it is the
agent in act. The continuous change, which is the basis of Vitality,
is a change of molecular arrangements; and the organ which gives a
special _direction_ to the vital activity, e. g. which shapes the
property of Contractility into the function of Prehension, this organ
must itself be formed before it can manifest this function. It is true
that in one sense the organs are formed by, or are differentiated in,
a pre-existent organism; true that the general activity of living
substance must precede the special activity of any organ, as the
expansions of steam must precede any steam-engine action; but the
general activity depends on the general structure; and the special
actions on the special structures. If by Organization we are to
understand not simply organized substance, but a more or less complex
arrangement of that substance into separate organs, the question is
tantamount to asking whether the simplest animals and plants have life?
And to ask the question, whether Life precedes organic substance? is
tantamount to asking whether the convex aspect of a curve precedes
the concave! or whether the motions of a body precede the body! To
disengage ourselves from the complicated suggestions of such a word as
Life, let us consider one of the vital phenomena, Contraction. This
is a phenomenon manifested by simple protoplasm, and by the highly
differentiated form of protoplasm known as muscle. In one sense it
would be correct to say that Contractility as a general property of
tissue precedes Contraction, which is specialized in muscle. But
it would be absurd to say that _muscular_ contraction preceded the
existence of muscle, and formed it. The contractions of the protoplasm
are not the same as muscular contractions any more than the hand of
a baby is the same as a man’s; the general property which both have
in common depends on the substance both have in common; the special
property which belongs to the muscle depends on its special structure.
An infinite activity of the contractile protoplasm would be incompetent
to form a muscle, unless it were accompanied by that peculiar change in
structure which constitutes muscle. The teakettle might boil forever
without producing a steam-engine or the actions of a steam-engine. That
which is true of one function is true of all functions, and true of
Life, which is the sum of vital activities.
95. It is this haziness which made Agassiz “regret to observe that
it has almost become an axiom that identical functions presuppose
identical organs. There never was a more incorrect principle leading
to more injurious consequences.”[43] And elsewhere he argues that
organs can exist without functions. But this is obviously to pervert
the fundamental idea of an organ. “The teeth of the whale which never
eat through the gums, and the breasts of the males of all classes
of mammalia,” are cited by him as examples of such organs without
functions; but in the physiological significance of the term these are
not organs at all. It is no more to be expected that the breasts of
the male should act in lactation, than that the slackened string of a
violin should yield musical tones; but the breasts of the male may be
easily stimulated into yielding milk, and the slackened string of the
violin may be tightened so as to yield tone. Even the breasts of the
female do not yield milk except under certain conditions, and in the
absence of these are on a par with those of the male.
96. Organized substance has the general properties of Assimilation,
Evolution, Sensibility, and Contractility; each of the special
tissues into which organized substance is differentiated manifests a
predominance of one of these properties. Thus although the embryo-cells
all manifest contractility, it is only the specialized muscle-cell
which continues throughout its existence to manifest this property,
and in a dominant form; the muscle-cell also assimilates and develops,
but besides having these properties in common with all other cells, it
has the special property of contracting with an energy not found in
the others. All cells respire; but the blood-cells have this property
of absorbing oxygen to a degree so far surpassing that of any other
cell that physiologists have been led to speak of their containing a
peculiar respiratory substance. In like manner all, or nearly all,
the tissues contain _myeline_--which indeed is one of the chief
constituents of the yolk of eggs--but only in the white sheath of the
nerves is it detached and specialized as a tissue.
97. But while Sensibility and Contractility are general properties
of organized substance, specialized in special tissues; Sensation
and Contraction are functions of the organs formed by such tissues;
and these organs are only found in animal organisms. It is a serious
error, which we shall hereafter have to insist on, to suppose that
Sensation can be the property of ganglionic cells, or, as it is more
often stated, the property of the central gray matter. Sensation is
the function of the organism; it varies with the varying organ; the
sensation of Touch not being the same as the sensation of Sight, or of
Sound.
98. We may consider the organism under two aspects--that of Structure
and that of Function. The latter has two broad divisions corresponding
with the vegetal and animal lives; the one is Nutrient, the other
Efficient. The one prepares and distributes Food, the other distributes
Motion. Of course this separation is analytical. In reality the two are
interblended; and although the neuro-muscular system is developed out
of the nutritive system, it is no sooner developed than it plays its
part as Instrument in the preparation and distribution of Aliment.
This not being a treatise on Physiology, there can be no necessity for
our here considering the properties and functions in detail. What is
necessary to be said on Sensibility and Contractility will find its
place in the course of future chapters; for the present we will confine
ourselves to Evolution on account of its psychological, no less than
its physiological, interest.
CHAPTER V.
EVOLUTION.
99. That organized substance has the property of nourishing itself
by assimilating from its internal medium substances there present in
an unorganized state, and that this is followed by a development or
differentiation of structure, is familiar to every inquirer.
Every one who has pursued embryological researches, and in a lesser
degree every one who has merely read about them, must have been
impressed by this marvel of marvels: an exceedingly minute portion
of living matter, so simple in aspect that a line will define it,
passes by successive modifications into an organism so complex that a
treatise is needed to describe it; not only do the cells in which the
ovum and the spermatozoon originate, pass into a complex organism,
reproducing the forms and features of the parents, and with these
the constitutional peculiarities of the parents (their longevity,
their diseases, their mental dispositions, nay, their very tricks and
habits), but they may reproduce the form and features, the dispositions
and diseases, of a grandfather or great-grandfather, which had lain
dormant in the father or mother. Consider for an instant what this
implies. A microscopic cell of albuminous compounds, wholly without
trace of organs, not appreciably distinguishable from millions of other
cells, does nevertheless contain within it the “possibilities” of an
organism so complex and so special as that of a Newton or a Napoleon.
If ever there was a case when the famous Aristotelian notion of a
“potential existence” seemed justified, assuredly it is this. And
although we can only by a fallacy maintain the oak to be _contained_
in the acorn, or the animal contained in the ovum, the fallacy is so
natural, and indeed so difficult of escape, that there is no ground
for surprise when physiologists, on first learning something of
development, were found maintaining that the perfect organism existed
already in the ovum, having all its lineaments in miniature, and only
growing into visible dimensions through the successive stages of
evolution.[44] The preformation of the organism seemed an inevitable
deduction from the opinions once universal. It led to many strange,
and some absurd conclusions; among them, to the assertion that the
original germ of every species contained within it all the countless
individuals which in process of time might issue from it; and this in
no metaphysical “potential” guise, but as actual boxed-up existences
(_emboîtés_); so that Adam and Eve were in the most literal sense
progenitors of the whole human race, and contained their progeny
already shaped within them, awaiting the great accoucheur, time.
100. This was the celebrated “emboîtement” theory. In spite of obvious
objections it gained scientific acceptance, because physiologists could
not bring themselves to believe that so marvellous a structure as that
of a human organism arose by a series of successive modifications, or
because they could not comprehend how it was built up, part by part,
into forms so closely resembling the parent-forms. That many and
plausible reasons pleaded in favor of this opinion is evident in the
fact that illustrious men like Haller, Bonnet, Vallisneri, Swammerdamm,
Réaumur, and Cuvier, were its advocates; and if there is not a sigle
physiologist of our day who accepts it, or who finds any peculiar
difficulty in following the demonstrations of embryologists, how from
the common starting-point of a self-multiplying epithelial cell parts
so diverse as hairs, nails, hoofs, scales, feathers, crystalline lens,
and secreting glands may be evolved, or how from the homogeneous
germinal membrane the complex organism will arise, there are very
few among the scorners of the dead hypothesis who seem capable of
generalizing the principles which have destroyed it, or can conceive
that the laws of Evolution apply as rigorously to the animal and
vegetable _kingdoms_ as to the individual _organisms_. The illustrious
names of those who advocated the preformation hypothesis may serve to
check our servile submission to the authorities so loudly proclaimed as
advocates of the fixity of species. The more because the two doctrines
have a common parentage. The one falls with the other, and no array of
authorities can arrest the fall. That the manifold differentiations
noticeable in a complex organism should have been evolved from a
membrane wholly destitute of differences is a marvel, but a marvel
which Science has made intelligible. Yet the majority of those to
whom this has been made intelligible still find an impossibility in
admitting that the manifold forms of plant and animal were successively
evolved from equally simple origins. They relinquish the hypothesis of
preformation in the one case, and cling to it in the other. Evolution,
demonstrable in the individual history, seems preposterous in the
history of the class. And thus is presented the instructive spectacle
of philosophers laughing at the absurdities of “preformation,” and
yet exerting all their logic and rhetoric in defence of “creative
fiats”--which is simply the preformation hypothesis “writ large.”
101. It would not be difficult to show that the doctrine of
Epigenesis, with which Wolff forever displaced the doctrine of
Preformation, leads by an inevitable logic to the doctrine of universal
Evolution; and that we can no more understand the appearance of a
new organism which is not the modification of some already existing
organism, than we can understand the sudden appearance of a new organ
which is not the modification of some existing structure. In the one
case as in the other we may disguise the process under such terms as
creative fiat and preformation; but these terms are no explanations;
they re-state the results, they do not describe the process; whereas
Epigenesis describes the process as it passes under the eye of science.
102. If any reader of these pages who, from theological or zoölogical
suspicion of the Development Hypothesis, clings to the hypothesis
of a creative Plan which once for all arranged the organic world in
Types that could not change, will ask what rational interpretation can
be given to the succession of phases each embryo is forced to pass
through, it may help to give him pause. He will observe that _none_ of
these phases have any adaptation to the future state of the animal, but
are in positive contradiction to it, or are simply purposeless; whereas
all show stamped on them the unmistakable characters of _ancestral_
adaptations and the progressions of Organic Evolution. What does the
fact imply? There is not a single known example of a complex organism
which is not developed out of simpler forms. Before it can attain the
complex structure which distinguishes it, there must be an evolution of
forms similar to those which distinguish the structures of organisms
lower in the series. On the hypothesis of a Plan which prearranged
the organic world, nothing could be more unworthy of a supreme
intelligence than this inability to construct an organism at once,
without previously making several tentative efforts, undoing to-day
what was so carefully done yesterday, and _repeating for centuries the
same tentatives, and the same corrections, in the same succession_. Do
not let us blink this consideration. There is a traditional phrase much
in vogue among the anthropomorphists, which arose naturally enough from
the tendency to take human methods as an explanation of the divine--a
phrase which becomes a sort of argument--“The Great Architect.” But
if we are to admit the human point of view, a glance at the facts of
embryology must produce very uncomfortable reflections. For what should
we say to an architect who was unable, or being able was obstinately
unwilling, to erect a palace except by first using his materials in the
shape of a hut, then pulling it down and rebuilding them as a cottage,
then adding story to story and room to room, _not_ with any reference
to the ultimate purposes of the palace, but wholly with reference to
the way in which houses were constructed in ancient times? What should
we say to the architect who could not form a museum out of bricks
and mortar, but was forced to begin as if going to build a mansion:
and after proceeding some way in this direction, altered his plan
into a palace, and that again into a museum? Yet this is the sort of
succession on which organisms are constructed. The fact has long been
familiar; how has it been reconciled with Infinite Wisdom? Let the
following passage answer for a thousand:--“The embryo is nothing like
the miniature of the adult. For a long while the body in its entirety
and its details presents the strangest of spectacles. Day by day and
hour by hour the aspect of the scene changes, and this instability is
exhibited by the most essential parts no less than by the accessory
parts. One would say that Nature feels her way, and only reaches the
goal after many times missing the path,--on dirait que la nature
tâtonne et ne conduit son œuvre à bon fin qu’après s’être souvent
trompée.”[45] Writers have no compunction in speaking of Nature feeling
her way and blundering; but if in lieu of Nature, which may mean
anything, the Great Architect be substituted, it is probable that the
repugnance to using such language of evasion may cause men to revise
their conceptions altogether; they dare not attribute ignorance and
incompetence to the Creator.
103. Obviously the architectural hypothesis is incompetent to explain
the phenomena of organic development. Evolution is the universal
process; not creation of a direct kind. Von Baer, who very properly
corrected the exaggerations which had been put forth respecting the
identity of the embryonic forms with adult forms lower in the scale,
who showed that the mammalian embryo never was a bird, a reptile,
or a fish, nevertheless emphasized the fact that the mammalian
embryo passes through all the lower typical forms; so much so that,
except by their size, it is impossible to distinguish the embryos of
mammal, bird, lizard, or snake. “In my collection,” he says, “there
are two little embryos which I have omitted to label, so that I am
now quite incompetent to say to what class they belong. They may be
lizards, they may be small birds, or very young mammals; so complete
is the similarity in the mode of formation of the head and trunk.
The extremities have not yet made their appearance. But even if they
existed in the earliest stage we should learn nothing from them, for
the feet of lizards, mammals, and the wings of birds, all arise from
the same common form.” He sums up with his formula: “The special type
is always evolved from a more general type.”[46]
Such reminiscences of earlier forms are intelligible on the supposition
that originally the later form was a modification of the earlier form,
and that this modification is repeated; or on the supposition that
there was a similarity in the organic conditions, which similarity
ceased at the point where the new form emerged. But on no hypothesis
of creative Plan are they intelligible. They are useless structures,
failing even to subserve a temporary purpose. Sometimes, as Mr. Darwin
remarks, a trace of the embryonic resemblance lasts till a late age:
“Thus birds of the same genus, and of closely allied genera, often
resemble each other in their first and second plumage: as we see in
the spotted feathers in the thrush group. In the cat tribe most of the
species are striped and spotted in lines; and stripes or spots can
plainly be distinguished in the whelp of the lion and the puma. We
occasionally, though rarely, see something of this kind in plants....
The points of structure in which the embryos of widely different
animals of the same class resemble each other often have no direct
relation to their conditions of existence. We cannot, for instance,
suppose that in the embryos of the vertebrata the peculiar loop-like
courses of the arteries near the bronchial slits are related to similar
conditions in the young mammal which is nourished in the womb of its
mother, in the egg of a bird which is hatched in a nest, and in the
spawn of a frog under water.”
104. It would be easy to multiply examples, but I will content myself
with three. The tadpole of the Salamander has gills, and passes his
existence in the water; but the _Salamandra atra_, which lives high
up among the mountains, brings forth its young full-formed. This
animal never lives in the water. Yet if we open a gravid female, we
find tadpoles inside her with exquisitely feathered gills, and (as I
have witnessed) these tadpoles “when from the mother’s womb untimely
ripped,” if placed in water, swim about like the tadpoles of water
newts. Obviously this aquatic organization has no reference to the
future life of the animal, nor has it any adaptation to its embryonic
condition; it has solely reference to ancestral forms, it repeats a
phase in the development of its progenitors. Again, in the embryo of
the naked Nudibranch, we always observe a shell, although the animal
is without a shell, and there can be no purpose served by the shell in
embryonic life.[47] Finally, the human embryo has a tail, which is of
course utterly purposeless, and which, although to be explained as a
result of organic laws, is on the creative hypothesis only explained as
an adherence to the general plan of structure--a specimen of pedantic
trifling “worthy of no intellect above the pongo’s.”[48]
105. Humanly appreciated, not only is it difficult to justify the
successive stages of development, the incessant building up of
structures immediately to be taken down, but also to explain why
development was necessary at all. Why are not plants and animals
formed at once, as Eve was mythically affirmed to be taken from Adam’s
rib, and Minerva from Jupiter’s head? The theory of Evolution answers
this question very simply; the theory of Creation can only answer
it by affirming that such was the ordained plan. But the theory of
Evolution not only gives the simpler and more intelligible answer to
this question, it gives an answer to the further question which leaves
the theory of Creation no loophole except a sophism--namely, why the
formation of organisms is constantly being frustrated or perverted?
