_perpetuum mobile_. There is no real rest anywhere; it is always
only apparent or relative. Heat itself, which constantly changes, is
merely motion. In the eternal play of cosmic bodies countless suns and
planets rush hither and thither in infinite space. In every chemical
composition and decomposition the atoms, or smallest particles of
matter, are in motion, and so are the molecules they compose. The
incessant metabolism of the living substance is associated with a
constant movement of its particles, with the building up and decay of
plasma-molecules. But here we must disregard all these elementary kinds
of movement, and be content with a brief consideration of those forms
of motion which are peculiar to organic life, and a comparison of them
with the corresponding motions of inorganic bodies.
The science of motion, or mechanics, is now taken in very different
senses: (1) in the widest sense as a philosophy of life [generally
called mechanism or mechanicism in England], equivalent to either
monism or materialism; (2) in the stricter sense as the physical
science of motion, or of the laws of equilibrium and movement in
the whole of nature (organic and inorganic); (3) in the narrowest
sense as part of physics, or dynamics, the science of moving forces
(in opposition to statics, the science of equilibrium); (4) in the
purely mathematical sense as a part of geometry, for the mathematical
definition of magnitudes of movement; and (5) in the biological sense
as phoronomy, the science of the movements of organisms in space.
However, these definitions are not yet universally adopted, and
there is a good deal of confusion. It would be best to follow the
lead of Johannes Müller, as we are going to do here, and restrict
the name phoronomy to the science of the vital movements which are
peculiar to organisms, in contrast to kinematics, the exact science
of the inorganic movements of all bodies. The real material object
of phoronomy is the plasm, the living matter that forms the material
substratum of all active vital movements.
On our monistic principles the inner nature of organic life consists in
a chemical process, and this is determined by continuous movements of
the plasma-molecules and their constituent atoms. As we have already
considered this metabolism in the tenth chapter, we need do no more
here than point out that both the general phenomena of molecular
plasma-movement and their special direction in the various species of
plants and animals can be reduced in principle to chemical laws, and
are subject to the same laws of mechanics as all chemical processes
in organic and inorganic bodies. In this we emphasize our opposition
to vitalism, which sees in the _direction_ of plasma-movement the
supernatural influence of a mystical vital force or of some ghostly
"dominant" (Reinke). We agree with Ostwald, who also reduces these
complex movements to the play of energy in the plasm--that is to say,
in the last instance to modifications of chemical energy. In regard to
the visible movements of the living things which concern us at present,
we must first distinguish passive and active, and subdivide the latter
into reflex and autonomous.
Many movements of the living organism which the inexpert are inclined
to attribute to life itself are purely passive; they are due either to
external causes which do not proceed from the living plasm, or to the
physical composition of the organic but no longer living substance.
Purely passive movements, which play an important part in bionomy and
chorology, comprise such as the flow of water and the rush of the wind;
they cause considerable changes of locality and "passive" migrations
of animals and plants. Purely physical, again, is what is known as the
Brownian molecular movement which we observe with a powerful microscope
in the plasm of both dead and living cells. When very fine granules
(for instance, of ground charcoal) are equally distributed in a liquid
of a certain consistency, they are found to be in a constant shaking or
dancing movement. This movement of the solid particles is passive, and
is due to the shocks of the invisible molecules of the fluid which are
continually impinging upon each other. In the rhizopods--the remarkable
protozoa whose unicellular organism sheds so much light on the obscure
wonders of life--we notice a curious streaming of the granules in
the living plasm. Within the cytoplasm of the amœbæ particles
travel up and down in all directions. On the long thin plasma-threads
or pseudopodia which stream out from the unicellular body of the
radiolaria and thalamophora, thousands of fine particles move about,
like promenaders in a street. This movement does not come from the
passive granules, but from the active invisible molecules of the
plasm, which are always changing their relative positions. Thus also
the movements of the blood-cells which we can see with the microscope
in the circulation of a young transparent fish, or in the tail of a
frog-larva, are not due to the action of the blood-cells themselves,
but to the flow of the blood caused by the beat of the heart.
An important factor in the life of many organisms, especially the
higher plants, is the physical phenomenon called _imbibition_; it
consists in the penetration of water between the molecules of solid
bodies (drawn to them by molecular attraction), and the consequent
displacement of the molecules by the fluid. In this way the volume of
the solid body is increased, and movements are produced which may have
the appearance of vital processes. The energy of these imbibitional
bodies is notoriously very powerful; we can, for instance, split large
blocks of stone by the insertion of a piece of wood dipped in water. As
the cellulose membrane of plant-cells has this property of imbibition
in a high degree (either in the living or the dead cell), the movements
it causes are of great physiological importance. This is especially
the case when the imbibition of the cell wall is one-sided, and causes
a bending of the cell. In consequence of the unequal strain in the
drying of many fruits, they split open and project their seeds to some
distance (as do the poppy, snap-dragon, etc.). The moss-capsules also
empty their spores as a result of imbibition-curving (in the teeth
of the openings of the spore-cases). The hygroscopic points of the
heron-bill (_erodium_) curl up in the dry state and stretch out when
moist; hence they are used as hygrometers in the construction of
meteorological huts. The so-called "resurrection plants" (_anastatica_,
the rose of Jericho, and _selaginella lepidophylla_), which close up
like a fist when dry, spread their leaves out flat when moistened (the
leaves imbibing strongly on the inner side). There is no more real
case of "resuscitation" (as many believe) in these cases than in the
mythological resurrection of the body. However, these phenomena of
imbibition are not active vital processes; they are independent of the
living plasm, and due solely to the physical constitution of the dead
cell-membranes.
In contrast with these passive movements of organisms, we have
the active movements which proceed from the living plasm. In the
ultimate analysis, it is true, these may be reduced to the action of
physical laws just as well as the passive movements. But the causes
of them are not so clear and obvious; they are connected with the
complicated chemical molecular processes of the living plasm, of the
physical regularity of which we are now fully convinced, though their
complicated mechanism is not yet understood. We may divide into two
groups the many different movements, which are called vital in this
stricter sense, and were formerly regarded as evidences of the presence
of a mystic vital force, according as the stimulus--the sensation of
which is caused by the movement--is directly perceptible or not. In
the first case, we have stimulated (or reflex or paratonic) movements,
and in the second voluntary (autonomous or spontaneous) movements. As
the will appears to be free in the latter, they have been left out of
consideration by many physiologists, and handed over to the treatment
of the metaphysical psychologist. On our monistic principles this is a
grave error; nor is it improved when "psychonomism" appeals to a false
theory of knowledge. On the contrary, the conscious will (and conscious
sensation) is itself a physical and chemical process like unconscious
and involuntary movement (and unconscious feeling). They are both
equally subject to the law of substance. However, only the external
stimuli which cause reflex movements are known to us to any great
extent and experimentally recognizable; the internal stimuli, which
affect the will, are mostly unknown, and are not directly accessible
to investigation. They are determined by the complicated structure of
the psychoplasm, which has been gradually acquired by phylogenetic
processes in the course of millions of years.
The great problem of the will and its freedom--the seventh and last
of Dubois-Reymond's world-riddles--has been dealt with fully in the
_Riddle_ (chapter vii.). But as we still meet with the most glaring
contradictions and confusion in regard to this difficult psychological
question, I must touch upon it briefly once more. In the first place, I
would remind the reader that it is best to restrict the name "will" to
the purposive and conscious movements in the central nervous system of
man and the higher animals, and to give the name of impulses (tropisms)
to the corresponding unconscious processes in the psychoplasm of the
lower animals, as well as of the plants and protists. For it is only
the complicated mechanism of the advanced brain structure in the higher
animals, in conjunction with the differentiated sense-organs on the one
side and the muscles on the other, that accomplishes the purposive and
deliberate actions which we are accustomed to call acts of will.