And, further, it gives an explanation of the law noticed by Milne
Edwards, that Nature is as economical in her means as she is prodigal
in her variation of them: “On dirait qu’avant de recourir à des
ressources nouvelles elle a voulu épuiser, en quelque sorte, chacun
des procédés qu’elle avait mis en jeu.”[49] The applause bestowed on
Nature for being economical is a curious transference to Nature of
human necessities. Why, with a whole universe at her disposal, should
Nature be economical? Why must she always be working in the same
groove, and using but a few out of the many substances at her command?
Economy is a virtue only in the poor. If Nature, in organic evolutions,
is restricted to a very few substances, and a very few modes of
combination, always creating new forms by modification of the old, and
apparently incapable of creating an organism at once, this must imply
an inherent necessity which is very unlike the free choice that can
render economy a merit.
106. There may indeed be raised an objection to the Development
Hypothesis on the ground that if the complex forms were all developed
from the simpler forms, we ought to trace the identities through all
their stages. If the fish developed into the reptile, the reptile
into the bird, and the bird into the mammal (which I, for one, think
questionable), we ought to find, it is urged, evidence of this passage.
And at one time it was asserted that the evidence existed; but this
has been disproved, and on the disproof the opponents of Evolution
take their stand. Although I cannot feel much confidence in the idea
of such a passage from Type to Type, and although the passage, if ever
it occurred, must have occurred at so remote a period as to leave
no evidence more positive than inference, I cannot but think the
teaching of Embryology far more favorable to it than to our opponents.
Supposing, for the sake of argument, that the passage did take place,
ought we to find the embryonic stages accurately reproducing the
permanent forms of lower types? Von Baer thinks we ought; and lesser
men may follow him without reproach. But it seems to me that he starts
from an inadmissible assumption, namely, that the development must
necessarily be in a straight line rather than in a multiplicity of
divergent lines. “When we find the embryonic condition,” he says,
“differing from the adult, we ought to find a corresponding condition
somewhere in the lower animals.”[50] Not necessarily. We know that
the mental development of a civilized man passes through the stages
which the race passed through in the course of its long history, and
the psychology of the child reproduces the psychology of the savage.
But as this development takes place under conditions in many respects
different, and as certain phases are hurried over, we do not expect
to find a complete parallel. It is enough if we can trace general
resemblances. Von Baer adds, “That certain correspondences should occur
between the embryonic states of some animals and the adult states of
others seems inevitable and of no significance(?). They could not fail,
since the embryos lie within the animal sphere, and the variations
of which the animal body is capable are determined for each type by
the internal connection and mutual reaction of its organs, so that
particular repetitions are inevitable.” A profound remark, to which I
shall hereafter have occasion to return, but its bearing on the present
question is inconclusive. The fact that the embryonic stages of the
higher animals resemble in general characters the permanent stages
of the lower animals, and very closely resemble the embryonic stages
of those animals, is all that the Development Hypothesis requires.
Nor is its value lessened by the fact that many of the details and
intermediate stages seem passed over in the development of the higher
forms, for the recapitulation can only be of outlines, not of details;
since there are differences in the forms, there must be differences in
their histories.
107. In the preceding observations the object has simply been to show
that the phenomena to be explained can be rationally conceived as
resulting from gradual Evolution, whereas they cannot be so rationally
interpreted on any other hypothesis. And here it may be needful to say
a word respecting Epigenesis.
The Preformation hypothesis, which regarded every organism as a simple
educt and not the product of a germ, was called by its advocates an
evolution hypothesis--meaning that the adult form was an outgrowth of
the germ, the miniature magnified. Wolff, who replaced that conception
by a truer one, called his, by contrast, Epigenesis, meaning that
there was not simply _out_-growth but _new_ growth. “The various
parts,” he says, “arise one _after_ the other, so that always one is
secreted from (_excernirt_), or deposited (_deponirt_) on the other;
and then it is either a free and independent part, or is only fixed
to that which gave it existence, or else is contained within it. So
that _every part is the effect of a pre-existing part, and in turn
the cause of a succeeding part_.”[51] The last sentence expresses
the conception of Epigenesis which embryologists now adopt; and
having said this, we may admit that Wolff, in combating the error
of preformation, replacing it with the truer notion of gradual and
successive formation, was occasionally open to the criticism made
by Von Baer, that he missed the true sense of Evolution, since the
new parts are not _added on_ to the old parts as new formations,
but _evolved from_ them as transformations. “The word Evolution,
therefore, seems to me more descriptive of the process than Epigenesis.
It is true that the organism is not preformed, but the course of its
development is precisely the course which its parents formerly passed
through. Thus it is the Invisible--the course of development--which is
predetermined.”[52] When the word Epigenesis is used, therefore, the
reader will understand it to signify that necessary succession which
determines the existence of new forms. Just as the formation of chalk
is not the indifferent product of any combination of its elements,
carbon, oxygen, and calcium, but is the product of only one series of
combinations, an evolution through necessary successions, the carbon
uniting with oxygen to form carbonic acid, and this combining with the
oxide of calcium to form chalk, so likewise the formation of a muscle,
a bone, a limb, or a joint has its successive stages, each of which
is necessary, none of which can be transposed. The formation of bone
is peculiarly instructive, because the large proportion of inorganic
matter in its substance, and seemingly deposited in the organic tissue,
would lead one to suppose that it was almost an accidental formation,
which might take place anywhere; yet although what is called
connective tissue will ossify under certain conditions, true bone is
the product of a very peculiar modification, which almost always needs
to be preceded by cartilage. That the formation of bone has its special
history may be seen in the fact that it is the last to appear in the
animal series, many highly organized fishes being without it, and all
the other systems appearing before it in the development of the embryo.
Thus although the mother’s blood furnishes all the requisite material,
the fœtus is incapable of assimilating this material and of forming
bone, until its own development has reached a certain stage. Moreover,
when ossification does begin, it generally begins in the skull (in
man in the clavicle); and the only approach to an internal skeleton
in the Invertebrates is the so-called skull of the Cephalopoda.
Not only is bone a late development, but cartilage is also; and
although it is an error to maintain that the Invertebrates are wholly
destitute of cartilage, its occasional presence having been fully
proved by Claparède and Gegenbaur, the rarity of its presence is very
significant. The animals which can form shells of chalk and chitine are
yet incapable of forming even an approach to bone.
108. Epigenesis depends on the laws of succession, which may be likened
to the laws of crystallization, if we bear in mind the essential
differences between a crystal and an organism, the latter retaining
its individuality through an incessant molecular change, the former
only by the exclusion of all change. When a crystalline solution
takes shape, it will always take a definite shape, which represents
what may be called the _direction_ of its forces, the polarity of
its constituent molecules. In like manner, when an organic plasmode
takes shape--crystallizes, so to speak--it always assumes a specific
shape dependent on the polarity of its molecules. Crystallographers
have determined the several forms possible to crystals; histologists
have recorded the several forms of Organites, Tissues, and Organs.
Owing to the greater variety in elementary composition, there is in
organic substance a more various polar distribution than in crystals;
nevertheless, there are sharply defined limits never overstepped, and
these constitute what may be called the specific forms of Organites,
Tissues, Organs, Organisms. An epithelial cell, for example, may be
ciliated or columnar, a muscle-fibre striated or non-striated, a
nerve-fibre naked or enveloped in a sheath, but the kind is always
sharply defined. An intestinal tube may be a uniform canal, or a canal
differentiated into several unlike compartments, with several unlike
glandular appendages. A spinal column may be a uniform solid axis, or
a highly diversified segmented axis. A limb may be an arm, or a leg, a
wing, or a paddle. In every case the anatomist recognizes a specific
type. He assigns the uniformities to the uniformity of the substance
thus variously shaped, under a history which has been similar; the
diversities he assigns to the various conditions under which the
processes of growth have been determined. He never expects a muscular
tissue to develop into a skeleton, a nervous tissue into a gland,
an osseous tissue into a sensory organ. He never expects a tail to
become a hand or a foot, though he sees it in monkeys and marsupials
serving the offices of prehension and locomotion. He never expects
to find fingers growing anywhere except from metacarpal bones, or an
arm developed from a skull. The well-known generalization of Geoffroy
St. Hilaire that an organ is more easily annihilated than transposed,
points to the fundamental law of Epigenesis. In the same direction
point all the facts of growth. Out of a formless germinal membrane we
see an immense variety of forms evolved; and out of a common nutritive
fluid this variety of organs is sustained, repaired, replaced; and
this not indifferently, not casually, but according to rigorous laws
of succession; that which precedes determining that which succeeds
as inevitably as youth precedes maturity, and maturity decay. The
nourishment of various organs from plasmodes derived from a common
fluid, each selecting from that fluid only those molecules that are
like its own, rejecting all the rest, is very similar to the formation
of various crystals in a solution of different salts, each salt
separating from the solution only those molecules that are like itself.
Reil long ago called attention to this analogy. He observed that if
in a solution of nitre and sulphate of soda a crystal of nitre be
dropped, all the dissolved nitre crystallizes, the sulphate remaining
in solution; whereas on reversing the experiment, a crystal of sulphate
of soda is found to crystallize all the dissolved sulphate, leaving the
nitre undisturbed. In like manner muscle selects from the blood its own
materials which are there in solution, rejecting those which the nerve
will select.
109. Nay, so definite is the course of growth, that when a limb or part
of a limb is cut off from a crab or salamander, a new limb or new part
is reproduced in the old spot, exactly like the one removed. Bonnet
startled the world by the announcement that the _Naïs_, a worm common
in ponds, spontaneously divided itself into two worms; and that when he
cut it into several pieces, each piece reproduced head and tail, and
grew into a perfect worm. This had been accepted by all naturalists
without demur, until Dr. Williams, in his “Report on British Annelida,
1851,” declared it to be a fable. In 1858, under the impulse of Dr.
Williams’s very emphatic denial, I repeated experiments similar to
those of Bonnet, with similar results. I cut two worms in half, and
threw away the head-bearing segments, placing the others in two
separate vessels, with nothing but water and a little mud, which was
first carefully inspected to see that no worm lay concealed therein. In
a few days the heads were completely reformed, and I had the pleasure
of watching them during their reconstruction. When the worms were quite
perfect, I again cut away their heads, and again saw these reformed.
This was repeated, till I had seen four heads reproduced; after which
the worms succumbed.
110. The question naturally arises, Why does the nutritive fluid
furnish only material which is formed into a part like the old one,
instead of reproducing another part, or one having a somewhat different
structure? The answer to this question is the key to the chief problem
of organic life. That a limb _in situ_ should replace its molecular
waste by molecules derived from the blood, seems intelligible enough
(because we are familiar with it), and may be likened to the formation
of crystals in a solution; but how is it that the limb _which is not
in existence_ can assimilate materials from the blood? How is it that
the blood, which elsewhere in the organism will form other parts,
here will only form this particular part? There is, probably, no one
who has turned his attention to these subjects who has not paused to
consider this mystery. The most accredited answer at present before the
world is one so metaphysiological that I should pass it by, were it
not intimately allied with that conception of Species, which it is the
object of these pages to root out. It is this:
111. The organism is determined by its Type, or, as the Germans say,
its Idea. All its parts take shape according to this ruling plan;
consequently, when any part is removed, it is reproduced according to
the Idea of the whole of which it forms a part. Milne Edwards, in a
very interesting and suggestive work, concludes his survey of organic
phenomena in these words: “Dans l’organisme tout semble calculé en
vue d’un résultat déterminé, et l’harmonie des parties ne résulte
pas de l’influence qu’elles peuvent exercer les unes sur les autres,
mais de leur co-ordination sous l’empire d’une puissance commune,
d’un plan préconçu, d’une force pré-existante.”[53] This is eminently
metaphysiological. It refuses to acknowledge the operation of immanent
properties, refuses to admit that the harmony of a complex structure
results from the mutual relations of its parts, and seeks _outside_
the organism for some mysterious force, some plan, not otherwise
specified, which regulates and shapes the parts. Von Baer, in his great
work, has a section entitled, “The nature of the animal determines
its development”; and he thus explains himself: “Although every stage
in development is only made possible by the pre-existing condition
[which is another mode of expressing Epigenesis], nevertheless the
entire development is ruled and guided by the Nature of the animal
which is about to be (von der gesammten Wesenheit des Thieres welches
werden soll), and it is not the momentary condition which alone
and absolutely determines the future, but more general and higher
relations.”[54] One must always be slow in rejecting the thoughts
of a master, and feel sure that one sees the source of the error
before regarding it as an error; but in the present case I think the
positive biologist will be at no loss to assign Von Baer’s error to
its metaphysical origin. Without pausing here to accumulate examples
both of anomalies and slighter deviations which are demonstrably due
to the “momentary conditions” that preceded them, let us simply note
the logical inconsistency of a position which, while assuming that
_every separate stage_ in development is the necessary sequence of its
predecessor, declares the _whole of the stages_ independent of such
relations! Such a position is indeed reconcilable on the assumption
that animal forms are moulded “like clay in the hands of the potter.”
But this is a theological dogma, which leads to very preposterous and
impious conclusions; and whether it leads to these conclusions or to
others, positive Biology declines theological explanations altogether.
Von Baer, although he held the doctrine of Epigenesis, coupled it,
as many others have done, with metaphysical doctrines to which it is
radically opposed. He believed in Types as realities; he was therefore
consistent in saying, “It is not the Matter and its arrangements which
determine the product, but the nature of the parent form--the Idea,
according to the new school.” How are we to understand this Idea? If
it mean an independent Entity, an agency external to the organism, we
refuse to acknowledge its existence. If it mean only an _a posteriori_
abstraction expressing the totality of the conditions, then, indeed,
we acknowledge that it determines the animal form; but this is only an
abbreviated way of expressing the law of Evolution, by which each stage
determines its successor. The Type does not _dominate_ the conditions,
it _emerges_ from them; the animal organism is not cast in a mould, but
the imaginary mould is the form which the polarities of the organic
substance assume. It would seem very absurd to suppose that crystals
assumed their definite shapes (when the liquid which held their
molecules in solution is evaporated) under the determining impulse
of phantom-crystals, or Ideas; yet it has not been thought absurd to
assume phantom forms of organisms.