But the distinction between voluntary (autonomous) and involuntary
(reflex) movements is as difficult to carry out in practice as it is
clear in theory. We can easily see that the two forms of movement
pass into each other without any sharp boundary (like conscious and
unconscious sensation). The same action, which seems at first a
conscious act of the will (for instance, in walking, speaking, etc.),
may be repeated the next moment as an unconscious reflex action. Again,
there are many important mixed or instinctive movements, the impulse to
which comes partly from internal and partly from external stimuli. To
this class belong especially the movements of growth.
Every natural body that grows increases its extent, fills a larger
part of space, and so causes certain movements of its particles; this
is equally true of inorganic crystals and the living organism. But
there are important differences between the growth in the two cases.
In the first place, crystals grow by the external apposition of fresh
matter, while cells grow by the intussusception of fresh particles
within the plasm (_cf._ chapter x.). In the second case, in growth,
which determines the whole shape of the organism, two important factors
always co-operate, the inner stimulus, which depends on the specific
chemical constitution of the species, and is transmitted by heredity,
and the external stimulus which is due to the direct action of light,
heat, gravity, and other physical conditions of the environment, and is
determined by adaptation (phototaxis, thermotaxis, geotropism, etc.).
A peculiar property of many vital movements (but by no means all)
is the definite direction they exhibit; these are generally called
purposive movements. For the teleologist they afford one of the chief
and most welcome proofs of the dualistic theory of the older and the
modern vitalism. Baer, especially, has laid stress on the purposiveness
of all vital movement. It has been given a more precise expression
recently by Reinke. His "dominants" are "intelligent directive
forces," essentially different from all forms of energy or natural
forces, and not subject to the law of substance. These metaphysical
"vital spirits" are much the same as the immortal soul of dualistic
psychology or the divine emanations of ancient theosophy. They are
supposed not only to regulate the special development and construction
of every species of animal and plant, and direct it to a predetermined
end, but also to control all the various movements of the organism
and its organs down to the cells. These "hyperenergetic forces" are
equivalent to the "organizing principle" and the "unconscious will"
of Edward Hartmann, the "arranging and controlling protoplasmic
forces" of Hanstein and others. All these metaphysical, supernatural,
and teleological ideas, like the older mystic notion of a special
vital force, rest on a perversion of judgment by the apparent freedom
of will and purposiveness of organization in the higher organisms.
These thinkers overlook the fact that this purposiveness can be
traced phylogenetically to simple physical movements in the lower
organisms. Moreover, they overlook or deny the definite direction of
inorganic forms of energy, though this is just as clear in the origin
of a crystal as in the composition of the whole world-structure, in
the direction of the mind as in the orbit of a planet. Hence it is
important to bear in mind always these two forms of mechanical energy,
and emphasize their identity with the direction of vital movement.
The force of gravitation which is at work in crystal-formation in
the simple chemical body exhibits just as definite a direction as
that which appears in the plasm in cell-construction. In this and
other respects the comparison of the cell with the crystal, which was
made even by the founders of the cell-theory, Schleiden and Schwann,
in 1838, is thoroughly justified, though it is not correct in some
other aspects. When the crystal is formed in the mother-water, the
homogeneous particles of the chemical substance arrange themselves
in a perfectly definite direction and order, so that mathematical
planes of symmetry and axes arise within, and definite angles at the
surface. On the strength of this, modern crystallography distinguishes
six different systems of crystals. But, in different conditions, the
same substance may crystallize in two or even three different systems
(dimorphism and trimorphism of the crystal); thus, for instance,
carbonate of lime crystallizes as calcspar in the hexagonal, and as
arragonite in the rhombic system. If Reinke would be consistent, he
ought to postulate a "dominant" for every crystal, to control the order
and direction of the particles in its formation. He makes the curious
statement (in 1899) that direction "is not a measurable magnitude" like
energy, and so is not subject, like it, to the law of substance. We can
mathematically determine the direction of the constructive force in the
crystal just as well as in the cell.
If we comprise under the head of cosmokinesis the whole of the
movements of the heavenly bodies in space, we cannot deny that they
have a definite direction in detail, although our knowledge of this is
still very incomplete. We can calculate the distances and speeds and
movements of the planets round the sun with mathematical accuracy; and
we gather from our astronomical observations and calculations that a
similar regularity prevails in the movements of the other countless
bodies in infinite space. But we do not know either the first impulse
to these complex movements or their final goal. We can only conclude
from the great discoveries of modern physics, supported by spectrum
analysis and celestial photography, that the universal law of substance
on the one side and the law of evolution on the other control the
gigantic movements of the heavenly bodies just as they do the living
swarm of tiny organisms that have inhabited our little planet for
millions of years. Reinke ought, consistently, to admire the cosmic
intelligence of the Supreme Being in these movements of the cosmic
masses and its emanations, the "dominants," in the actual direction
of their movements, as much as he does in the plasma-flow in the tiny
organism.
The manifold gradation of vital movement which we find everywhere in
the higher organisms is not without expression even in the protist
realm. In this respect the chromacea, the simplest forms of vegetal
monera, and the bacteria, which we regard as corresponding animal
forms, developed from the former by metasitism, are of great interest.
As microscopic scrutiny fails to detect any purposive organization in
these unnucleated cells, and it is impossible to discover different
organs in their homogeneous plasma-body, we have to look upon their
movements as direct effects of their chemical molecular structure. But
the same must be said also of a number of nucleated cells, both among
the protophyta and the protozoa; only in this case the structure is
less simple, in so far as both the nucleus itself and the surrounding
cell-body exhibit, in indirect division, complicated movements in the
plasm (caryokinesis). Apart from these, however, there is nothing to
be seen in many unicellular beings (_e.g._, paulotomea, or calcocytea)
that we need call "vital movement." On the border between the organic
and inorganic worlds we have, as regards movement, the simplest forms
of the chromacea, chroococcacea. We can see no vital movement in
these structureless particles of plasm except slight changes of form,
which occur when they multiply by cleavage. The internal molecular
movements of the living matter, which effect their simple plasmodomous
metabolism and growth, lie beyond our vision. The reproduction itself,
in its simplest form of self-cleavage, seems to be merely a redundant
growth, exceeding the limit of individual size for the homogeneous
plasma-globule (_cf._ chapters ix. and x.).
The great majority of the protists have the appearance of real,
nucleated cells. Hence we have to distinguish two different forms
of movement in the unicellular organism--the inner movement in the
caryoplasm of the nucleus and the outer in the cytoplasm of the
cell-body; the two enter into close mutual relations during the
remarkable process of partial resolution of the nucleus (caryolysis).
In this modification and partial dissolution of their constituents we
observe, during indirect cell-division, certain complicated movements
(the significance of which is as yet entirely unknown), that are
accomplished by both the granules of chromatin and the threads of
achromin, and which are comprised under the head of nuclear movements
(caryokinesis). It has lately been attempted to explain them on purely
physical principles. The same may be said of the internal flow of the
plasm which we find in the plasmodia of the amœbæ and mycetozoa, and
in the endoplasm of many of the protophyta and protozoa.
The slow displacement of the molecules of plasm which is at the
bottom of these plasma-movements also causes a variety of external
changes of form in simple naked cells. Variable processes like folds
or fingers (the "fold-feet," _lobopodia_) appear on their surface. As
they are best observed in the common amœbæ (naked nucleated cells
of the simplest kind), they are called amœboid movements. With
these is connected the variable movement of the larger rhizopods, the
radiolaria and thalamophora, in which hundreds of fine threads radiate
from the surface of the naked plasma-body. A number of recent experts
on the rhizopods, such as Bütschli, Richard Hertwig, Rhumbler, and
others, have attempted to trace to purely physical causes this varying
formation of pseudopodia, and their branching and net-like structure
(without definite direction).