112. The conception of Type as a determining influence arises from
that fallacy of taking a resultant for a principle, which has played
so conspicuous a part in the history of philosophy. Like many others
of its class it exhibits an interesting evolution from the crude
metaphysical to the subtle metaphysical point of view, which at last
insensibly blends into the positive point of view. At first the Type or
Idea was regarded as an objective reality, external to the organism it
was supposed to rule. Then this notion was replaced by an approach to
the more rational interpretation, the idea was made an internal not an
external force, and was incorporated with the material elements of the
organism, which were said to “endeavor” to arrange themselves according
to the Type. Thus Treviranus declares that the seed “dreams of the
future flower”; and “Henle, when he affirms that hair and nails grow in
virtue of the Idea, is forced to add that the parts endeavor to arrange
themselves according to this Idea.”[55] Even Lotze, who has argued
so victoriously against the vitalists, and has made it clear that an
organism is a vital mechanism, cannot relinquish this conception of
legislative Ideas, though he significantly adds, “these have no power
in themselves, but only in as far as they are grounded in mechanical
conditions.” Why then superfluously add them to the conditions? If
every part of a watch, in virtue of the properties inherent in its
substance, and of the mutual reactions of these and other parts,
has a mechanical value, and if the sum of all these parts is the
time-indicating mechanism, do we add to our knowledge of the watch, and
our means of repairing or improving it, by assuming that the parts have
over and above their physical properties the metaphysical “tendency”
or “desire” to arrange themselves into this specific form? When we
see that an organism is constructed of various parts, each of which
has its own properties inalienable from its structure, and its uses
dependent on its relation to other parts, do we gain any larger insight
by crediting these parts with desires or “dreams” of a future result
which their union will effect? That which is true in this conception of
legislative Ideas is that when the parts come together there is mutual
reaction, and the resultant of the whole is something very unlike
the mere addition of the items, just as water is very unlike oxygen
or hydrogen; further, the connexus of the whole impresses a peculiar
direction on the development of the parts, and the law of Epigenesis
necessitates a serial development, which may easily be interpreted as
due to a preordained plan.
113. In a word, this conception of Type only adds a new name to the
old difficulty, adding mist to darkness. The law of Epigenesis,
which is simply the expression of the material process determined by
the polarity of molecules, explains as much of the phenomena as is
explicable. A lost limb is replaced by the very processes, and through
the same progressive stages as those which originally produced it. We
have a demonstration of its not being reformed according to any Idea
or Type which exists apart from the immanent properties of the organic
molecules, in the fact that it is not reformed at once, but by gradual
evolution; the mass of cells at the stump are cells of embryonic
character, cells such as those which originally “crystallized” into
muscles, nerves, vessels, and integument, and each cell passes through
all its ordinary stages of development. It is to be remembered that so
intimately dependent is the result on the determining conditions, that
any external influence which disturbs the normal course of development
will either produce an anomaly, or frustrate the formation of a new
limb altogether. One of my tritons bit off the leg of his female;[56]
the leg which replaced it was much malformed, and curled over the back
so as to be useless; was this according to the Idea? I cut it off, and
examined it; all the bones were present, but the humerus was twisted,
and of small size. In a few weeks a new leg was developed, and this
leg was normal. If the Idea, as a ruling power, determined the growth
of this third leg, what determined the second, which was malformed?
Are we to suppose that in normal growth the Idea prevails, in abnormal
the conditions? That it is the polarity of the molecules which at
each moment determines the group those molecules will assume, is well
seen in the experiment of Lavalle mentioned by Bronn.[57] He showed
that if when an octohedral crystal is forming, an angle be cut away,
so as to produce an artificial surface, a similar surface is produced
spontaneously on the corresponding angle, whereas all the other angles
are sharply defined. “Valentin,” says Mr. Darwin, “injured the caudal
extremity of an embryo, and three days afterwards it produced rudiments
of a double pelvis, and of double hind limbs. Hunter and others have
observed lizards with their tails reproduced and doubled. When Bonnet
divided longitudinally the foot of the salamander, several additional
digits were occasionally formed.”[58] Where is the evidence of the Idea
in these cases?
114. I repeat, the reproduction of lost limbs is due to a process which
is in all essential respects the same as that which originally produced
them; the genesis of one group of cells is the necessary condition
for the genesis of its successor, nor can this order be transposed.
But--and the point is very important--it is not every part that can be
reproduced, nor is it every animal that has reproductive powers. The
worm, or the mollusk, seems capable of reproducing every part; the crab
will reproduce its claws, but not its head or tail; the perfect insect
of the higher orders will reproduce no part (indeed the amputation of
its antennae only is fatal), the salamander will reproduce its leg,
the frog not. In human beings a muscle is said never to be reproduced;
but this is not the case in the rare examples of supplementary fingers
and toes, which have been known to grow again after amputation.
The explanation of this difference in the reproductive powers of
different animals is usually assigned to the degree in which their
organisms retain the embryonic condition; and this explanation is made
plausible by the fact that the animals which when adult have no power
of replacing lost limbs, have the power when in the larval state. But
although this may in some cases be the true explanation, there are
many in which it fails, as will be acknowledged after a survey of the
extremely various organisms at widely different parts of the animal
series which possess the reproductive power. Even animals in the same
class, and at the same stage of development, differ in this respect.
I do not attach much importance to the fact that all my experiments
on marine annelids failed to furnish evidence of their power of
reproducing lost segments; because it is difficult to keep them under
conditions similar to those in which they live. But it is significant
that, among the hundreds which have passed under my observation, not
one should have been found with a head-segment in the process of
development, replacing one that had been destroyed; and this is all the
more remarkable from the great tenacity of life which the mutilated
segments manifest. Quatrefages had observed portions of a worm, after
gangrene had destroyed its head and several segments, move about in the
water and avoid the light![59]
115. A final argument to show that the reproduction is not determined
by any ruling Idea, but by the organic conditions and the necessary
stages of evolution, is seen in the reappearance of a tumor or cancer
after it has been removed. We find the new tissue appear with all the
characters of the normal tissue of the gland, then rapidly assume one
by one the characters of the diseased tissue which had been removed;
and there as on is, that the regeneration of the tissue is accompanied
by the same abnormal conditions which formerly gave rise to the tumor:
the directions of “crystallization” are similar because the conditions
are similar. In every case of growth or regrowth the conditions being
the same, the result must be the same.
116. It seems a truism to insist that similarity in the results must be
due to similarity in the conditions; yet it is one which many theorists
disregard; and especially do we need to bear it in mind when arguing
about Species. I will here only touch on the suggestive topic of the
analogies observed not simply among animals at the extreme ends of the
scale, but also between animals and plants where the idea of a direct
kinship is out of the question.
My very imperfect zoölogical knowledge will not allow me to adduce a
long array of instances, but such an array will assuredly occur to
every well-stored mind. It is enough to point to the many analogies
of Function, more especially in the reproductive processes--to the
existence of burrowers, waders, flyers, swimmers in various classes--to
the existence of predatory mammals, predatory birds, predatory
reptiles, predatory insects by the side of herbivorous congeners,--to
the nest-building and incubating fishes; and in the matter of Structure
the analogies are even more illustrative when we consider the widely
diffused spicula, setæ, spines, hooks, tentacles, beaks, feathery
forms, nettling-organs, poison-sacs, luminous organs, etc.; because
these have the obvious impress of being due to a community of substance
under similar conditions rather than to a community of kinship. The
beak of the tadpole, the cephalopod, the male salmon, and the bird,
are no doubt in many respects unlike; but there is a significant
likeness among them, which constitutes a true analogy. I think there
is such an analogy between the air-bladder of fishes and the tracheal
rudiment which is found in the gnat-larva (_Corethra plumicornis_).[60]
Very remarkable also is the resemblance of the _avicularium_, or
“bird’s-head process,” on the polyzoon known popularly as the Corkscrew
Coralline (_Bugula avicularia_), which presents us in miniature
with a vulture’s head--two mandibles, one fixed, the other moved by
muscles visible within the head. No one can watch this organ snapping
incessantly, without being reminded of a vulture, yet no one would
suppose for a moment that the resemblance has anything to do with
kinship.
117. Such cases are commonly robbed of their due significance by being
dismissed as coincidences. But what determines the coincidence? If we
assume, as we are justified in assuming, that the _possible directions_
of Organic Combination, and the resultant forms, are limited, there
must inevitably occur such coincident lines: the hooks on a Climbing
Plant will resemble the hooks on a Crustacean or the claws of a Bird,
as the one form in which under similar external forces the more solid
but not massive portions of the integument tend to develop. I am too
ill acquainted with the anatomy of plants to say how the hooks so
common among them arise; but from examination of the Blackberry, and
comparison of its thorns with the hooks and spines of the Crustacea,
I am led to infer that in each case the mode of development is
identical--namely, the secretion of chitine from the cellular matrix of
the integument.
Another mode of evading the real significance of such resemblances
is to call them analogies, not homologies. There is an advantage in
having two such terms, but we ought to be very clear as to their
meaning and their point of separation. Analogy is used to designate
similarity in Function with dissimilarity in Structure. The wing
of an insect, the wing of a bird, and the wing of a bat are called
analogous, but not homologous, because their anatomical structure is
different: they are not constructed out of similar anatomical parts.
The fore-leg of a mammal, the wing of a bird, or the paddle of a
whale, are called homologous, because in spite of their diverse uses
they are constructed out of corresponding anatomical parts. To the
anatomist such distinctions are eminently serviceable. But they have
led to some misconceptions, because they are connected with a profound
misconception of the relation between Function and Organ. Embryology
teaches that the wing of the bird and the paddle of the whale are
developed out of corresponding parts, and that these are not like the
parts from which the wing of an insect or the flying-fish will be
developed; nevertheless, the most cursory inspection reveals that the
wing of a bird and the paddle of a whale are very unlike in structure
no less than in function, and that their diversities in function
correspond with their diversities in structure; whereas the wing of the
insect, of the bird, and of the bat, are in certain characters very
similar, and correspondingly there are similarities in their function.
It is, however, obvious that the resemblance in function is strictly
limited to the resemblance in anatomical structure; only in loose
ordinary speech can the flight of an insect, a bird, or a bat be said
to be “the same”: it is different in each--the weight to be moved, the
rapidity of the movement, the precision of the movements, and their
endurance, all differ.
NATURAL SELECTION AND ORGANIC AFFINITY.
118. It is impossible to treat of Evolution without taking notice
of that luminous hypothesis by which Mr. Darwin has revolutionized
Zoölogy. There are two points needful to be clearly apprehended before
the question is entered upon. The first point relates to the lax use
of the phrase “conditions,” sometimes more instructively replaced by
“conditions of existence.” Inasmuch as Life is only possible under
definite relations of the organism and its medium, the “conditions of
existence” will be those physical, chemical, and physiological changes,
which _in_ the organism, and _out_ of it, _co-operate_ to produce the
result. There are myriads of changes in the external medium which have
no corresponding changes in the organism, not being in any direct
relation to it (see § 54). These, not being co-operant conditions,
must be left out of the account; they are not conditions of existence
for the organism, and therefore the organism does not vary with their
variations. On the other hand, what seem very slight changes in the
medium are often responded to by important changes in the vital
chemistry, and consequently in the structure of the organism. Now the
nature of the organism at the time being, that is to say, its structure
and the physico-chemical state of its tissues and plasmodes, is the
main _condition_ of this response; the same external agent will be
powerful, or powerless, over slightly different organisms, or over the
same organism at different times. Usually, and for convenience, when
biologists speak of conditions, they only refer to external changes.
This usage has been the source of no little confusion in discussing
the Development Hypothesis. Mr. Darwin, however, while following the
established usage, is careful in several places to declare that of the
two factors in Variation--the nature of the organism and the nature of
the conditions--the former is by far the more important.
118_a_. A still greater modification of terms must now be made. Instead
of confining the “struggle for existence” to the competition of rivals
and the antagonism of foes, we must extend it to the competition and
antagonism of tissues and organs. The existence of an organism is not
only dependent on the external existence of others, and is the outcome
of a struggle; but also on the internal conditions which co-operate in
the formation of its structure, this structure being the outcome of a
struggle. The organism is this _particular_ organism, differing from
others, because of the particular conditions which have co-operated.
The primary and fundamental struggle must be that of the organic
forces at work in creating a structure capable of pushing its way
amid external forces. The organism must find a footing in the world,
before it can compete with rivals, and defend itself against foes.
Owing to the power of reproduction, every organism has a potential
indefiniteness of multiplication; that potential indefiniteness is,
however, in reality restricted by the supply of food, and by the
competition of rivals for that supply. The multiplication of any one
species is thus kept down by the presence of rivals and foes: a balance
is reached, which permits of the restricted quantities of various
species. This balance is the result of a struggle.
Now let me call attention to a similar process in the formation of the
organism itself. Every organite, and every tissue, has a potential
growth of indefinite extent, but its real growth is rigorously limited
by the competition and antagonism of the others, each of which has
its potential indefiniteness, and its real limits. Something, in the
food assimilated, slightly alters the part which assimilates it. This
change may be the origin of other changes in the part itself, or in
neighboring parts, stimulating or arresting the vital processes. A
modification of structure results. Or there may be no new substance
assimilated, but external forces may call a part into increased
activity--which means increased waste and repair; and this increase
here is the cause of a corresponding decrease somewhere else. Whatever
the nature of the change, it finds its place amid a complex of changes,
and its results are compounded with theirs. When organites and tissues
are said to have a potential indefiniteness of growth, there is
assumed a potential indefiniteness in the pabulum supplied: _if_ the
pabulum were supplied, and _if_ there were no antagonism thwarting its
assimilation, growth would of course continue without pause, or end;
but in reality this cannot be so. For, take the blood as the vehicle
of the pabulum--not only is its quantity limited, and partly limited
by the very action of the tissues it feeds, but even in any given
quantity there is a limit to its composition--it will only take up a
limited quantity of salts, iron, albumen, etc.; no matter how abundant
these may be in the food. So again with the plasmodes of the various
tissues--they have each their definite capacities of assimilation. What
has already been stated respecting chemical affinity (§ 20) is equally
applicable to organic affinity; as the presence of fused iron in the
crucible partially obstructs the combination of sulphur and lead, so
the presence of connective tissue partially obstructs the combination
of muscle protoplasm with its pabulum.