It is more difficult to do this in the case of the most highly
differentiated of the protozoa, the infusoria. With these the free
movement of the unicellular protozoon is farther advanced through
the formation of permanent hairlike processes (long single lashes in
the flagellata, and a number of short lashes in the ciliata) on the
cell-surface and the movement of these by contraction and expansion,
like the limbs, tentacles, and bones of the higher animals. The
apparent spontaneity and various modulation in the ever-changing
movements of these cell-feet is, in many of the infusoria, so like the
autonomous voluntary movements in the metazoa that several experts on
the infusoria have been moved on this account to ascribe individual
(and even conscious) souls to them. Hence the difference between the
various kinds of living movement is already very considerable before
we leave the kingdom of the protists. On the one hand, the lowest
monera (chromacea) join on directly to inorganic phenomena. On the
other hand, the highly differentiated infusoria (ciliata) show so
great a resemblance to the higher animals in their differentiated and
autonomous movements that they have been credited with the possession
of "free-will." There is no such thing as a sharp division.
In a large section of the higher protozoa differentiated organs of
movement are developed, which may be compared to the muscles of the
metazoa. In the cytoplasm threadlike, contractile structures are
formed, and these have, like the muscular fibres of the metazoa, the
power to contract and expand again in definite directions. These
myophæna or myonema form, in many of the infusoria, both ciliata
and flagellata, a special thin layer of parallel or crossed fibres
underneath the exoplasm or the hyaline skin-layer of the cell. The
metabolic body of the infusorium may be altered in various ways by the
autonomous contraction of these. Special instances of these myophæna
are the _myophrisca_ of the acantharia--contractile threads which
surround the radial needles of these radiolaria like a crown. They
are found in their outer gelatine envelope, the calymma, and by their
contraction extend it, and so lessen the specific gravity.
Many of the aquatic protophyta and protozoa have the power of
autonomous and independent locomotion, and this often has the
appearance of being voluntary. Among the simplest fresh-water
protozoa are the arcellina or thecolobosa (_difflugia_, _arcella_),
little rhizopods that are distinguished from the naked amœbæ by
the possession of a firm envelope. They usually creep about in the
slime at the bottom, but in certain circumstances rise to the surface
of the water. As Wilhelm Engelmann has shown, they accomplish this
hydrostatic movement by means of a small vesicle of carbonic acid,
which expands their unicellular body like an air-balloon; the specific
weight of the cell-body, which is of itself heavier than water, is
sufficiently lowered by this. The same method is followed by the pretty
radiolaria which live floating (as plankton) at various depths of the
sea. Their unicellular (originally globular) body is divided by a
membrane into a firm inner central capsule and a soft outer gelatine
covering. The latter, known as the calymma, is traversed by a number
of water-vesicles or vacuoles. As a result of an osmotic process,
carbonic acid may be secreted or pure water (without the salt of the
sea-water) be imbibed in these vacuoles; by this means the specific
gravity of the cell is lessened, and it rises to the surface. When
it desires to make itself heavier and sink, the vacuoles discharge
their lighter contents. These hydrostatic movements of the radiolaria
(for which the myophrisca, still more complicated structures, have
been developed in the acantharia) attain by simple means the same end
that is accomplished in the siphonophora and fishes by air-filled and
voluntarily contractile swimming-bladders.
Numbers of the unicellulars alter their position very
characteristically by secreting a thick mucus at one side of their body
and fastening this to the ground. If the secretion continues, a longish
jelly-like stalk is produced by which the cell slowly pushes itself
along, like a boat with a rowing-pole. This secretory locomotion is
found, among the protophyta, in the desmidiacea and diatomes, and in
some of the gregarinæ and rhizopods among the protozoa. The peculiar
rolling movements of the oscillaria (threadlike chains of blueish-green
unnucleated cells, closely related to the chromacea) are also effected
by the secretion of mucus. On the other hand, it is probable that the
sliding movements of many of the diatomes are due to fine processes
(vibratory hairs?) in the plasm, which proceed either out of the seams
(_raphe_) of the bivalvular silicious shells or through the fine pores
in them.
Especially important in the easy and rapid locomotion of many
unicellulars is the formation of fine hairlike processes at the surface
of the body; in the broadest sense, they are called vibratory hairs.
If only a few whiplike threads are formed, they are called _whips_
(_flagella_); if many short ones, _lashes_ (_cilia_). Flagelliform
movement is found in some of the bacteria, but especially in the
mastigophorous "whip-infusoria," in the mastigota among the protophyta,
and the flagellata among the protozoa. As a rule, we have in these
cases one or two (rarely more) long and very thin whip-shaped
processes, starting from one pole of the long axis of the oval, round,
or long cell-body. These whips (_flagella_) are set in vibratory motion
(apparently often voluntary) in various ways, and serve not only for
swimming or creeping, but also for feeling and securing food. Similar
whip-cells (_cellulæ flagellatæ_) are also found very commonly in the
body of tissue-animals, usually packed together in an extensive layer
at the inner or outer surface (ciliated epithelium). If single cells
are released from the group, they may live independently for some time,
continuing their movements and resembling free infusoria. The same may
be said of the travelling spores of many of the algæ, and of the most
remarkable of all ciliated cells--the spermia or spermatozoa of plants
and animals.
As a rule they are cone-shaped, having an oval or pear-shaped (though
often also rod-shaped) head, which tapers into a long and thin thread.
When their lively movements were first noticed in the male seminal
fluid (each drop of which contains millions of them) two hundred years
ago, they were thought to be real independent animalcules, like the
infusoria, and so obtained their name of seed-animals (spermatozoa).
It was a long time (sixty years ago) before we learned that they are
detached glandular cells, which have the function of fertilizing the
ovum. It was discovered at the same time that similar vibratory cells
are found in many of the plants (algæ, mosses, and ferns). Many of the
latter (for instance, the spermatozoids of the cycadea) have, instead
of a few long whips, a number of short lashes (_cilia_), and resemble
the more highly developed ciliated infusoria (_ciliata_).
The ciliary movement of the infusoria is held to be a more perfect form
of vibratory movement, because the many short lashes found on them are
used for different purposes, and have accordingly assumed different
forms in the division of labor. Some of the cilia are used for running
or swimming, others for grasping or touching, and so on. In social
combinations we have the ciliated cells of the ciliated epithelium of
the higher animals--for instance, in the lungs, nostrils, and oviducts
of vertebrates.
In the unicellular, non-tissue forming protists, all the vital
movements seem to be active functions of the plasm of the single
cell; but in the histona, the multicellular tissue-forming organisms,
they are the outcome of the combined movements of the many cells
which compose the tissue. Careful anatomic study and experimental
physiological scrutiny of the motor processes are, therefore, first
directed, in the case of the histona, to clearing up the nature and
activity of the special cells which compose the tissue, and then the
structure and functions of the tissue itself. When we start from this
point, and survey the manifold active motor phenomena of the histona
as a whole, we see at once an essential agreement in the phoronomy of
the two kingdoms of the metaphyta and metazoa, in the sense that at the
lower stages the chemical and physical character of the motor processes
can be clearly shown and can be traced to an interchange of energy in
the plasm of the cells that make up the tissue. In the higher stages,
however, we find striking differences, the voluntary character of many
autonomous movements being very conspicuous in the higher animals,
and thus the great problem of the freedom of the will is added to the
purely physiological questions of stimulated movement, growth-movement,
etc.
Moreover, the movements of the metazoa are much more varied and
complicated than those of the metaphyta, in consequence of the higher
differentiation of their sense-organs and the centralization of their
nervous system. The former have generally free locomotion and the
latter not. The special mechanism of the organs of movement is also
very different in the two groups. In most of the metazoa the chief
motor organs are the muscles, which have developed in the highest
degree the power of definitely directed contraction and expansion.
In most of the metaphyta, on the other hand, the chief part of the
movements depend on the strain of the living plasm, or what is called
the _turgor_ or expansibility of the plant-cells. This is effected
by the osmotic pressure of the internal cell-fluid and the elasticity
of the cellulose wall, which is thus expanded. Nevertheless, in both
cases--and in all "vital" phenomena--the real cause of the process is,
in the ultimate analysis, the chemical play of energy in the active
plasm.
The metaphyta, with few exceptions, are fixed in one spot for life, or
only mobile for a short time when they are young. In this they resemble
the lower metazoa, the sponges, polyps, corals, bryozoa, etc. They have
not free locomotion. The motor phenomena which we find in them affect
only special parts or organs. They are mostly reflex or paratonic,
and due to external stimuli. Only a few of the higher plants exhibit
autonomous or spontaneous movement, the stimulating cause of which is
unknown to us, and which may be compared to the apparently voluntary
actions of the higher animals. The lateral feather-leaves of an Indian
butterfly flower (_hedysarum gyrans_) move in circles through the air,
like a pair of arms swinging, without any external cause; they complete
a circle in a couple of minutes. Variations in the intensity of light
have no effect on them. Similar spontaneous movements of the leaves
of several species of clover (_trifolium_) and sorrel (_oxalis_) are
performed only in the dark, not in the light. The terminal leaf of
the meadow-clover repeats its rotation, which describes more than one
hundred and twenty degrees of an arc, every two to four hours. The
mechanical cause of these spontaneous "variation movements" seems to
lie in variations of expansibility.
Voluntary and autonomous turgescence-movements of this kind are only
observed in a few of the higher plants, but stimulated movements that
are accomplished by the same mechanism are very common in the vegetal
world. We have, especially, the well-known "sleep," or nyktitropic
movements, of many plants. Many leaves and flowers hold themselves
vertically to the streaming rays of the sun. When darkness comes on
they contract, and the calices of the flowers close. Many flowers are
open for only a few hours a day. The mechanism of turgescence, which
effects these swelling movements, consists in the co-operation of the
osmotic pressure of the internal cell-fluid and the elasticity of the
strained cell-membrane enclosing the cytoplasm. The strain of the outer
cellulose membrane on the plasmatic primordial sac within it grows so
much on the accession of osmotically active matter that the internal
pressure is equal to several atmospheres, and the elastic strained
membrane stretches from ten to twenty percent. When water is withdrawn
again from one of these swollen or turgescent cells, the membrane
contracts; the cell becomes smaller, and the tissue looser. Other
stimuli besides light (heat, pressure, electricity) may produce these
expansional variations, and, as a consequence of it, certain reflex
movements (or paratonic variational movements). The most striking and
familiar examples are the flesh-eating fly-trap (_dionæa muscipula_)
and the sensitive plant (_mimosa pudica_); their contraction is caused
by mechanical stimuli, shaking, pressure, or the touching of the leaves.
Most of the higher animals have the power of free and voluntary
locomotion. It is, however, wanting in some of the lower classes,
which spend the greater part of their life at the bottom of the water,
like plants. Hence these were formerly held to be vegetable--thus
the sponges, polyps, and corals among the cœlenteria. A number
of classes of the cœlomaria have also adopted the stationary
life, such as the bryozoa and the spirobranchia among the vermalia,
many mussels (oysters, etc.), the actinia among the tunicates, the
sea-lilies (_crinoidea_) among the echinoderms, and even highly
organized articulate, such as the tube-worms (_tubicolæ_), among the
annelids, and the crawling crabs (_cirripedia_), among the crustacea.
All these stationary metazoa move freely in their youth, and swim about
in the water as _gastrulæ_, or in some other larva form. They have
taken only gradually to stationary habits, and have been considerably
modified, and often greatly degenerated, in consequence; for instance,
in the loss of the higher sense-organs, the bones, and even of the
whole head. Arnold Lang has shown this very clearly in his excellent
work on the influence of stationary life on animals. The study of
these retrogressive metamorphoses is very important for the theory of
progressive heredity and selection; it also shows the great value of
free locomotion for the higher sensitive and intellectual development
of the animals and man.
In many of the lower aquatic metazoa the surface of the body is covered
with vibratory epithelium--that is to say, with a layer of skin-cells
which bear either one long whip (_flagellum_) or several short lashes
(cilia). Flagellated epithelium is especially found in the cnidaria
and platodes; ciliated epithelium mostly in the vermalia and mollusca.
As the lashing motion of these hairlike processes brings a constant
stream of fresh water to the surface of the body, they first of all
effect respiration through the skin. But in many of the smaller metazoa
they also serve the purpose of locomotion, as in the gastræads,
the turbellaria, the rotifera, the nemertina, and the young larvæ
of many other metazoa. The vibratory apparatus reaches its highest
development in the _ctenophora_. The extremely delicate and soft body
of these gherkin-shaped cnidaria swims slowly in the water by means
of the strokes of thousands of tiny oar-blades. They are arranged in
eight longitudinal rows which stretch from the mouth to the opposite
pole. Each oar-blade consists of the long hair-lashes of a group of
epithelial cells glued together.
The chief motor organs in the metazoa are the muscles which constitute
the "flesh" of the body. Muscular tissue consists of contractile
cells--that is to say, of cells with the sole property of contraction.
When the muscular cell contracts, it becomes shorter and its diameter
increases. This brings nearer together the two parts of the body to
which its ends are attached. In the lower metazoa the muscle-cells
have, as a rule, no particular structure; but in the higher animals the
contractile plasm undergoes a peculiar differentiation, which has the
appearance under the microscope of a transverse streaking of the long
cells. On this ground a distinction is drawn between striated muscles
and simple non-striated or smooth muscles. The more vigorous, rapid,
and definite is the contraction of the muscle, the more marked is the
streaky character, and the more pronounced the difference between the
doubly refractive muscular particles from the simple refractive. The
striated muscle is "the most perfect dynamo we know of" (Verworn). The
normal heart of a man accomplishes every day, according to Zuntz, a
work of about twenty thousand kilogrammetres--in other words, an energy
that would suffice to lift to a height of one metre a weight of twenty
thousand kilogrammes. In many flying insects (gnats, for instance) the
flying muscles make three hundred to four hundred contractions a second.
In the lower and higher classes of the metazoa the muscle amounts to
no more than a thin layer of flesh underneath the skin. This layer
consists of muscular cells, which come originally from the ectoderm
in the form of internal contractile processes of the skin-cells
themselves, as in the polyps. In other cases the muscle-cells are
developed from the connective-tissue cells of the mesoderm, the
middle skin-layer, as in the ctenophora. This mesenchymic muscle is
less common than epithelial muscle. In most of the askeletal vermalia
the subdermal muscle divides into two layers--an outer deposit of
concentric muscles and an inner layer of longitudinal muscles; in the
cylindrical worms (nematodes, sagittæ, etc.) the latter fall into
four longitudinal bands, one pair of upper (dorsal) and a pair of
lower (ventral) muscular bands. At those parts of the body which are
especially used for locomotion the muscle is more strongly developed,
as in the belly-side of the crawling worms and mollusks. This muscular
surface develops into a kind of fleshy "foot" (_podium_); it assumes
a great variety of forms in the various classes of mollusks. In most
of the snails which creep on the solid ground it grows into a muscular
"flat-foot" (_gasteropoda_); in the mussels which cut like a plough
through the soft slime it forms a sharp "hatchet-foot" (_pelecypoda_).
The keel-snails (_heteropoda_) swim by means of a "keel-foot," which
works like the screw of a ship; the floating-snails (_pteropoda_) swim
unsteadily (like butterflies flying) by means of a pair of head-folds,
which develop from the side of the anterior foot-section. In the
highest mollusks, the cuttle-fishes (_cephalopoda_), this fore-foot
divides into four or five pairs of folds, which grow into long and very
muscular "head-arms"; the numbers of strong suckers on the latter have
also special muscles. In all these non-articulate mollusks and vermalia
hard skeletons are either altogether wanting or (like the external
shells of the mollusks) they have no functional relation to the motor
muscles. It is otherwise in the higher animals, in which we find this
relation to a solid jointed skeleton that becomes a passive motor
apparatus.