118 _b_. Owing to the action and reaction of blood and plasmode, of
tissues on tissues, and organs on organs, and their mutual limitations,
the growth of each organism has a limit, and the growth of each organ
has a limit. Beyond this limit, no extra supply of food will increase
the size of the organism; no increase of activity will increase the
organ. “Man cannot add a cubit to his stature.” The blacksmith’s arm
will not grow larger by twenty years of daily exercise, after it has
once attained a certain size. Increase of activity caused it to enlarge
up to this limit; but no increase of activity will cause it to pass
this limit. Why? Because here a balance of the co-operating formative
forces has been reached. Larger muscles, or more muscle-fibres, demand
arteries of larger calibre, and these a heart of larger size; with
the increase of muscle would come increase of connective tissue; and
this tissue would not only compete with the muscle for pabulum, but
by mechanical pressure would diminish the flow of that pabulum. And
why would connective tissue increase? Because, in the first place,
there is a formative association between the two, so that owing to a
law, not yet understood, the one always accompanies the other; and,
in the second place, there is a functional association between the
two, a muscle-fibre being _inoperative_ unless it be attached to a
tendon, or connective tissue; it will contract _out_ of the body
although separated from its tendon or other attachment; but _in_ the
body its contraction would be useless without this attachment. We must
bear in mind that muscle-fibres are very much shorter than ordinary
muscles; according to the measurements of W. Krause they never exceed
4 _cm_ in length, and usually range between 2 and 3 _cm_; their fine
points being fixed to the interstitial connective tissue, as the whole
muscle is fixed to its tendon. The function of the muscle is thus
dependent on a due balance of its component tissues; if that balance
is disturbed the function is disturbed. Should, from any cause, an
excess of muscle-fibre arise, the balance would be disturbed; should an
encroachment of connective tissue, or of fat, take place, there would
be also a defect of function.
Here we have the co-operation and limitation of the tissues
illustrated; let us extend our glance, and we shall see how the
co-operation and limitation of the organs come into play, so that
the resulting function depends on the balance of their forces. The
contractile power of each individual muscle is always limited by the
resistance of antagonists, which prevent the muscle being contracted
more than about a third of its _possible_ extent, i. e. possible when
there are no resistances to be overcome. Not only the increasing
tension of antagonist muscles, but the resistance of tendons, bones,
and softer parts must be taken into account. Thus, the increase of
the blacksmith’s muscular power would involve a considerable increase
in all the tissues of the arm; but such an increase would involve a
reconstruction of his whole organism.
Whenever there is an encroachment of one tissue on another, there
is a disturbance of the normal balance, which readily passes into a
pathological state. If the brain is overrun with connective tissue, or
the heart with fatty tissue, we know the consequences. If connective
tissue is deficient, epithelial runs to excess, no longer limited by
its normal antagonist, and pus, or cancer, result.
118_c_. It is unnecessary here to enlarge on this point. I have
adduced it to show that we must extend our conception of the struggle
for existence beyond that of the competition and antagonism of
organisms--the external struggle; and include under it the competition
and antagonism of tissues and organs--the internal struggle.
Variability is inherent in organic substances, as the result of
their indefiniteness of composition (§ 45_b_). This variability is
indefinite, and is rendered definite by the competition and antagonism,
so that every particular variation is the resultant of a composition
of forces. The forces in operation are the internal and external
conditions of existence--i. e. the nature of the organism, and its
response to the actions of its medium. A change may take place in
the medium without a corresponding response from the organism; or the
change may find a response and the organism become modified. Every
modification is a selection, determined by laws of growth; it is the
resultant of a struggle between what, for want of a better term, may
be called the _organic affinities_--which represent in organized
substances what chemical affinities are in the anorganized. Just as
an organism which has been modified and thereby gained a superiority
over others, has by this modification been _selected_ for survival--the
selection being only another aspect of this modification--so one
tissue, or one organ, which has surpassed another in the struggle
of growth, will thereby have become selected. Natural Selection,
or survival of the fittest, therefore, is simply the metaphorical
expression of the fact that any balance of the forces which is best
adapted for survival will survive. Unless we interpret it as a
shorthand expression of _all_ the internal and external conditions of
existence, it is not acceptable as the origin of species.
118_d_. Mr. Darwin has so patiently and profoundly meditated on the
whole subject, that we must be very slow in presuming him to have
overlooked any important point. I know that he has not altogether
overlooked this which we are now considering; but he is so preoccupied
with the tracing out of his splendid discovery in all its bearings,
that he has thrown the emphasis mainly on the external struggle,
neglecting the internal struggle; and has thus in many passages
employed language which implies a radical distinction where--as I
conceive--no such distinction can be recognized. “Natural Selection,”
he says, “depends on the survival under various and complex
circumstances of the best-fitted individuals, but has no relation
whatever to the primary cause of any modification of structure.”[61]
On this we may remark, first, that selection does not _depend_ on
the survival, but _is_ that survival; secondly, that the best-fitted
individual survives because of that modification of its structure
which has given it the superiority; therefore if the primary cause
of this modification is not due to selection, then selection cannot
be the cause of species. He separates Natural Selection from all the
primary causes of variation, either internal or external--either as
results of the laws of growth, of the correlations of variation, of
use and disuse, etc., and limits it to the slow accumulations of such
variations as are profitable in the struggle with competitors. And for
his purpose this separation is necessary. But biological philosophy
must, I think, regard the distinction as artificial, referring only
to one of the great factors in the production of species. And for
this reason: Selection only comes into existence in the modifications
produced either by external or internal changes; and the selected
change cannot be developed further by mere inheritance, unless the
successive progeny have such a disposition of the organic affinities
as will repeat the primary change. Inherited superiority will not by
mere transmission become greater. The facts which are relied on in
support of the idea of “fixity of species” show at any rate that a
given superiority will remain stationary for thousands of years; and
no one supposes that the progeny of an organism will vary unless some
external or internal cause of variation accompanies the inheritance.
Mr. Darwin agrees with Mr. Spencer in admitting the difficulty of
distinguishing between the effects of some definite action of external
conditions, and the accumulation through natural selection of inherited
variations serviceable to the organism. But even in cases where the
distinction could be clearly established, I think we should only see an
_historical_ distinction, that is to say, one between effects produced
by particular causes now in operation, and effects produced by very
complex and obscure causes in operation during ancestral development.
118_e_. The reader will understand that my criticism does not pretend
to invalidate Mr. Darwin’s discovery, but rather to enlarge its
terms, so as to make it include all the biological conditions, and
thus explain many of the variations which Natural Selection--in the
restricted acceptation--leaves out of account. Mr. Darwin draws a broad
line of distinction between Variation and Selection, regarding only
those variations that are favorable as selected. I conceive that all
variations which survive are by that fact of survival, _selections_,
whether favorable or indifferent. A variety is a species in formation;
now Selection itself is not a cause, or condition, of variation, it is
the _expression_ of variation. Mr. Darwin is at times explicit enough
on this head: “It may metaphorically be said that Natural Selection
is daily and hourly scrutinizing throughout the world the slightest
variations; rejecting those that are bad, preserving and adding up
all that are good; silently and insensibly working, whenever and
wherever opportunity offers, at the improvement of each organic being
in relation to its organic and inorganic conditions of life.”[62] But
the metaphorical nature of the term is not always borne in mind, so
that elsewhere Natural Selection is said to “act on and modify organic
beings,” as if it were a positive condition and not the expression
of the modifying processes. Because grouse are largely destroyed by
birds of prey, any change in their color which would render them less
conspicuous would enable more birds to escape; but it is obvious that
this change of color will be due to Organic Affinity; and only when
the change is _effected_ will there have been that selection which
_expresses_ it. Mr. Darwin’s language, however, is misleading. He
says: “Hence Natural Selection might be most effective in _giving_ the
proper color to each kind of grouse, and in _keeping_ that color when
once acquired.” This is to make Selection an agent, a condition of
the development of color; which may be accepted if we extend the term
so as to include the organic changes themselves. Again: “Some writers
have imagined that Natural Selection _induces variability_, whereas it
only implies the _preservation_ of such variations as are beneficial to
the being under its conditions of life.” It, however, is made to imply
more than this, namely, the accumulation and further modification of
such variations. “The mere existence of individual variability and of
some well-marked varieties, though necessary as the foundation, helps
us but little in understanding how species arise in nature. How have
all those exquisite adaptations of one part of the organization to
another part, and to the conditions of life, and of one organic being
to another being, been perfected?” My answer to this question would
be: By Organic Affinity, and the resulting struggle of the tissues and
organs, the consequences of which are that very _adaptation_ of the
organism to external conditions, which is expressed as the _selection_
of the structures best adapted. The selections are the results of the
struggle, according to my proposed extension of the term “struggle.”
Mr. Darwin defines the struggle: “The dependence of one being on
another, and including (what is more important) not only the life of
the individual but success in leaving progeny.” This definition seems
defective, since it omits the primary and more important struggle
which takes place between the organic affinities in operation. To
succeed in the struggle with competitors, the organism must have first
acquired--by selection--a superiority in one or more of its organs.
118_f_. A little reflection will disclose the importance of keeping
our eyes fixed on the internal causes of variation, as well as on the
external conditions of the struggle. Mr. Darwin seems to imply that the
external conditions which cause a variation are to be distinguished
from the conditions which accumulate and perfect such variation, that
is to say, he implies a radical difference between the process of
variation and the process of selection. This, I have already said, does
not seem to me acceptable; the selection, I conceive, to be simply the
variation which has survived.[63]
If it be true that a Variety is an incipient Species and shows
us Species in formation, it is in the same sense true that a
variation is an incipient organ. A species is the result of a slowly
accumulating divergence of structure; an organ is the result of a
slowly accumulating differentiation. At each stage of differentiation
there has been a selection, but we cannot by any means say that this
selection was determined by the fact of its giving the organism a
superiority over rivals, inasmuch as during all the early stages,
while the organ was still in formation, there could be no advantage
accruing from it. One animal having teeth and claws developed will
have a decided superiority in the struggle over another animal that
has no teeth and claws; but so long as the teeth and claws are in an
undeveloped state of mere preparation they confer no superiority.
118_g_. Natural Selection is only the expression of the results of
obscure physiological processes; and for a satisfactory theory of such
results we must understand the nature of the processes. In other words,
to understand Natural Selection we must recognize not only the facts
thus expressed, but the factors of these facts,--we must analyze the
“conditions of existence.” As a preliminary analysis we find _external
conditions_, among which are included not only the dependence of the
organism on the inorganic medium, but also the dependence of one
organism on another,--the competition and antagonism of the whole
organic world; and _internal conditions_, among which are included not
only the dependence of the organism on the laws of composition and
decomposition whereby each organite and each tissue is formed, but also
the dependence of one organite and one tissue on all the others--the
competition and antagonism of all the elements.
The changes wrought in an organism by these two kinds of conditions
determine Varieties and Species. Although many of the changes are due
to the process of natural selection brought about in the struggle
with competitors and foes, many other changes have no such relation
to the external struggle, but are simply the results of the organic
affinities. They may or they may not give the organism a greater
stability, or a greater advantage over rivals; it is enough that they
are no disadvantage to the organism, they will then survive by virtue
of the forces which produced them.
119. The position thus reached will be important in our examination
of the Theory of Descent by which Mr. Darwin tentatively, and his
followers boldly, explain the observed resemblances in structure and
function as due to blood-relationship. The doctrine of Evolution
affirms that all complex organisms are evolved by differentiation from
simpler organisms, as we see the complex organ evolved from simpler
forms. But it does not necessarily affirm that the vast variety of
organisms had one starting-point--one ancestor; on the contrary, I
conceive that the principles of Evolution are adverse to such a view,
and insist rather on the necessity of innumerable starting-points. Let
us consider the question.
That the Theory of Descent explains many of the facts must be admitted;
but there are many which it leaves obscure; and Mr. Darwin, with
that noble calmness which distinguishes him, admits the numerous
difficulties. Whether these will hereafter be cleared away by an
improvement in the Geological Record, now confessedly imperfect, or
by more exhaustive exploration of distant countries, none can say;
but, to my mind, the probability is, that we shall have to seek our
explanation by enlarging the idea of Natural Selection, subordinating
it to the laws of Organic Affinity. It does not seem to me, at present,
warrantable to assume Descent as the sole principle of morphological
uniformities; there are other grounds of resemblance beyond those of
blood-relationship; and these have been too much overlooked; yet a
brief consideration will disclose that similarity in the physiological
laws and the conditions of Organic Affinity must produce similarity
in organisms, independently of relationship; just as similarity in
the laws and conditions of inorganic affinity will produce identity
in chemical species. We do not suppose the carbonates and phosphates
found in various parts of the globe, or the families of alkaloids and
salts, to have any nearer kinship than that which consists in the
similarity of their elements and the conditions of their combination.
Hence, in organisms, as in salts, morphological identity may be due
to a community of conditions, rather than community of descent. Mr.
Darwin justly holds it to be “incredible that individuals identically
the same should have been produced through Natural Selection from
parents _specifically distinct_,” but he, since he admits analogous
variations, will not deny that identical forms might issue from parents
having widely different origins, provided that these parent forms
and the conditions of their reproduction were identical, as in the
case of vegetable and animal resemblances. To deny this would be to
deny the law of causation. And that which is true of identical forms
under identical conditions is true of similar forms under similar
conditions. When History and Ethnology reveal a striking uniformity in
the progression of social phases, we do not thence conclude that the
nations are directly related, or that the social forms have a common
parentage; we conclude that the social phases are alike because they
have had common causes. When chemists point out the uniformity of type
which exists in compounds so diverse in many of their properties as
water and sulphuretted or selenetted hydrogen, and when they declare
phosphoretted hydrogen to be the congener of ammonia, they do not mean
that the one is descended from the other, or that any closer link
connects them than that of resemblance in their elements.
In the case of vegetal and animal organisms, we observe such a
community of elementary substance as of itself to imply a community in
their laws of combination; and under similar conditions the evolved
forms must be similar. With this community of elementary substance,
there are also diversities of substance and of co-operant conditions;
corresponding with these diversities there must be differences of
form. Thus, although observation reveals that the bond of kinship does
really unite many widely divergent forms, and the principle of Descent
with Natural Selection will account for many of the resemblances and
differences, there is at present no warrant for assuming that all
resemblances and differences are due to this one cause, but, on the
contrary, we are justified in assuming a deeper principle which may be
thus formulated: All the complex organisms are evolved from organisms
less complex, as these were evolved from simpler forms; the link which
unites all organisms is not always the common bond of heritage, but the
uniformity of organized substance acting under similar conditions.
It is therefore consistent with the hypothesis of Evolution to admit a
variety of origins or starting-points, though not consistent to admit
the sudden appearance of complex Types, such as is implied in the
hypothesis of specific creations.
119 _a_. The analogies of organic forms and functions demand a more
exhaustive scrutiny than has yet been given them. Why is it that
vessels, nerves, and bones _ramify_ like branches, and why do these
branches take on the aspect of many crystalline forms? Why is it that
cavities are constantly prolonged in ducts, e. g. the mouth succeeded
by the œsophagus, the stomach by the intestines, the bladder by the
urethra, the heart by the aorta, the ovary by the oviduct, and so
on? Why are there never more than four limbs attached to a vertebral
column, and these always attached to particular vertebræ? Why is
there a tendency in certain tissues to form tubes, and in these tubes
commonly to assume a muscular coat?[64] To some of these queries an
answer might be suggested which would bring them under known physical
laws. I merely notice them here for the sake of emphasizing the fact
that such analogies lie deeply imbedded in the laws of evolution, and
that what has been metaphorically called organic crystallization will
account for many similarities in form, without forcing us to have
recourse to kinship. To take a very simple case. No one will maintain
that the crystalline forms of snow have any kinship with the plants
which they often resemble. Mr. Spencer has noticed the development
of a wing-bearing branch from a wing of the _Ptilota plumosa_, when
its nutrition is in excess. “This form, so strikingly like that of the
feathery crystallizations of many inorganic substances, proves to us
that in such crystallizations the simplicity or complexity of structure
at any place depends on the quantity of matter that has to be polarized
at that place in a given time. How the element of time modifies the
result, is shown by the familiar fact that crystals rapidly formed
are small, and that they become larger when they are formed more
slowly.”[65]
It may be objected, and justly, that in the resemblance between
crystals and organisms the analogy is purely that of form, and usually
confined to one element, whereas between organisms there is resemblance
of substance no less than of form, and usually the organisms are alike
in several respects. The answer to this objection is, that wherever
there is a similarity in the causal conditions (substance and history)
there must be a corresponding similarity in the results; if this
similarity extends to only a few of the conditions, the analogy will
be slight; if to several, deep. But whether slight or deep we are not
justified, simply on the ground of resemblance, in assuming, short of
evidence, that because they are alike, two organisms are related by
descent from a common ancestor.
120. Let us glance at a few illustrations. It has been urged as a
serious objection to Mr. Darwin’s hypothesis,[66] that it fails to
explain the existence of phosphorescent organs in a few insects; and
certainly, when one considers the widely different orders in which
these organs appear, and their absence in nearly related forms, it
is a difficulty. In noctilucæ, earthworms, molluscs, scolopendra,
and fireflies, we may easily suppose the presence of similar organic
conditions producing the luminosity; but it requires a strong faith to
assign Descent as the cause.[67] We may say the same of the electric
organs possessed by seven species of fish, belonging to five widely
separated genera. Although each species appears to have a limited
geographical range, one or the other is found in almost every part
of the globe. These organs occupy different positions, being now on
each side of the head, now along the body, and now along the tail;
and in different species they are innervated from different sources.
Their intimate structure also varies; as appears from the remarkable
investigations of Max Schultze.[68] They cannot, therefore, be
homologous. How could they have arisen? Not by the slow accumulations
of Natural Selection, because, until the organs were fully formed, they
could be of no advantage in the struggle; hence the slow growth of
the organ must have proceeded without the aid of an advantage in the
struggle--in each case from some analogous conditions which produced
a differentiation in certain muscles. The fundamental resemblance to
muscles was pointed out by Carus long ago. It has been insisted on by
Leydig:[69] and Owen says, “The row of compressed cells constituting
the electric prism of the Torpedo offers some analogy to the row of
microscopic discs of which the elementary muscle fibre appears to
consist.”[70] We must not, however, forget that these resemblances are
merely such as suggest that the electric organ is a _differentiation_
of the substance which elsewhere becomes muscular, and that Dr.
Davy was justified in denying the organ to be muscular.[71] That it
is substituted for muscle cannot be doubted. Now, although we are
entirely ignorant of the conditions which cause this differentiation of
substance which elsewhere becomes muscular, but here becomes electric
organs, we can understand that, when once such a development had
taken place, if it in any way profited the fish in its struggle for
existence, Natural Selection would _tend_ to its further increase and
propagation. So far Mr. Darwin carries us with him; but we decline
proceeding further. The development of these organs in fishes so widely
removed, does not imply an ancestral community. It is interpretable as
mere growth on a basis once laid; and therefore would occur with or
without any advantage in the struggle with rivals. The similarity in
concurrent conditions is quite enough to account for the resemblance
in structure. This, with his accustomed candor, Mr. Darwin admits. “If
the electric organs,” he says, “had been inherited from one ancient
progenitor thus provided, we might have expected that all electric
fishes would be specially related to each other. Nor does Geology at
all lead to the belief that formerly most fishes had electric organs
which most of their modified descendants have lost.”
121. It may seem strange that he should urge a difficulty against
his hypothesis when it could be avoided by the simple admission that
even among nearly allied animals great differences in development
are observable, and the electric organs might be ranged under such
diversities. But Mr. Darwin has so thoroughly wrought out his scheme,
that he foresees most objections, and rightly suspects that if this
principle of divergent development be admitted, it will cut the ground
from under a vast array of facts which his hypothesis of Descent
requires.
The sudden appearance of new organs, not a trace of which is
discernible in the embryo or adult form of organisms lower in the
scale,--for instance, the phosphorescent and electric organs,--is
like the sudden appearance of new instruments in the social organism,
such as the printing-press and the railway, wholly inexplicable
on the theory of Descent,[72] but is explicable on the theory of
Organic Affinity. For observe: if we admit that differentiations
of structure, and the sudden appearance of organs, can have arisen
spontaneously--i. e. not hereditarily--as the outcome of certain
changed physical conditions, we can hardly refuse to extend to the
whole organism what we admit of a particular organ. If, again, we
admit that organs very similar in structure and function spontaneously
appear in organisms of widely different kinds--e. g. the phosphorescent
and electric organs--we must also admit that similar resemblances may
present themselves in organisms having a widely different parentage;
and thus the admission of the spontaneous evolution of closely
resembling organs carries with it the admission of the spontaneous
evolution of closely resembling organisms: that the protoplasm of
muscular tissue should, under certain changed conditions, develop
into the tissue of electric organs, is but one case of the law that
organized substance will develop into organisms closely resembling each
other when the conditions have been similar.
122. It is to be remarked that Mr. Darwin fixes his attention somewhat
too exclusively on the adaptations which arise during the external
struggle for existence, and to that extent neglects the laws of organic
affinity; just as Lamarck too exclusively fixed his attention on the
influence of external conditions and of wants. Not that Mr. Darwin can
be said to overlook the organic laws; he simply underestimates the part
they play. Occasionally he seems arrested by them, as when instancing
the “trailing palm in the Malay Archipelago, which climbs the loftiest
trees by the aid of exquisitely constructed hooks, clustered around
the ends of the branches, and this contrivance no doubt is of the
highest service to the plant; but as there are nearly similar hooks
on many trees which are not climbers, the hooks on the palm may have
arisen from unknown laws of growth, and have been subsequently taken
advantage of by the plant undergoing further modification and becoming
a climber.”
123. I come round to the position from which I started, that the
resemblances traceable among animals are no proof of kinship; even a
resemblance so close as to defy discrimination would not, in itself,
be such a proof. The absolute identity of chalk in Australia and in
Europe is a proof that there was absolute identity in the formative
conditions and the constituent elements, but no proof whatever that the
two substances were originally connected by genesis. In like manner
the similarity of a plant or animal in Africa and Europe may be due
to a common kinship, but it may also be due to a _common history_. It
is indeed barely conceivable that the history, from first to last,
would ever be so rigorously identical in two parts of the globe as
to produce complex identical forms in both; because _any_ diversity,
either in structure or external conditions, may be the starting-point
of a wide diversity in subsequent development; and the case of organic
combinations is so far unlike the inorganic, that while only one form
is possible to the latter (chalk is either formed or not formed), many
forms are possible to organic elements owing to the complexity and
indefiniteness of organic composition. But although forms so allied as
those of Species are not readily assignable to an identical history
in different quarters of the globe, it is not only conceivable, but
is eminently probable, that Orders and Classes have no nearer link of
relationship than is implied in their community of organized substance
and their common history. The fact that there is not a single mammal
common to Europe and Australia is explicable, as Mr. Darwin explains
it, on the ground that migration has been impossible to them; but it
is also explicable on the laws of Evolution--to have had mammals of
the same species and genera would imply a minute coincidence in their
history, which is against the probabilities. Again, in the Oceanic
Islands there are no Batrachians; but there are Reptiles, and these
conform to the reptilian type. Mr. Darwin suggests that the absence of
Batrachia is due to the impossibility of migration, their ova being
destroyed by salt water. But may it not be due to the divergence
from the reptilian type, which was effected elsewhere, not having
taken place in these regions? When we find the metal Tin in Prussia
and Cornwall, and nowhere else in Europe, must we not conclude that
in these two countries, and nowhere else, a peculiar conjunction of
conditions caused this peculiar evolution?
124. The question at issue is, Are the resemblances observable
among organic forms due to remote kinship, and their diversities
to the divergences caused by adaptation to new conditions? or
are the resemblances due to similarities, and the diversities to
dissimilarities in the _substance and history_ of organic beings?
Are we to assume one starting-point and one centre of creation, or
many similar starting-points at many centres? So far from believing
that all plants and animals had their origin in one primordial cell,
at one particular spot, from which descendants migrated and became
diversified under the diverse conditions of their migration, it seems
to me more consistent with the principle of Evolution to admit a vast
variety of origins more or less resembling each other; and this initial
resemblance will account for the similarities still traceable under
the various forms; while the _early differences_, becoming intensified
by development under different conditions, will yield the diversities.
The evolution of organisms, like the evolution of crystals, or the
evolution of islands and continents, is determined, 1st, by laws
_inherent in the substances evolved_, and, 2d, by relations to the
medium in which the evolution takes place. This being so, we may
_à priori_ affirm that the resultant forms will have a community
strictly corresponding with the resemblance of the substances and
their conditions of evolution, together with a diversity corresponding
with their differences in substance and conditions. It is usually
supposed that the admission of separate “centres of creation” is
tantamount to an admission of “successive creations” as interpreted by
the majority of those who invoke “creative fiats.” But the doctrine
of Evolution, which regards Life as making its appearance _consequent
upon a concurrence of definite conditions_, and regards the specific
forms of Life as the necessary consequences of special circumstances,
must also accept the probability of similar conditions occurring at
different times and in different places. Upon what grounds, cosmical
or biological, are we to assume that on only _one_ microscopic spot of
this developing planet such a group of conditions was found--on only
one spot a particle of protein substance was formed out of the abundant
elements, and under conditions which caused it to grow and multiply,
till in time its descendants overran the globe? The hypothesis that
all organic forms are the descendants of a single germ, or of even
a few germs, and are therefore united by links of kinship more or
less remote, is not more acceptable than the hypothesis that all
the carbonates and phosphates, all the crystals, and all the strata
found in different parts of the globe, are the _descendants of a
single molecule_, or a few molecules; or,--since this may seem too
extravagant,--than that the various maladies which afflict organic
beings are, in a literal sense, members of _families_ having a nearer
relationship than that of being the phenomena manifested by similar
organs under similar conditions--a conception which might have been
accepted by those metaphysical pathologists who regarded Disease as
an entity. Few philosophers have any hesitation in supposing that
other planets besides our own are peopled with organic forms, though,
from the great differences in the conditions, these forms must be
extremely unlike those of our own planet. If separate worlds, why not
separate centres? The conclusion seems inevitable that wherever and
whenever the state of things permitted that peculiar combination of
elements known as organized substance, there and then a centre was
established--Life had a root. From roots closely resembling each other
in all essential characters, but all more or less different, there have
been developed the various stems of the great tree. Myriads of roots
have probably perished without issue; myriads have developed into forms
so ill-adapted to sustain the fluctuations of the medium, so ill-fitted
for the struggle of existence, that they became extinct before even our
organic record begins; myriads have become extinct since then; and the
descendants of those which now survive are like the shattered regiments
and companies after some terrific battle.
125. There seems to me only one alternative logically permissible to
the Evolution Hypothesis, namely, that all organic forms have had
either a single origin, or else numerous origins; in other words, that
a primordial cell was the starting-point from which all organisms
have been successively developed; or that the development issued
from many independent starting-points, more or less varied. This is
apparently not the aspect presented by the hypothesis to many of its
advocates; they seem to consider that if all organic forms are not the
lineal descendants of one progenitor, they must at any rate be the
descendants of not more than four or five. The common belief inclines
to one. Mr. Darwin, whose caution is as remarkable as his courage, and
whose candor is delightful, hesitates as to which conclusion should
be adopted: “I cannot doubt,” he says, “that the theory of descent,
with modifications, embraces all the members of the same class. I
believe that animals have descended from, at most, only four or five
progenitors, and plants from an equal or lesser number. Analogy would
lead me one step further, namely, to the belief that all animals and
plants have descended from some one prototype. But analogy may be a
deceitful guide.”
126. I cannot see the evidence which would warrant the belief that Life
originated solely in one microscopic lump of protoplasm on one single
point of our earth’s surface; on the contrary, it is more probable that
from innumerable and separate points of this teeming earth, myriads
of protoplast sprang into existence, _whenever_ and _wherever_ the
conditions of the formation of organized substance were present. It is
probable that this has been incessantly going on, and that every day
new protoplasts appear, struggle for existence, and serve as food for
more highly organized rivals; but whether an evolution of the lower
forms is, or is not, still going on, there can be no reluctance on
the part of every believer in Evolution to admit that when organized
substance was first evolved, it was evolved at many points. If this be
so, the community observable in organized substance, wherever found,
may as often be due to the fact of a common elementary composition as
to the fact of inheritance. If this be so, we have a simple explanation
both of the fundamental resemblances which link all organisms together,
and of the characteristic diversities which separate them into
kingdoms, classes, and orders. The resemblances are many, and close,
because the forms evolved had a similar elementary composition, and
their stages of evolution were determined by similar conditions.
The diversities are many, because the forms evolved had from the
first some diversities in elementary composition, and their stages of
evolution were determined under conditions which, though similar in
general, have varied in particulars. Indeed, there is no other ground
for the resemblances and differences among organic beings than the
similarities and dissimilarities in their Substance and History; and,
whether the similarities are due to blood-relationship, or to other
causes, the results are the same. There is something seductive in the
supposition that Life radiated from a single centre in ever-increasing
circles, its forms becoming more and more various as they came under
more various conditions, until at last the whole earth was crowded
with diversified existences. “From one cell to myriads of complex
organisms, through countless æons of development,” is a formula of
speculative grandeur, but I cannot bring myself to accept it; and I
think that a lingering influence of the tradition of a “creative fiat”
may be traced in its conception. May we not rather assume that the
earth at the dawn of Life was a vast germinal membrane, every slightly
diversified point producing its own vital form; and these myriads upon
myriads of forms--all alike and all unlike--urged by the indwelling
tendencies of development, struggled with each other for existence,
many failing, many victorious, the victors carrying their tents into
the camping ground of the vanquished. The point raised is the immense
improbability of organized substance having been evolved only in one
microscopic spot; if it were evolved at more than one spot, and under
slightly varying conditions, there would necessarily have arisen in
these earliest formations the _initial_ diversities which afterwards
determined the essential independence and difference of organisms.