The higher groups of the animal kingdom in which a characteristic solid
skeleton is developed and forms an important starting-point for the
muscles, as well as a support and protection for the whole body, are
the three stems of the echinoderms, articulates, and vertebrates.
All three groups are very rich in forms, and far surpass all the
other stems of the animal world in the perfection of their locomotive
apparatus. However, the disposition and development of the skeleton as
a passive support, and the correlation of the muscles to it as active
pulling-organs, differ very much in the three classes, and are the
chief factors in determining their characteristic types; they show
clearly (even apart from other radical differences) that the three
stems have arisen independently of each other from three different
roots in the vermalia-stem. In the echinoderms the calcareous skeleton
is formed from chalky deposits in the corium, in the articulates from
chitine secretions of the epidermis, and in the vertebrates from
cartilage of an internal chord-sheath (_cf._ _Anthropogeny_, chapter
xxvi.).
The remarkable stem of the sea-dwelling echinoderms or "prickly skins"
is distinguished from all the other animal groups by a number of
striking peculiarities; prominent among these are the special formation
of their active and passive motor organs and the curious form of their
individual development. In this ontogenesis two totally different
forms appear successively--the simple astrolarva and the elaborately
organized and sexually mature astrozoon. The small, free-swimming
astrolarva has the general structural features of the rotatoria, and
so shows, in accordance with the biogenetic law, that the original
stem-form of the echinoderms (the amphoridea) belonged to this group
of the vermalia. I have briefly explained these structures in the
_History of Creation_ (chapter xxii.), and more fully in my essay on
the amphoridea and cystoidea (1896). The little astrolarva has no
muscles, and no water-vessels or blood-vessels. It moves by means
of vibratory lashes or bands, which are attached to special armlike
processes at the surface. These arms are regularly developed to the
right and left of the bilateral symmetrical larva (which as yet shows
no trace of the five-rayed structure). By a very curious modification
the small bilateral astrolarva is transformed into the totally
different pentaradial astrozoon, the large sexually mature echinoderm
with a pronounced five-rayed structure. (See _Art-forms in Nature_,
plates 10, 20, 30, 40, 60, 70, 80, 90, and 95.) It has a most elaborate
organization, with muscles and cuticular skeleton, blood-vessels and
water-vessels, etc. A section of the astrozoa--the living crinoidea,
or sea-lilies, and the extinct classes of blastoidea (sea-buds),
cystoidea (sea-apples), and amphoridea (sea-urns)--grow in stationary
fashion at the bottom of the sea. The other four extant classes
creep about in the sea--the sea-gherkins (holothuria), the star-fish
(asteridea and ophoidea), and the sea-urchins (echinidea). Their
creeping motion is accomplished by two kinds of organs--water-feet
and skin-muscles. The latter find their support and attachment in
solid calcareous needles, which develop from chalky deposits in the
corium. As these calcareous needles (which are particularly conspicuous
in the sea-urchin) are set movably in special protuberances of the
calcareous plates of the cuticular skeleton, and moved by little
muscular needles, the echinoderms walk on them as if they were stilts.
Between these, however, a number of water-feet arise from inside--thin
tubes like the fingers of a glove, which are filled with water by
an internal conduit-system (the so-called ambulacral system) and
become stiff. These very extensible ambulacral feet, often provided
with a suctorial plate at the closed outer end, serve for creeping,
sucking, touching, and grasping. As these distinctive motor organs
of the echinoderms--both the ambulacral feet with their complicated
water-tubes and the movable needles with their joints and muscles--are
found in hundreds, often in thousands, on every individual five-rayed
astrozoon, we might say that the echinoderms have the most advanced
and complicated motor organs of all animals. Their historical
development is perfectly understood from its earliest stages, since
Richard Semon found, in his ingenious pentact æatheory (1888),
the correct phylogenetic meaning of the curious embryology of the
echinoderms discovered in 1845 by Johannes Müller. I endeavored in 1896
to establish it in detail, in relation to paleontological discoveries,
in the essay I have mentioned.
The large stem of the articulata (the richest in forms of all the
animal stems) comprises three chief classes--the annelids, crustacea,
and tracheata. All three groups agree in the essential features
of their organization, especially in the external articulation or
metamerism of the long bilateral body, and also in the repetition of
the internal organs in each joint or segment. In each joint there is
originally a knot of the ventral nervous system (the ventral marrow), a
chamber of the dorsal heart, a chitine-ring of the cutaneous skeleton,
and a corresponding group of muscles.
Of the three great classes of the articulates the annelids are
developed directly from the vermalia, of which both the nematoda and
nemertinæ approach very closely to them. The two other and more highly
organized classes, the crustacea and tracheata, are younger groups,
independently evolved from two different stems of the annelids. The
annelids, or "ringed-worms" (to which, _e.g._, the rain-worms belong),
have mostly a very homogeneous articulation; their segments or metamera
repeat the same structure to a great extent, especially the subdermal
muscles. In a transverse section we see in every joint underneath the
layer of concentric muscles a pair of dorsal and a pair of ventral
muscles. Their epidermis has secreted a thin covering of chitine, in
the tubular worms a leather-like or calcified tube. There are no bones
in the oldest annelids; in the younger bristle-worms (_polychæta_) one
or two pairs of short unjointed feet (_parapodia_) are found in every
joint.
The other two chief classes of the articulates develop long and jointed
feet of very varied forms, and at the same time assume different shapes
of limbs in the division of labor. This heterogeneous articulation
(heteronomy) is the more pronounced the higher the whole organization.
This is equally true of the aquatic, gill-breathing crustacea (crabs,
etc.) and the tracheata (terrestrial animals breathing through a
trachea, the myriopods, spiders, and insects). In the higher groups of
both classes the number of limbs is usually not higher than fifteen to
twenty; and they are distributed in three principal sections--head,
breast, and posterior part of the body. The firm covering of chitine,
which was delicate and thin in most of the annelids, is much thicker in
most of the crustacea and tracheata, and often hardened by a calcareous
deposit; it forms a solid ring of chitine in each segment, inside which
the motor muscles are attached. The successive hard rings are connected
by thin, mobile, intermediate rings, so that the whole body combines
firmness, elasticity, and mobility in a high degree. The structure of
the long jointed legs, which are fixed in pairs on each segment, is
very similar. Hence the typical character of the motor organs of the
crustacea lies in the circumstance that both in the body and the limbs
the muscles are attached to the interior of hollow chitine tubes, and
go in these from member to member.
The vertebrates are just the reverse in structure. In their case
a solid internal skeleton is formed in the longitudinal axis of
the body, and the muscles are external to these supporting organs.
The articulation or metamerism itself is not visible externally in
the vertebrates; it is only seen in the muscular system when the
non-articulated skin has been removed. Then, even in the lowest
skull-less vertebrates, the acrania, the internal skeleton of which
consists merely of a cylindrical, solid, and elastic axial rod
(_chorda_), we see on each side a row of muscular plates (fifty to
eighty in the amphioxus). In this case there are not pairs of limbs,
and it is the same with the oldest craniate animals, the cyclostoma
(myxinoida and petromyzonta). It is only with the third class of the
vertebrates, the true fishes (_pisces_), that two pairs of lateral
limbs appear--the breast-fins and belly-fins. From these, in their
terrestrial descendants, the oldest amphibia of the Carboniferous
Period, the two pairs of jointed legs--fore-legs (carpomela) and
hind-legs (tarsomela)--are derived. These four lateral five-toed legs
have a very characteristic and complicated articulation, both in the
internal bony skeleton and the muscular system that encloses this and
is attached to it. From the amphibia, the earliest quadrupeds, this
locomotive apparatus is transmitted by heredity to their descendants,
the three higher classes of the vertebrates, reptiles, birds, and
mammals. As I have dealt with these important structures fully in my
_Anthropogeny_ (chapter xxvi.), and given a number of illustrations of
them, I must refer the reader to that work,[8] and will only make a few
observations on the mammals.