129. Let us for a moment glance at the resemblances and diversities
observable in all organisms. All have a _common basis_, all being
constructed out of the same fundamental elements: carbon, hydrogen,
nitrogen, and oxygen; these (the organogens, as they are named),
with varying additions of some other elements, make up what we know
as Organic Substance, vegetal and animal. Another peculiarity all
organisms have in common, namely, that their matter is neither solid
nor liquid, but viscid. Beside this community of _Substance_ we must
now place a community of _History_. All organisms grow and multiply by
the same process; all pass through metamorphic stages ending in death;
all, except the very simplest, differentiate parts of their substance
for special uses, and these parts (cilia, membranes, tubes, glands,
muscles, nerves) have similar characters in whatever organism they
appear, and their development is always similar, so that the muscles or
nerves of an intestinal worm, a lobster, or a man, are in structure and
history fundamentally alike. When, therefore, we see that there is no
biological character of fundamental importance which is not universal
throughout the organic world, when we see that in Structure and History
all organisms have a community pervading every variety, it is difficult
not to draw the conclusion that some hidden link connects all organisms
into one; and when, further, it is seen that the most divergent forms
may be so arranged by the help of intermediate forms only slightly
varying one from the other, that the extreme ends--the monad and the
man--may be connected, and a genealogical tree constructed, which
will group all forms as modified descendants from a single form, the
hypothesis that kinship is the bidden link of which we are in search
becomes more and more cogent.
130. But now let the other aspect be considered. If there is
an unmistakable uniformity, there is also a diversity no less
unmistakable. The chemical composition of organic substances is
various. Unlike inorganic substances, the composition of which is
rigorously definite, organic substances are, within narrow limits,
variable in composition (§ 45).
I pass over the resemblances and differences observed in the earliest
stages of development, marked as they are, and direct attention to the
fact, that down at what must be considered the very lowest organic
region, we meet with differences not less striking than those met with
in the highest, we find structures (if structures they may be called),
which cannot be affiliated, so widely divergent is their composition.
The structureless vibrio, for example, is not only capable of living
in a medium destitute of Oxygen, but is, according to M. Pasteur,
actually killed by oxygen; whereas the equally simple bacteria can
no more dispense with Oxygen than other animals can. Consider for a
moment the differences implied in the fact that one organism cannot
even form an enveloping membrane to contain its protoplasm, whereas
another contrives to secrete an exquisite shell; yet between the
naked Rhizopod and the shelled Rhizopod our lenses and reagents fail
to detect a difference. One Monad can assimilate food of only one
kind, another Monad assimilates various kinds.[73] What a revelation
of chemical differences appears in the observations of M. Pasteur
respecting the vibrio and bacteria, in a fermentescible liquid--the
former beginning the putrid fermentation which the latter completes!
We cannot doubt that some marked difference must exist between the
single-celled organism which produces alcoholic fermentation, and that
which produces acetic fermentation, and that again which produces
butyric fermentation; and if we find distinctions thus established
at the lowest region of the organic series, we need not marvel if
the distinctions become wider and more numerous as the series becomes
more diversified. The structure and development of an organism are
dependent on the affinities of its constituent molecules, and it is
a biological principle of great importance which Sir James Paget
insists on, when he shows how “the existence of certain materials
in the blood may determine the formation of structures in which
they may be incorporated.”[74] _Any_ initial diversity may thus
become the starting-point of a considerable variation in subsequent
evolution.[75] Thus, supposing that on a given spot there are a dozen
protoplasts closely resembling each other, yet each in some one detail
slightly varying; if this variation is one which, by its relations to
the external medium, admits of a difference in the assimilation of
materials present in the medium, it may be the origin of some _new
direction_ in development, and the ultimate consequence may be the
formation of a shell, an internal skeleton, a muscle, or a nerve.
Were this not so, it would be impossible to explain such facts as
that chitine is peculiar to the Articulata, cellulose to Molluscoida,
carbonates of lime to Mollusca and Crustacea, and phosphates to
Vertebrata--all assimilated from the same external medium. But we
see that from this medium one organism selects the materials which
another rejects; and this selection is determined by the nature of the
structure: which assimilates only those materials it is _fitted_ to
assimilate. We hear a great deal of Adaptation determining changes of
structure and function, and are too apt to regard this process as if it
were not intimately dependent on a corresponding structural change. By
no amount of external influence which left the elementary composition
of the structure unchanged, could an organism with only two tissues
be developed into an organism with three or four. By no supply or
stimulus, could an animal incapable of assimilating peroxide of iron
acquire red blood corpuscles, although it might have the iron without
the corpuscles; nor could an oyster form its shell unless capable of
assimilating carbonate of lime. For myriads of years, in seas and
ponds, under endless varieties of external conditions, the amœbæ have
lived and died without forming a solid envelope, although the materials
were abundant, and other organisms equally simple have formed envelopes
of infinite variety. In all the seas, and from the earliest ages,
zoophytes have lived, and assumed a marvellous variety of shapes and
specialization of functions; but although some of them have acquired
muscles, none have acquired true nerves, none bone. Ages upon ages
rolled on before fishes were capable of forming bone; and thousands are
still incapable of forming it, though living in the same waters as the
osseous fishes.
131. “Looking to the dawn of life,” says Mr. Darwin (repeating an
objection urged against his hypothesis), “when all organic beings, as
we imagine, presented the simplest structure, how could the first steps
in advancement, or in the differentiation and specialization of parts
have arisen? I can make no sufficient answer; and can only say that,
as we have no facts to guide us, all speculation would be baseless and
useless.”
Where Mr. Darwin hesitates, lesser men need extra caution; but I
must risk the danger of presumption, at least so far as to suggest
that while an answer to this question is difficult on that dynamical
view of Evolution which regards Function as determining Structure,
it is less difficult on the statico-dynamical view propounded in
these pages; the difficulty which besets the explanation when all the
manifold varieties of organic forms are conceived as the successive
divergences from an original starting-point, is lessened when a variety
of different starting-points is assumed, in each of which some initial
diversity prepared the way for subsequent differentiations; just as
we know that between the ovum of a vertebrate and the ovum of an
invertebrate, similar as they are, there is a diversity which manifests
itself in their subsequent evolution. If Function is determined by
Structure, and Evolution is the product of the two, it is clear that
the different directions in the lines of development will have their
origin in structural differences, and not in the action of external
circumstances, unless these previously bring about a structural change.
The action of the medium on the organism is assuredly a potent factor
which Biology cannot ignore: but the organism itself is a factor, and
according to its nature the influence of the medium is defined. (§ 118.)
132. Quitting for a moment the track of this argument, let us glance
at the resemblances and differences observable in Plants and Animals,
because most people admit that these have separate origins. The
resemblances are scarcely less significant than those existing among
animals. Both have a similar basis of elementary composition; not only
are both formed out of protoplasts with similar properties, but in both
the first step from the protoplasm to definite structure is the Cell.
And the life of this Cell is remarkably alike in both, its phases of
development being in many respects identical; nay, even such variations
as obtain in the cell-membranes are curiously linked together by a
community in the formative process.[76] In both Plants and Animals
we find individuals constituted--1st, by single cells; 2d, by groups
of cells undistinguishable among each other; and 3d, by groups of
differentiated cells. In both we find colonies of individuals leading
a common life. In both the processes of Nutrition and Reproduction
are essentially similar; both propagate sexually and asexually; both
exhibit the surprising phenomena of parthenogenesis and alternate
generations. In both there are examples of a free-roving embryo which
in maturity becomes fixed to one spot, losing its locomotive organs
and developing its reproductive organs. In both the development of the
reproductive organs is the climax which carries Death. So close is the
analogy between plant-life and animal-life, that it even reaches the
properties usually held to be exclusively animal; I mean that even
should we hesitate to accept Cohn’s discovery of the muscles in certain
plants,[77] we cannot deny that plants exhibit Contractility; and
should we refuse to interpret as Sensibility the phenomena exhibited by
the Sensitive Plants, we cannot deny that they present a very striking
analogy to the phenomena of Sensibility exhibited by animals.
133. It is unnecessary to continue this enumeration, which might easily
be carried into minute detail. A chapter of such resemblances would
only burden the reader’s mind, without adding force to the conclusion
that a surprising community in Substance and Life-history must be
admitted between Plants and Animals. This granted, we turn to the
differences, and find them no less fundamental and detailed. Chemistry
tells us nothing of the differences in the protoplasms from which
animals and plants arise; but that initial differences must exist is
proved by the divergence of the products. The vegetable cell is not
the animal cell; and although both plants and animals have albumen,
fibrine, and caseine, the _derivatives_ of these are unlike. Horny
substance, connective tissue, nerve tissue, chitine, biliverdine,
creatine, urea, hippuric acid, and a variety of other products of
evolution or of waste, never appear in plants; while the hydrocarbons
so abundant in plants are, with two or three exceptions, absent from
animals. Such facts imply differences in elementary composition; and
this result is further enforced by the fact that where the two seem
to resemble, they are still different: the plant protoplasm forms
various cells, but never forms a cartilage-cell or nerve-cell; fibres,
but never a fibre of elastic tissue; tubes, but never a nerve tube;
vessels, but never a vessel with muscular coatings; solid “skeletons,”
but always from an organic substance (_cellulose_), not from phosphates
and carbonates. In no one character can we say that the plant and the
animal are identical; we can only point throughout the two kingdoms to
a great similarity accompanying a radical diversity.
134. Having brought together the manifold resemblances, and the no
less marked diversities, we must ask what is their significance? Do
the resemblances imply a community of origin, an universal kinship?
If so, the diversities will be nothing more than the divergences
which have been produced by variations in the Life-history of the
several groups. Or--taking the alternative view--do the diversities
imply radical differences of origin? If so, the resemblances will be
nothing more than the inevitable analogies resulting from Organized
Substance being everywhere somewhat similar in composition, and similar
in certain phases of evolution. To state the former position in the
simplest way, we may assume that of two masses of protoplasm having
a common parentage, one, by the accident of assimilating a certain
element not brought within the range of the other, thereby becomes so
differentiated as to form the starting-point of a series of evolutions
widely divergent from those possible to its congener; and at each stage
of evolution the introduction of a new element (made possible by that
stage) will form the origin of a new variation. It is thus feasible to
reduce all organic forms to a primordial protoplasm, in the evolutions
of which successive differentiations have been established. On the
other hand, it is equally feasible to assume that the existence of
radical differences must be invoked to account for the possibility of
the successive differentiations.
135. The hunt after resemblances has led to much mistaken speculation;
and with reference to the topic now before us, it may be urged,
that although by attaching ourselves to the points of community, in
disregard of the diversities, we may make it appear that all animals
have a common parentage, and that plants and animals are merely
divergent groups of the same prototype, a rigorous logic will force us
onwards, and compel us to admit that a kinship no less real unites
the organic with the inorganic world. For upon what principle are we
to pause at the cell or protoplasm? If by a successive elimination
of differences we reduce all organisms to the cell, we must go on
and reduce the cell itself to the chemical elements out of which it
is constructed; and inasmuch as these elements are all common to the
inorganic world, the only difference being one of synthesis, we reach a
result which is the stultification of all classification, namely, the
assertion of a kinship which is universal. We must bear in mind that
all things may be reduced to a common root by simply disregarding their
differences. All things are alike when we set aside their unlikeness.
136. Suppose, for the sake of illustration, we regard an Orchestra
in the light of the Development Hypothesis. The various instruments
of which it is composed have general resemblances and particular
differences, not unlike those observable in various organisms; and
as we proceed in the work of classification we quickly discover that
they may be arranged in groups analogous to the Sub-kingdoms, Classes,
Orders, Genera, and Species of the organic world. Each group has its
cardinal distinction, its initial point of divergence. All musical
instruments resemble each other in the fundamental character of
producing Tone by the vibrations of their substance. This may be called
their organic basis. The first marked difference which determines the
character of two sub-kingdoms (namely, instruments of Percussion and
Wind instruments) arises from a difference in the method of impressing
the vibrations; and the grand divisions of these sub-kingdoms arise
from the nature of the vibrating substances. Each type admits of many
modifications, but the primary distinction is ineffaceable. We can
conceive the Pipe modified into a Flute, a Flageolet, a Clarionet,
a Hautbois, a Bassoon, or a Fife, by simple accessory changes; to
modify the Pipe into a Trumpet, and thus produce the peculiar _timbre_
of the trumpet, would be impossible except by the _substitution_
of a new material; by replacing the wood with metal we may adhere
to the old Type, but we have created a new Class. (Attention is
requested to this point, because the current views respecting the
transmutation of tissues, which seem to lend a decisive support to the
hypothesis of the transmutation of species are very commonly vitiated
by the confusion of transformation with substitution. No anatomical
element is _transformed_ into another specifically different--an
epithelial-cell into a nerve-cell, for instance--but one anatomical
element is frequently _substituted_ for another.) To convert the Pipe
or the Trumpet into a Violin or a Drum would be impossible. We can
follow the modifications of a Tambourine into a Drum or Kettle-drum,
but no modifications of these will yield the Cymbals. That is to say,
the vibrating materials--wood, metal, parchment, and the combination
of wood and strings--have peculiar properties, and the instruments
formed of such materials must necessarily from the very first belong
to different groups, each subdivision of the groups being dependent on
some characteristic difference in methods of impressing the vibrations,
or in the materials. Although all musical instruments have a common
property and a common purpose, we do not regard them as transformations
of one primitive instrument; their kindred nature is a subjective
conception; the analogies are numerous and close, but we know their
origin. It is obvious that men being pleased by musical tones, have
been led by their delight to construct instruments whenever they have
discovered substances capable of musical vibrations, or methods of
impressing such vibrations. By substituting the bow for the plectrum or
the fingers, they may have changed the Lyre into the Violin, Viola,
Violoncello, and Bass. (It seems historically probable that the real
origin of the Violin class was an instrument with one string played on
by a bow.) By grouping together Pipes of various sizes they got the
Panpipes; by substituting metal and enlarging the blowing apparatus
they got the Organ. By beating on stretched parchment with the finger,
they got the Tambourine and Tom-Tom; by doubling this and using a stick
they got the Drum. By beating metal with metal they got the Cymbals; by
beating wood they got the Castanets.
137. The application of this illustration is plain. Just as a
wind-instrument is incapable of becoming a stringed instrument, so
a Mollusc, with all its muscles unstriped, and its nervous system
unsymmetrical, is incapable of becoming a Crustacean, with all its
muscles striped and its nervous system symmetrical. Indeed there
are probably few biologists of the present day who imagine the
transmutation of one kind into the other to be possible; but many
biologists assume that both may have been evolved from a common root.
The point is beyond proof; yet I think there is a greater probability
in the assumption that both were evolved from different roots. At any
rate, one thing is certain; a divergence could only have been effected
by a series of _substitutions_; and the question when and how these
substitutions took place is unanswerable: one school believes them to
have been creative fiats, the other school believes them to have been
transmutations.