Both parts of the motor apparatus, the internal bony skeleton (the
passive supporting apparatus) and the external muscular system (the
active motor), exhibit a great variety of construction within the
mammal class, in consequence of adaptation to the most different
habits and functions. We have only to compare the running carnivora
and ungulata, the leaping kangaroos and jerboas, the burrowing moles
and hyperdæi, the flying cheiroptera and bats, the fishlike swimming
sirens and whales, and climbing lemures and apes. In all these and the
remaining orders of the mammals the whole regular structure of the
motor apparatus is strikingly adapted to the habits of life which have
been formed by this adaptation itself. Nevertheless, we see that the
essential character of the inner organization which distinguishes the
mammals as a class is not affected by this adaptation, but constantly
maintained by heredity. These recognized facts of comparative anatomy
and ontogeny, and the concordant results of paleontology, prove
convincingly that all living and fossil mammals, from the lowest
ungulates and marsupials to the ape and man, have descended from one
common stem-form, a pro-mammal, that lived in the Triassic Period;
its earlier ancestors in the Permian Period were reptiles, and, in
the Carboniferous Period, amphibia. Among the characters of the
locomotive apparatus which are peculiar to mammals we have, on the
one hand, the structure of the vertebral column and the skull, and,
on the other hand, the formation of the muscles which are attached
to these supporting organs. In the skull we particularly notice the
formation of the lower jaw and the joint by which it is connected with
the temporal bone. This joint is temporal, and so distinguished from
the square joint of the other vertebrates. The latter is found in the
mammals in the tympanic cavity of the middle-ear, between the hammer
(the modified joint of the lower jaw, _articulare_) and the anvil (the
original _quadratum_). In harmony with this remarkable modification
of the maxillary joint, the corresponding muscles have naturally
also undergone a considerable transformation. A distinctive muscle
that is only found in the mammals and regulates their respiration is
the diaphragm, which completely divides the abdominal and thoracic
cavities; the various muscles, from the blending of which it has been
formed, still remain separate in the other vertebrates.
The many organs by means of which our human organism accomplishes its
manifold movements are just the same as in the apes, and the mechanism
of their action is in no way different. The same two hundred bones,
in the same order and composition, form our internal bony skeleton;
the same three hundred muscles effect our movements. The differences
we find in the form and size of the various muscles and bones (and
which are, as is well known, also found between lower and higher
races of men) are due to differences in growth in consequence of
divergent adaptation. On the other hand, the complete agreement in the
construction of the whole motor apparatus is explained by heredity from
the common stem-form of the apes and men. The most striking difference
between the movements of the two is due to man's adaptation to the
erect posture, while the climbing of trees is the normal habit of the
ape. However, it is unquestionable that the former is an evolution
from the latter. A double parallel to this modification is seen in the
jerboa among the ungulates, and in the kangaroo among the marsupials.
Both these, in springing, use only the strong hinder extremities, and
not the weaker fore-limbs; as a result of this their posture has become
more or less erect. Among the birds we have an analogous case in the
penguins (_aptenodytes_); as they no longer use their atrophied wings
for flight, but only in swimming, they have developed an erect posture
when on land.
The human will is also not specifically different from that of the ape
or any other mammal; and its microscopic organs, the neurona in the
brain and the muscular cells in the flesh, work with the same forms
of energy, and are similarly subject to the law of substance. Hence
it is immaterial for the moment whether one believes in the freedom
of the will according to the antiquated creed of indeterminism, or
whether one holds it to be refuted scientifically by the arguments
of modern determinists; in either case the acts of the will and
voluntary movements follow the same laws in man as in the ape. The high
development of the function in civilized man, the ample differentiation
of speech and morality, art and science--in a word, the ethical
significance of the will for higher culture--is in no way discordant
to this monistic and zoologically grounded conception. In the lower
races these privileges of the civilized will are only found in a slight
degree, and some of them are wholly wanting among the lowest races. The
distance between the lowest savage and the most civilized human being
is greater, in this respect also, than that which separates the savage
from the anthropoid ape. However, I refer the reader to the remarks
I made at the close of the seventh chapter of the _Riddle_ on the
problem of the freedom of the will and the infinite literature relating
thereto. The reader who desires to go further into this subject will
find it well treated in the works of Traugott Trunk (1902) and Paul Rée
(1903) [also in Dr. Stout's recent little manual of psychology and Mr.
W. H. Mallock's _Religion as a Credible Doctrine_].
XIII
SENSATION
Sensation and consciousness--Unconscious and conscious
sensation--Sensibility and irritability--Reflex sensation and
perception of stimuli--Sensation and living force--Reaction
to stimuli--Resolution of stimuli--External and internal
stimuli--Conveyance of stimuli--Sensation and striving--Sensation
and feeling--Inorganic and organic sensation--Light sensation,
phototaxis, sight--Sensation of warmth, thermotaxis--Sensation of
matter, chemotaxis--Taste and smell--Erotic chemicotropism--Organic
sensations--Sensation of pressure--Geotaxis--Sensation of
sound--Electric sensation.
Sensation is one of those general terms that have at all times been
liable to the most varied interpretations. Like the cognate idea of
the "soul," it is still extremely ambiguous. During the eighteenth
century it was generally believed that the function of sensation was
peculiar to animals, and was not present in plants. This opinion found
its most important expression in the well-known principle in Linné's
_Systema Naturæ_: "Stones grow: plants grow and live: animals grow,
live, and feel." Albrecht Haller, who gathered up all the knowledge
of his time relating to organic life in his _Elementa Physiologiæ_
(1766), distinguished as its two chief characters "sensibility" and
"irritability." The one he ascribed exclusively to the nerves, and the
other to the muscles. This erroneous idea was subsequently refuted, and
in our own time irritability is conceived to be a general property of
all living matter.
The great advance made by the comparative anatomy and experimental
physiology of animals and plants in the first half of the nineteenth
century brought to light the fact that irritability or sensibility is
a common quality of all organisms, and that it is one of the principal
characteristics of vital force (_cf._ chapter ii.). The greatest merit
in connection with its experimental study attaches to the famous
Johannes Müller. In his classical _Manual of Human Physiology_ (1840)
he established his theory of the specific energy of the nerves and
their dependence on the sense-organs on the one hand and the mental
life on the other. He devoted the fifth chapter of his book to the
former and the sixth to the latter, approaching particularly to
Spinoza in his general psychological views; he treated psychology as
a part of physiology, and thus put on a sound scientific basis that
naturalistic conception of the place of psychology in the biological
system which we now regard as the correct view. At the same time he
proved that sensation is a function of the organism as much as movement
or nutrition.
The view of sensation that prevailed in the second half of the
nineteenth century was very different. On the one hand the experimental
and comparative physiology of the sense-organs and the nervous system
immensely enriched our exact knowledge by the invention of ingenious
methods of research and the use of the great advance made by physics
and chemistry. The famous investigations of Helmholtz and Hertwig on
the physics of the senses, of Matteucci and Dubois-Reymond on the
electricity of the muscles and nerves, and the great progress made in
vegetal physiology by Sachs and Pfeffer, and in physiological chemistry
by Moleschott and Bunge, enabled us to realize that even the most
mysterious of the wonders of life depend on physical and chemical
processes. By the application of the different stimuli--light, heat,
electricity, and chemical action--to the various sensitive or irritable
organs under definitely controlled conditions, scientists succeeded in
subjecting with exactness a great part of the phenomena of stimulation
to mathematical measurements and formulæ. The science of the stimuli
and their effects acquired a strictly physical character.
On the other hand, in most striking contradiction to the immense
advance of experimental physiology, we see that the general
conception of the various vital processes, and especially of the
inner nerve-action that converts the functions of the senses into
mental life, is most curiously neglected. Even the fundamental idea
of sensation, which plays the chief part in it, is disregarded more
and more. In many of the most valuable modern manuals of physiology,
containing long chapters on stimuli and stimulation, there is little or
no mention of sensation as such. This is chiefly due to the mischievous
and unjustifiable gulf that has once more been artificially created
between physiology and psychology. As the "exact" physiologists
found the study of the inner psychic processes which take place in
sense-action and sensation inconvenient and unprofitable, they gladly
handed over this difficult and obscure field to the "psychologists
proper"--in other words, to the metaphysicians, who had for the
starting-point of their airy speculations the belief in an immortal
soul and divine consciousness. The psychologists readily abandoned the
inconvenient burden of experience and _a posteriori_ knowledge, to
which the modern anatomic physiology of the brain laid special claim.
The greatest and most fatal error committed by modern physiology in
this was the admission of the baseless dogma that all sensation must
be accompanied by consciousness. As most physiologists share the view
of Dubois-Reymond, that consciousness is not a natural phenomenon,
but a hyperphysical problem, they leave it and this inconvenient
"sensation" outside the range of their researches. This decision is,
naturally, very agreeable to the prevalent metaphysics; it has just as
much interest in the transcendental character of sensation as in the
liberty of the will, and thus the whole of psychology passes from the
empirical province of natural science into the mystical province of
mental science. For its foundation they then take the "critical theory
of knowledge," which ignores the results of the real physiological
organs--the senses, nerves, and brain--and draws its "superior wisdom"
from the inner mirroring of self by the introspective analysis of
presentations and their associations. It is extraordinary that even
distinguished monistic physiologists suffer themselves to be taken
in with this sort of metaphysical jugglery, and dismiss the whole of
psychology from their province; their psychomonism readmits the soul as
a supernatural entity, and delivers it, in contrast with the "world of
bodies," from the yoke of the law of substance.
Impartial reflection on our personal experience during sensation and
consciousness will soon convince us that these are two different
physiological functions, which are by no means necessarily associated;
and the same may be said of the third principal function of the
soul--the will. When we learn an art--for instance, painting or
playing the piano--we need months of daily practice in order to become
expert at it. In this we experience every day hundreds of thousands
of sensations and movements which are learned and repeated with full
consciousness. The longer we continue the practice and the more we
adapt and accustom ourselves to the function, the easier and less
conscious it becomes. And when we have practised the art for some
years, we paint our picture or play our piano unconsciously; we think
no longer of all the small, subtle shades of sensation and acts of
will which were necessary in learning. The mere impulse of the will to
paint the picture once more or play the piece again suffices to release
the whole chain of complicated movements and accompanying sensations
which had originally to be learned slowly, laboriously, and with
full consciousness. An experienced pianist plays the most difficult
piece--if he has learned it and repeated it thousands of times--"half
in a dream." But it needs only a slight accident, such as a mistake
or a sudden interruption, to bring back the wandering attention to
the work. The piece is now played with clear consciousness. The same
may be said of thousands of sensations and movements which we learned
at first consciously in childhood, and then repeat daily afterwards
without noticing--such as in walking, eating, speaking, and so on.
These familiar facts prove of themselves that consciousness is a
complicated function of the brain, by no means necessarily connected
with sensation or will. To bind up the ideas of consciousness and
sensation inseparably is the more absurd, as the mechanism or the real
nature of consciousness seems very obscure to us, while the idea of it
is perfectly clear: we know that we know, feel, and will.
The word "irritability" is generally taken by modern physiology to mean
that the living matter has the property of reacting on stimuli--that
is to say, of responding by changes in itself to changes in its
environment. The stimulus, or action of a foreign energy, must,
however, be felt by the plasm before the corresponding stimulated
movement (in the form of various manifestations of energy) will be
produced. Hence the question whether this sensation is (in certain
cases) associated with consciousness or (generally) remains unconscious
is of a subordinate interest. The plant that is caused to open its
floral calyx by the stimulus of light acts just as unconsciously in
this as the coral that spreads out its crown of tentacles under the
same influence; and when the sensitive carnivorous plant (_dionæa_ or
_drosera_) closes its leaves in order to catch and destroy the insect
sitting on them, it acts in the same way as the sensitive actinia or
coral when it draws in its crown of tentacles for the same object--in
both cases without consciousness! We call these unconscious movements
"reflex actions." I have dealt somewhat fully with these reflex
movements in the seventh chapter of the _Riddle_, and must refer the
reader thereto. This elementary psychic function always depends on
a conjunction of sensation and movement (in the widest sense). The
movement that the stimulus provokes is always preceded by a sensation
of the influence exerted.
Modern physiology makes desperate efforts to avoid the use of the
word "sensation" and substitute for it "perception of stimulus." The
chief blame for this misleading expression is due to the arbitrary
and unjustified separation of psychology from physiology. The latter
is supposed to occupy itself with the material phenomena and physical
changes, leaving to psychology the privilege of dealing with the
higher mental phenomena and metaphysical problems. As we reject this
distinction altogether on monistic principles, we cannot consent
to separate sensation from the perception of stimuli--whether this
sensation be accompanied with consciousness or not. Moreover, modern
physiology, in spite of its desire to keep clear of psychology, sees
itself compelled in a thousand ways to use the words "sensation" and
"sensitive," especially in the science of the organs of sense.
What we call sensation or perception of stimuli may be regarded
as a special form of the living force or actual energy (Ostwald).
Sensitiveness or irritability, on the other hand, is a form of virtual
or potential energy. The living substance at rest, which is sensitive
or irritable, is in a state of equilibrium and indifference to its
environment. But the active plasm, that receives and feels a stimulus,
has its equilibrium disturbed, and corresponds to the change in its
environment and its internal condition. This response of the organism
to a stimulus is called "reaction"--a term that is also used (in
the same sense) in chemistry to express the interaction of bodies
on each other. At each stimulation the virtual energy of the plasm
(sensitiveness) is converted into living or kinetic force (sensation).
The share of the stimulus in this conversion is described as a
"release" of energy.
The term "reaction" stands in general for the change which any body
experiences from the action of another body. Thus, for instance, to
take the simplest case, the interaction of two substances in chemistry
is called a reaction. In chemical analysis the word is used in a
narrower sense to denote that action of one body on another which
serves to reveal its nature. Even here we must assume that the two
bodies feel their different characters; otherwise they could not act
on each other. Hence every chemist speaks of a more or less "sensitive
reaction." But this process is not different in principle from the
reaction of the living organism to outer stimuli, whatever be their
chemical or physical nature. And there is no more essential difference
in psychological reaction, which is always bound up with corresponding
changes in the psychoplasm, and so with a chemical conversion of
energy. In this case, however, the process of reaction is much more
complicated, and we can distinguish several parts or phases of it:
1, the outer excitation; 2, the reaction of the sense-organ; 3, the
conducting of the modified impression to the central organ; 4, the
internal sensation of the conducted impression; and, 5, consciousness
of the impression.
The important idea of a release of energy--the term we give to the
effect of the stimulus--is also used in physics. If we put a piece of
burning wood in a barrel of powder, the flame causes an explosion. In
the case of dynamite a simple mechanical shock is enough to produce
the most enormous expenditure of force in the explosive matter. When
we discharge a bow the slight pressure of the finger on the tense
cord suffices to send out the arrow or bolt on its deadly mission. So
also a sound or a ray of light that strikes the ear or eye suffices
to bring about a number of complex effects by means of the nervous
system. In the fertilization of the ovum by the male sperm the chemical
conjunction of the two formative principles is sufficient to cause the
growth of a new human being out of the microscopic plasma-globule, the
stem-cell (_cytula_). In these and thousands of other reactions a very
slight shock suffices to provoke the largest effects in the stimulated
substance. This shock, which we call a release of energy, is not the
direct cause of the considerable result, but merely the occasion for
bringing it about. In these cases we have always a vast accumulation
of virtual energy converted into living force or work. The magnitude
of the two forces has no relation at all to the smallness of the shock
which led to the conversion. In this we have the difference between
stimulated action and the simple mechanical action of two bodies on
each other, in which the quantity of the energy expended is equal on
both sides, and there is no stimulus.