138. When we see an annelid and a vertebrate resembling each other in
some special point which is not common either to their classes or to
any intermediate classes--as when we see the wood-louse (_Oniscus_)
and the hedgehog defend themselves in the same strange way by rolling
up into a ball--we cannot interpret this as a trace of distant
kinship. When we see a breed of pigeons and a breed of canaries
turning somersaults, and one of the Bear family (_Ratel_) given to the
same singular habit, we can hardly suppose that this is in each case
inherited from a common progenitor. When we see one savage race tipping
arrows with iron, and another, ignorant of iron, using poison, there is
a community of object effected by diversity of means; but the analogy
does not necessarily imply any closer connection between the two races
than the fact that men with similar faculties and similar wants find
out similar methods of supplying their wants. Even those who admit that
the human race is one family, and that the various peoples carried with
them a common fund of knowledge when they separated from the parent
stock, may still point to a variety of new inventions and new social
developments which occurred quite independently of each other, yet are
strikingly alike. Their resemblance will be due to resemblance in the
conditions. The existence, for example, of a religious worship, or a
social institution, in two nations widely separated both in time and
space, and under great historical diversities, is no absolute proof
that these two nations are from the same stock, and that the ideas have
the same parentage. It may be so; it may be otherwise. It may be an
analogy no more implying kinship than the fact of ants making slaves
of other ants (and these the black ants!) implies a kinship with men.
Given an organization which in the two nations is alike, and a history
which is in certain characteristics analogous, there must inevitably
result religious and social institutions having a corresponding
resemblance. I do not wish to imply that the researches of philologists
and ethnologists are misdirected, or that their conclusions
respecting the kinship of mankind are to be rejected; I only urge the
consideration that perhaps too much stress is laid on community of
blood, and not enough on community of conditions.
RECAPITULATION.
139. The various lines of argument may here be recapitulated. The
organic world presents a spectacle of endless diversity, accompanied by
a pervading uniformity. The general resemblances in forms and functions
are more or less masked by particular differences. The resemblances, it
is said, may be all due to kinship, all the living individuals having
descended from a primordial cell; and at each stage of the descent the
adaptations to new conditions may have issued in deviations from the
ancestral form, while the process of Natural Selection giving stability
to those variations which best fitted the organism in the struggle of
existence, has made greater and greater gaps, and produced more marked
diversities among the descendants. This is the Darwinian Theory: “On my
theory unity of Type is explained by unity of Descent.”
140. By the general consent of biologists, this theory is held to
explain many if not all the observed facts. It is a very luminous
suggestion; but it requires an enlargement so as to include Organic
Affinity; and when once this fundamental principle is admitted, it
brings with it very serious doubts as to the theory of Descent.
We are then entitled to assume that many of the most striking
resemblances, instead of being due to kinship, are due simply to the
general principle that similar causes must have similar effects, and
that organic substances having a very close resemblance, organized
substances must have similar stages of evolution under similar
conditions; and thus organs will necessarily take on very similar forms
in very different organisms (for example, the eye of the cephalopod
and the eye of the vertebrate), and organisms having widely different
parentage may closely resemble each other. If we are entitled to
assume that protoplasm appeared not in one microscopic spot alone, but
in many places and in vast quantities--and this is surely the more
justifiable assumption--then we must also admit that these germinal
starting-points were from the first, or very shortly afterwards,
differentiated by variations in their elementary composition. Now we
know that a very minute change in composition may lead to immense
differences in evolution. Thus the descendants of two slightly
different progenitors may, by continual differentiation, become very
markedly unlike; yet, because of the original resemblance of their
substances, they will reveal a pervading similarity.
While it is thus conceivable that all organisms may resemble each
other, and all differ, owing to the similarities and diversities in the
“conditions of existence” (and among those conditions that of descent
is of wide range), it is not very readily conceivable how advantage
in the external struggle could have determined the varieties of form
and function, because many differentiations give no superiority in the
struggle. As Mr. St. George Mivart urges, “Natural Selection utterly
fails to account for the conservation and development of the minute and
rudimentary beginnings, the slight and infinitesimal commencements of
structures, however useful those structures may afterwards become.”[78]
And this is undeniable on the supposition that Natural Selection is an
agency not identical with the variations of growth, but exclusively
confined to the accumulation of favorable variations.
141. In estimating the two hypotheses--First, of Descent from one
primordial germ, and the modifications _due_ to Natural Selection, or,
as I should say, _expressed_ in Selection; and Secondly, of Descent
from innumerable germs having initial differences, which differences
radiated into the marked modifications, there is this superiority to
be claimed for the first, that it is more easily handled as an aid to
research, and is therefore more decidedly useful. The laws of Organic
Affinity are at present too obscure for any successful application.
I only wish to point out that the theory of Descent is an imaginary
construction of what _may have been_ the process of species-formation,
not a transcription of the process observed. It constructs an imaginary
Type as progenitor of a long line of widely different descendants. The
annelid which is taken as the ancestor of the vertebrates is not any
annelid known either to zoölogists or geologists, but a generalized
and imaginary type. So daringly liberal is the imagination in endowing
the ancestor with whatever may be required for the descendants, that
Mr. Darwin thinks it _probable_, from what we know of the embryos
of vertebrates, that these animals “are the modified descendants
of some ancient progenitor which was furnished in its adult state
with branchiæ, a swim-bladder, four simple limbs, and a long tail,
all fitted for an organic life,” (p. 533); and Dr. Dohrn conceives
the original type to have contained within itself all that has been
subsequently evolved in the highest vertebrate, the other and less
elaborate organisms being mere degradations from this type.[79] This
use of the imagination, although not without advantages, is also not
without dangers. It may direct research, it must not be suffered to
replace research.
PROBLEM II.
THE NERVOUS MECHANISM.
“All the functions of the nervous system are as dependent upon its
structure and nature, as the accurate indication of time upon the
construction of the chronometer.”--PROCHASKA.
“Unser Wissen wird nie vollendet, ist und bleibt Stückwerk; dessen
Ergänzung das Streben und Hoffen der forschenden Denker bleiben
wird für alle Zeit.”--RADENHAUSEN, _Osiris_.
“Our nimble souls
Can spin an insubstantial universe
Suiting our mood, and call it possible,
Sooner than see one grain with eye exact,
And give strict record of it.”
GEORGE ELIOT, _The Spanish Gypsy_.
“If we compare the teachings of our books with what Nature is
constantly showing, we find there is no agreement between those two
sources of learning.”--BROWN SÉQUARD.
THE NERVOUS MECHANISM.
CHAPTER I.
SURVEY OF THE SYSTEM.
1. Our knowledge of mental processes is derived from reflection on our
personal experiences, combined with inferences from our observation
of other men and animals, under similar conditions. The processes
are complex and variable; so complex and variable, that knowledge of
their component factors can only be gained through long tentative
study, aided by fortunate circumstances which present these factors
separately, or at any rate in such marked predominance as to fix
attention. This subjective analysis of the _processes_ has to be
supplemented by, and confirmed by an objective analysis of, the
_conditions_, external and internal: the facts of Feeling have to be
traced to facts of Physiology, which will exhibit that Physical Basis
of Mind so earnestly sought by the inquirer.
Both the subjective and the objective analysis are at present in a
very imperfect state. Although there is much confident assertion and
“false persuasion of knowledge” in both regions, there is, unhappily,
little that can be seriously accepted as demonstrated. In the present
volume we shall concern ourselves almost exclusively with the objective
analysis, and do our utmost to mark what is mere inference from what
is verified observation. It is only by Observation that facts can be
_settled_; however Analogy and Inference may suggest where the truth
may lie, they are finger-posts, not goals. At the best they only tell
us what Observation _would_ reveal could the processes be submitted to
Sense.
In a loose and general way every one knows that the Nervous System is
a dominant agent in all sentient processes; although not by any means
the only agent, yet, because of its predominance, it is artificially
accepted as the only one. With the greater complexity of this system,
there is observed a corresponding increase in the variety of sentient
phenomena. The labors of anatomists have secured a tolerably exact plan
of the topographical distribution of this system; a somewhat chaotic
mass of observation and inference passes as a description of its
elementary structure. The labors of physiologists have succeeded to a
small extent in localizing certain functions in certain organs of this
system. But imperfect as our knowledge of the elementary structures is,
our knowledge of the functions is still more so. I wish I could say
otherwise, and that I could ask my readers to accept with confidence
what teachers confidently propound. The attitude of scepticism is
always repulsive; the sceptic is seldom received without disfavor,
because he throws on us the labor of investigation there where we wish
for the confidence of knowledge. Yet it is only by facing the facts
that we can hope one day to solve the great questions.
2. The nervous system has, in our artificial view of it, two divisions:
the Peripheral, which connects the organism with the external world;
and the Central, which connects each part of the organism with all
the other parts. Although the system is constituted by various
tissues--neural, connective, vascular, and elastic--it receives its
characteristic designation from nerve-fibrils, nerve-fibres, and
nerve-cells; just as the muscular system receives its designation
from contractile cells and fibres. This neural tissue assumes three
well-marked forms: 1°, _nerves_, which are bundles of fibres and
fibrils, enclosed in a membranous sheath; 2°, _ganglia_, which are
clusters of cells, fibres, and fibrils, sometimes enclosed in a sheath,
sometimes not; 3°, _centres_, which are artificial divisions of the
neural axis, serving as points of union for different organs.
In the Invertebrata the neural axis is the chain of ganglionic masses
running along the ventral side, and giving off the nerves to organs of
sense, and to the muscles. It may be seen represented in Fig. 1.
[Illustration: Fig. 1.--_Nervous system of a beetle._ The small round
masses, or _ganglia_, are seen to be connected by longitudinal fibres,
and from the ganglia issue fibres to the limbs, organs of sense, and
viscera.]
In the Vertebrata the axis is dorsal, and is called the _cerebro-spinal
axis_, including brain and spinal cord. When we look at this structure
superficially we see various nerves radiating _from_ it to skin,
glands, and muscles; but a closer examination, enlightened by knowledge
of function, shows that some of these nerves pass _into_ it from the
various surfaces and sense-organs, and are therefore called _afferent_
or _sensory_; whereas another set passes out of it to glands and
muscles, and these nerves are therefore called _efferent_ or _motory_.
There are also fibres which, passing from one part of the great centre
to another, are called _commissural_.
To this brief account of the cerebro-spinal system may be added a word
on the connected chain of ganglia and nerves known as the Sympathetic,
because it was formerly supposed to be the organ through which the
various “sympathies” were effected. It is now held to be the system
devoted to the viscera and blood-vessels; but there is still great want
of agreement among physiologists as to whether it is an independent
system, having a special structure somewhat different from that of the
cerebro-spinal, or whether it is simply a great plexus of nerves and
ganglia, only topographically distinguishable from the rest of the
nervous system. Into this point it is unnecessary for me to enter here.
Enough to say, that I entirely agree with Sigmund Mayer in adopting
the second view.[80] In no histological character, yet specified, are
the sympathetic nerves and ganglia demarcated from the others. There
are, indeed, _more_ non-medullary fibres (the gray fibres of Remak)
in the sympathetic; but the same fibres are also abundant in the
cerebro-spinal system; and the sympathetic has also its large medullary
fibres.
3. The Centres are composed of two substances: the gray and the white.
The gray substance is often called the vesicular because of its
abundant cells; but it has even more fibres than cells, and the white
substance has also a few cells.[81] The gray substance is distributed
over the surface of the brain--in the convolutions; and in various
other parts of the encephalon. It surrounds the central canal which
forms the ventricles of the brain and is continued as a very small
cavity all down the spinal cord. Besides entering into the important
and conspicuous masses known as the cerebral ganglia--(the _optic
thalami_, and _corpora striata_)--the gray substance is massed in the
_corpora quadrigemina_, _crura cerebri pons varolii_, and _medulla
oblongata_. We shall have occasion to refer to each of those parts.
Until modern times all the masses included in the skull under the
familiar term Brain (or the technical term Encephalon) were regarded
as the only centre, and also as the origin of all the nerves. Nor has
this notion even yet entirely disappeared, although the spinal cord
is known not to be a large nerve trunk, but a centre or connected
chain of centres, structurally and functionally similar to the cranial
centres. The shadow of the ancient error still obscures interpretation
of the part this spinal cord plays in the sentient mechanism; and thus
although the cord is universally admitted to be a centre for “sensitive
impressions,” it is usually excluded from Sensation. This widespread
and misleading notion will be critically examined in a future problem.
4. Beginning our survey of the cerebro-spinal axis with the Spinal
Cord, we observe it to consist: 1°, of _central gray substance_
surrounding the scarcely visible canal, which is all that remains of
the primitive groove in the germinal membrane (§ 9); 2°, irregular
gray masses, called the _anterior and posterior horns_,[82] connected
with the anterior and posterior _roots_ of the spinal nerves; and 3°,
strands of white fibres enclosing this central substance, and called
the _anterior lateral and posterior columns_.
Like the Cerebrum, it is a double organ formed by two symmetrical
halves, as the cerebrum is of two hemispheres. Each half innervates
the corresponding half of the body. The cord is unlike the cerebrum
in external form, though very like it in internal structure. The gray
structure is mainly external in the cerebrum, and is internal in the
cord.
From the anterior side of the cord (that which in animals is the under
side) the motor nerves issue; from the posterior (in animals the
upper) side, issue the sensory nerves. On each of the sensory nerves
there is a ganglion. The _roots_ of each nerve, formed of several
rootlets issuing from the anterior and posterior columns, subsequently
unite together, and proceed in a single sheath to muscles and skin,
separating again, however, before they reach muscles and skin. Fig. 2
represents this arrangement.
[Illustration: Fig. 2.--_A portion of the spinal cord with its nerves_
(after Bernard). The left-hand figure shows the anterior side; the
right-hand the posterior. A the anterior, and P, the posterior root,
they meet at _g_, the ganglion; _c_ and _d_ are filaments connecting
two posterior roots.]
5. There are thirty-one pairs (sometimes thirty-two) of such
nerves--namely, eight cervical, twelve thoracic, five lumbar, five
sacral, and one (or two) coccygeal. Figs. 3 to 6 represent transverse
sections, which display the entrance of the roots of the nerves into
the anterior and posterior horns.
6. Similar masses of gray substance in the _Medulla Oblongata_ (which
is the name given to the cord when it passes into the skull)[83] are
supposed to be the origins of some other nerves (the cranial).
[Illustration: Fig. 3.--_Transverse section of one half of the
spinal cord in the lumbar region_ (after Kölliker). _a_, anterior
root entering the anterior gray horns, _m_ and _l_, where cells are
clustered; _c_, central canal; _d_ and _e_, the anterior and posterior
commissures uniting the two halves of the cord; _b_, posterior root
entering the posterior gray horn.]
[Illustration: Fig. 4.--_Transverse section of both halves of the cord,
cervical region._ _a_, Fissure separating the anterior columns; _b_,
fissure of the posterior.]
[Illustration: Fig. 5.--_Transverse section of the cord in the dorsal
region._]
[Illustration: Fig. 6.--_Transverse section in the lumbar region._]
Although the Medulla Spinalis is unquestionably continued as the
Medulla Oblongata, the arrangement of its tissues here becomes
gradually changed, and so complicated that it baffles the scalpel.
Anatomists are, however, agreed on the one point of fundamental
importance to us here--namely, that there is only a rearrangement, not
a new tissue. Accepting the artificial division into two organs, we may
say that their functions are different, inasmuch as they are different
in their anatomical connections--they innervate different parts; but as
nerve-centres they have one and the same property.
On its posterior surface the Medulla Oblongata opens as the _fourth
ventricle_. It is then no longer a closed canal, but an expansion of
the spinal canal, which is covered by the Cerebellum. On its anterior
surface projects the _pons varolii_. Figs. 7 and 8 represent these.
[Illustration:
Fig. 7.--_Back, or upper view of the Medulla Oblongata as it
continues the Med. Spinalis._ 1, Section of the thalami; 2, corpora
quadrigemina (the two lower bodies are imperfectly represented in
the engraving); 3, section of the crura cerebelli; 4, the fourth
ventricle; 5, the restiform bodies; 6, the calamus scriptorius.
]
[Illustration:
Fig. 8.--_Front, or under view of the Med. Oblong._ 1, Optic nerves
cut off at the chiasma; 2, crura cerebri; 3, pons varolii; 4,
olivary bodies; 5, anterior pyramids; 6, spinal columns.
]
While thus on the one hand continuing the Medulla Spinalis, the
Medulla Oblongata is seen on the other hand to be continuous with the
Brain--its white columns passing upwards in the _crura cerebri_, its
cavity repeated in the other ventricles. Above it lie the ganglionic
masses, the _corpora quadrigemina_, _optic thalami_, and _corpora
striata_. Crowning these are the big and little brains, Cerebrum and
Cerebellum. Figs. 9 and 10 represent this relation of Medulla Spinalis,
Medulla Oblongata, and Brain. Fig. 11 is a purely artificial diagram
which will give the reader some idea of the disposition of the white
and gray substances.
[Illustration:
Fig. 9.--_Human Brain in Profile._ 1, Cerebrum; 2, cerebellum; 3,
pons varolii and medulla oblongata.
]
[Illustration:
Fig. 10.--_One half of the Brain in Profile, from the inside._
1, Convolutions of the cerebrum; 2, corpus callosum or great
commissure uniting the two hemispheres; 3, arbor vitæ or branching
arrangement of gray and white matter in the cerebellum; 4, pons
varolii and medulla.
]
[Illustration:
Fig. 11.--_Diagram of a vertical section of the Brain_ (after
Dalton). 1, Olfactory ganglion; 2, cerebral hemisphere; 3, corpus
striatum; 4, thalamus; 5, corpora quadrigemina; 6, cerebellum; 7,
ganglion of the pons varolii; 8, olivary body.
]
7. In man the Cerebrum is to the Cerebellum as 9 to 1. In the lower
vertebrates the preponderance is still greater. The cerebrum is in our
artificial systems commonly divided into three lobes. The frontal lobe
is that portion which lies in front of the deep fissure named after
Rolando; between that fissure and the “internal perpendicular fissure”
lies the parietal lobe; behind this we have the occipital lobe; and,
below the fissure of Sylvius, the tempero-sphenoidal lobe. Each lobe is
again subdivided according to its convolutions.
The disposition of the fibres in the brain is far too complex to be
accurately followed. All that we can say is, that there are strands
which connect one convolution with another, strands which connect
one hemisphere with another, strands which connect cerebrum with
cerebellum, and strands which connect the cerebrum with the lower
ganglia. It is important to conceive this distinctly; for we shall
hereafter see that the function of the Brain (by brain is here meant
both Cerebrum and Cerebellum) is not that of _innervation_, but of
_incitation and regulation_. To speak metaphorically, it is the
coachman who holds in his hands the reins, and guides the team. One
cardinal fact should arrest attention, namely, that not a single nerve
in the body has its origin or centre of innervation in the cerebrum and
cerebellum. The olfactory and optic nerves do indeed _seem_ to issue
from the cerebrum; and are commonly described as cerebral nerves. But
the facts of Development, minute Anatomy, and Experiment prove this to
be inexact. Although I shall continue to speak of the olfactory and
optic nerves in accordance with universal usage, not wishing to burden
the reader with unnecessary innovations, I must at the outset express
my opinion that these nerves cannot be brought under the same general
type as the other sensory nerves. Embryology and Anatomy suggest that
they have no more claim to the title than the _crura cerebri_. Of this
hereafter. Setting these aside, no one now refuses to acknowledge
that Cerebrum and Cerebellum, although centres of Incitation and
Association, are not the centres of direct Innervation: the organic
mechanism in all its _physiological_ processes will act independently
of them (so far as such artificial distinctions are admissible at all).
This does not throw a doubt on their _physiological_ functions, nor on
their participation in the normal execution of physiological processes.
8. From this rapid survey two important points may be selected for
special attention. First, the continuity of the neural axis throughout;
secondly, the fundamental similarity of its _structure_, underlying
great variations in its form and connections. This, which is the
anatomical expression of the Unity of the nervous system, will become
more evident after we have expounded what Embryology and Microscopic
Anatomy teach. We may therefore digress here awhile to consider
THE EARLY FORMS OF NERVE CENTRES.
9. In the outermost layer of the germinal membrane of the embryo a
groove appears, which deepens as its sides grow upwards, and finally
close over and form a canal. This canal is composed of cells all alike.
Its foremost extremity soon bulges into three well-marked enlargements,
which are then called the _primitive cerebral vesicles_. The cavities
of these vesicles are continuous. Except in position and size, there
are no discernible differences in these vesicles, which are known as
the Fore-brain, Middle-brain, and Hind-brain.
10. The _Fore-brain_ soon buds off from each side a small vesicle. This
is the optic vesicle, the first rudiment of what subsequently becomes
optic nerve and retina. At this period it is simply a vesicle with
a hollow stem, the cavity being continuous with the cavity of the
cerebral vesicle, and the walls continuous with the cerebral wall.
It thus appears that the retina and optic “nerve” are primitive
portions of the brain--a detached segment of the general centre,
identical in structure with the cerebral vesicle, and not unlike in
form. A cup-like depression quickly forms the optic vesicle into an
inner and an outer fold. The inner or concave fold becomes the retina,
and the outer or convex fold (that nearest to the brain) becomes its
choroid membrane. On the fourth day of incubation the retina of the
chick is composed of spindle-shaped cells, all alike. On the seventh
day there is a differentiation into layers, one of which on the eighth
day is granular; on the tenth two are granular; and on the thirteenth
ganglionic cells appear. Some of the cells have elongated into radial
fibres (known as Müller’s fibres); and with the appearance of rods and
cones the normal retinal elements are complete.
11. The researches of Foster and Balfour[84] confirm the statement that
all the different parts of the retina (whether nervous or connective)
are derived from one and the same layer of embryonic cells, which
originally formed a portion of the first cerebral vesicle.
12. Meanwhile the hollow stem of this optic vesicle begins to develop
fibres amidst the nuclei of its walls. The “optic nerve” arises: it
is still hollow; and in birds remains so through life. The fibres as
they are developed _grow forwards towards the retina_, and spread over
its internal surface. _They also grow forwards towards the brain_,
and spread over its substance; but it is _not_, as might be supposed,
and is generally believed, with the cerebral hemispheres (or that
portion of the Fore-brain from which these are derived), but with the
Middle-brain (which becomes the _corpora quadrigemina_), that the optic
fibres are in connection.[85]
13. This will be understood when the further development is traced.
The Fore-brain, after budding off the optic vesicles, buds off two
larger vesicles--the future cerebral hemispheres. This is noticeable
on the second day of incubation, and by the third day each vesicle is
as large as the whole of the original Fore-brain. Their development is
essentially like that of the optic vesicles; both as to the cellular
and the fibrous elements.
The _convolutions_, _corpus callosum_, _nucleus lentiformis_,
and _corpora striata_ are then indicated. Meanwhile, that which
originally was the Fore-brain has lapsed into the secondary rank as
Intermediate-brain (_Zwischenhirn_), and becomes the parts surrounding
the third ventricle, namely, the _thalami_, _corpora candicantia_,
_infundibulum_, and what is called the “posterior perforated substance.”
14. The _Middle-brain_, or Second Vesicle, develops the _corpora
quadrigemina_ from the roof of its cavity, and the _crura cerebri_ from
its floor.
The _Hind-brain_, or Third Vesicle, divides into two, like the First
Vesicle; it buds off the hemispheres of the cerebellum; its cavity
forms the fourth ventricle; its walls the _medulla oblongata_.
15. It thus appears that the primitive membrane forms into a canal,
which enlarges at one part into three vesicles, and from these are
developed the encephalic structures. The continuity of the walls
and cavities of these vesicles is never obliterated throughout the
subsequent changes. It is also traceable throughout the medulla
spinalis. And microscopic investigation reveals that underneath all the
morphological changes the walls of the whole cerebro-spinal axis are
composed of similar elements on a similar plan.[86]
16. Two conclusions directly follow from this exposition:--first, that
_since the structure of the great axis is everywhere similar, the
properties must be similar_; secondly, that _since there is structural
continuity, no one part can be called into activity without at the same
time more or less exciting that of all the rest_.
THE PERIPHERAL SYSTEM.
17. Following the analytical division, we now come to the Peripheral
System of nerves and ganglia. The separation, I must often repeat,
is purely artificial; but the artifice has conveniences. We separate
in the same way the heart from veins and arteries, and the capillary
circulation from the arterial.
Each nerve has its direct connection with a particular centre, and
indirectly with the whole system. It has its circumscribed territory,
and individual office. Except in a few cases of anastomosis, the action
of one nerve does not involve that of another: only one muscle or one
group of muscles is moved, without exciting motion in a neighbor. It is
through the centres that these individual territories are united; and
a wave of excitation always passes throughout the central substance.
Thus the centres are not simply organs of association, consequently of
regulation, but are the nexus whereby the diversity of the actions is
integrated into the unity of consensus.
18. Nothing further need at present be stated respecting the nerves;
but it is needful to give precision to the ideas of
GANGLIA AND CENTRES,
usually spoken of as if they were convertible terms. That this is
inexact may be readily shown, and that it is misleading appears in its
causing physiologists to credit every ganglion, wherever found, with
central functions; and, by an almost inevitable extension of the error,
has led to the assignment of central functions to a single ganglionic
cell! This is but part of that “superstition of the cell” against
which I shall have to protest. I will not here raise the doubt which
presses from various sides respecting the central functions of the
ganglia in the heart and intestines, because the reader perhaps shares
the general opinion on that point; but let me simply ask what central
function can possibly be assigned to the ganglia on each of the spinal
sensory nerves? above all to those grouped and scattered ganglionic
cells which are found at the peripheral termination of some nerves, and
in the very trunks of others? There may, indeed, be imagined a central
function for the ganglia in the mesentery, and even in the choroid coat
of the retina, on the hypothesis (quite gratuitous, I think) of their
regulating the circulation; but even this explanation cannot be adopted
with respect to the ganglionic cells which appear in the course of the
nerve.[87]
The meaning of a physiological centre is, that it is a point _to_ which
stimulations proceed, and _from_ which they are reflected. The meaning
of a ganglion is, that it is a group of nerve cells dispersed among, or
in continuation with, nerve fibres: it may be a centre of reflection,
or it may not; and in the latter case its physiological office is at
present undetermined. A ganglion is no more a centre in virtue of its
cell-group than a muscle is a limb. All function depends on connection,
and central function demands a connection of afferent and efferent
parts.
19. The ganglia found in the ventral cord of the Invertebrate (see
Fig. 1) are centres, each of which has considerable independence,
each regulating a single segment of the body, or a group of similar
segments. As the scale of animal complexity ascends, these separated
centres tend more and more to coalesce, and with this coalescence
comes an increasing _combination_ of movements.[88] Observe the
caterpillar slowly crawling over a leaf; each segment of its body moves
in succession; but when this caterpillar becomes a butterfly the body
moves rapidly, and all at once. Open the caterpillar, and you find its
nervous centres are thirteen separate ganglia, each presiding over a
distinct part of the body, and each capable of independent action.
Open the butterfly, and you find the thirteen ganglia greatly changed:
the second and third are fused into one; the fourth, fifth, and sixth
into another; the eleventh and twelfth into another; the only trace of
the original separation is in a slight constriction of the surface. The
movements of the caterpillar were few, simple, slow, and those of the
butterfly are many, varied, and rapid.
20. In the Vertebrates the coalescence of ganglia is such that the
spinal axis is one great centre. We do indeed anatomically and
physiologically subdivide it into several centres, because several
portions directly innervate separate organs; but its importance lies in
the intimate blending of all parts, so that _fluctuating combinations_
of its elements may arise, and varied movements result. Each centre
combines various muscles; the axis is a combination of centres. The
brainless frog, for instance, has still the spinal cord, and therefore
the power not only of moving either of his limbs, but also of combining
their separate movements: if grasped, he struggles and escapes; if
pricked, he hops away. But these actions, although complex, are much
less complex and varied than the actions of the normal frog.
There is not only a coalescence of ganglia, but a greater and greater
concentration of the substance in the upper portions of the axis. In
the inferior vertebrates, and in the mammalian embryo, the spinal
cord occupies the whole length of the vertebral canal from the head
to the tip of the tail; and here the centres of reflexion correspond
with the several segments. But as the cranial mass develops there is a
withdrawal of neural substance from the lower parts, and the centres of
reflexion are then some way removed from the segments they innervate.
In the animal development there is even a greater and greater
predominance of the upper portions, so that the brain and medulla
oblongata are of infinitely more importance than the spinal cord.
21. Besides the central group of elements which belong to fixed and
definite actions, we must conceive these elements capable of variable
combinations, like the pieces of colored glass in a kaleidoscope, which
fall into new groups, each group having its definite though temporary
form. The elements constitute really a continuous network of variable
forms. It is to such combinations, and not to fixed circumscribed
ganglia, that we must refer the subordinate centres of the axis. We
speak of a centre for Respiration, a centre for Laughing, a centre for
Crying, a centre for Coughing, and so on, with as much propriety as
we speak of a centre for Swallowing or for Walking. Not that in these
cases there is a circumscribed mass of central substance set apart for
the innervation of the several muscles employed in these actions, and
for no other purpose. Each action demands a definite group of neural
elements, as each geometric form in the kaleidoscope demands a definite
group of pieces of glass; but these same pieces of glass will readily
enter into other combinations; and in like manner the muscles active
in Respiration are also active in Laughing, Coughing, etc., though
differently innervated and co-ordinated.
22. The physiological rank of a centre is therefore the expression of
its power of fluctuating combination. The medulla oblongata is higher
than the medulla spinalis, because of its more varied combinations;
the cerebrum is higher than all, because it has no fixed and limited
combinations. It is the centre of centres, and as such the supreme
organ.