The immediate effect of a stimulus on living matter can best be
followed in external physical or chemical stimuli, such as light,
heat, pressure, sound, electricity, and chemical action. In these
cases physical science is often able to reduce the life-process to the
laws of inorganic nature. This is more difficult with the internal
stimuli within the organism itself, which are only partly exposed
to physiological investigation. It is true that here also the task
of science is to reduce all the biological phenomena to physical and
chemical laws. But it can only discharge a part of this difficult task,
as the phenomena are too complicated, and their conditions too little
known in detail, to say nothing of the crudeness and imperfectness of
our methods of research. Yet, in spite of all this, comparative and
phylogenetic physiology convinces us that even the most complicated
of our internal excitations, and particularly the mental activity of
the brain, depend just as much as the outer stimulations on physical
processes, and are equally subject to the law of substance. This is, in
fact, true of reason and consciousness.
In man and all the higher animals the stimuli are received by the
organs of sense and conducted by their nerves to the central organ. In
the brain they are either converted into specific sensations in the
sense-centres, or conveyed to the motor region, where they provoke
movements. The conduction of stimuli is simpler in the lower animals
and the plants; the tissue-cells either directly affect each other or
are connected by fine threads of plasm. In the unicellular protists
the stimulus which strikes one particular spot of the surface may be
immediately communicated to the other parts of the unified plasmic body.
We shall see in the course of our inquiry that the simplest form of
sensation (in the widest sense) is common to inorganic and organic
bodies, and thus that sensitiveness is really a fundamental property
of all matter, or, more correctly, all substance. We may, therefore,
ascribe sensation to the constituent atoms of matter. This fundamental
thought of hylozoism, expressed long ago by Empedocles, has lately
been very definitely urged, especially by Fechner. However, the able
founder of psychophysics (_cf._ the _Riddle_, p. 35) assumes that
consciousness (or thought, in the Spinozistic sense) always accompanies
this universal property of sensation. In my opinion, consciousness is a
secondary psychic function, only found in man and the higher animals,
and bound up with the centralization of the nervous system. Hence it is
better to speak of the unconscious sensation of the atoms as _feeling_
(_æsthesis_), and their unconscious will as _inclination_ (_tropesis_).
It finds expression in the one-sided action of a stimulus as a
"directed movement" or "stimulated movement" (_tropismus_ or _taxis_).
The familiar ideas of sensation and feeling are often confused, and
employed in very different ways in both physiology and psychology. The
metaphysical tendency which so completely separates the two sciences,
and the physiological tendency which agrees with it, regard feeling
as a purely psychic or spiritual function, whereas in the case of
sensation they have to admit the connection with bodily functions,
especially sense-action. In my opinion, the two ideas are purely
physiological and cannot be sharply separated, or only in the sense
that sensation relates more to the external (objective) part of the
sensory nerve-process, and feeling to the internal (subjective) part.
Hence we may define the difference in a general way by saying that
sensation perceives the different qualities of the stimuli, and feeling
only the quantity, the positive or negative action of the stimulus
(pleasure or pain). In this last and widest sense we may ascribe
the feeling of pleasure and pain (in the contact with qualitatively
differing atoms) to all atoms, and so explain the elective affinity in
chemistry (synthesis of loving atoms, inclination; analysis of hating
atoms, disinclination).
Our monistic system (whether it be taken as energism or materialism,
or more correctly as hylozoism) regards all substance as having
"soul"--that is to say, endowed with energy. In the chemical analysis
of organisms we do not find any elements that are not found in
inorganic nature; we find that the movements in organisms obey the
same laws of mechanics as the latter; we believe that the conversion
of energy in the living matter occurs in the same way, and is provoked
by the same stimuli, as in inorganic matter. We are forced to conclude
from. these experiences that the perception of stimuli--sensation in
the objective and feeling in the subjective sense--is also generally
present in the two. All bodies are in a certain sense "sensitive." It
is just in this dynamic conception of substance that monism differs
essentially from the materialistic system, which regards one part of
matter as "dead" and insensitive. In this we have the best means of
joining consistent materialism or realism with consistent spiritualism
or idealism. But, as a first condition of such a union, we must demand
a recognition that organic life is subject to the same general laws
as inorganic nature. In both cases the outer world acts alike as
a stimulus on the inner world of the body. We can easily see this
if we glance at the various kinds of sensation which correspond to
the various kinds of stimuli. Light and heat, external and internal
chemical stimuli, pressure and electricity, cause analogous sensations
and modifications in their effect on organic and inorganic bodies.
The effect which the light-stimulus has on living matter, the sensation
of light that results, and the chemical changes of energy that follow,
are of great physiological importance in all organisms. We might even
say that sunlight is the first, oldest, and chief source of organic
life; all other exertions of force depend in the long run on the
radiant energy of sunlight. The oldest and most important function
of plasm--one which is at the same time a cause of its formation--is
carbon-assimilation; and this plasmodomism is directly dependent on
sunlight. If it acts in a one-sided way, it causes the particular form
of stimulation which we call phototaxis or heliotropism. This is of a
positive character--that is to say, they turn towards the source of the
light--in the great majority of organisms, both protists and histona.
Everybody knows that flowers that are growing in the window of a room
turn to the light. However, many organisms which have grown accustomed
to living in the dark are heliotropically negative; they shun the light
and seek darkness, such as the fungi, many lucifugous mosses and ferns,
and many deep-sea animals.
The principal organs of light-sensation in the higher animals are the
eyes; they are wanting in many of the lower animals as well as the
plants. The essential difference between the real eye and a part of
the skin that is merely sensitive to light is that the eye can form a
picture of objects in the outer world. This faculty of vision begins
with the formation of a small convergent lens, a biconvex refracting
body at a certain spot on the surface. Dark pigment-cells which
surround it absorb the light-rays. From this first phylogenetic form of
the organ of vision up to the elaborate human eye there is a long scale
of evolutionary stages--not less extensive and remarkable than the
historical succession of artificial optical instruments from the simple
lens to the complicated modern telescope or microscope. This great
"wonder of life"--the long scale of the evolution of the eye--has an
interesting tearing on many important questions of general physiology
and phylogeny. We can, in this case, see clearly how a very complicated
and purposive apparatus can arise in a purely mechanical way, without
any preconceived design or plan. In other words, we can see how an
entirely new function--and one of its principal functions, vision--has
arisen in the organism by mechanical means.
The advanced vision of the higher animals is made up of a great number
of different functions, with a corresponding complexity of detail in
the anatomic structure of the eye. No other organ, after the brain,
is so necessary as the eye for the multifarious vital activities of
the higher animals, and especially for the mental life of civilized
man and the progress of art and science. What would the human mind be
if we could not read, write, and draw, and have a direct knowledge
through the eye of the forms and colors of the outer world? Yet this
invaluable structure is only the highest and most perfect stage in
the long chain of evolutionary processes which has its starting-point
in the general sensitiveness to light, or the photic irritability of
plasm. However, we find a number of varieties and grades of this even
among the unicellular protists, and, indeed, the very lowest and oldest
of the protists, the monera. Various species of both the chromacea and
the bacteria are heliotropic to different degrees, and have a fine
sensitiveness to the strength of the light stimulus.
The stimulating effect which light has on the homogeneous plasm of the
monera is also found in a number of inorganic bodies. In these cases
the photic stimulus produces partly chemical and partly mechanical
changes. Every chemist speaks of substances that are more or less
"sensitive" to light; the photographer speaks of his "sensitive
plates," the painter of his "sensitive colors." Many chemical compounds
are so sensitive to light that they are destroyed at once in sunlight,
and so have to be kept in the dark. There is no other word but
"sensation" to express the attitude of the atoms towards each other
which becomes so conspicuous in these cases under the influence of
sunlight. It seems to me that this phenomenon is a clear justification
of our hylozoic monism when it affirms that all matter is psychic. In
metaphysics sensation is held to be an essential property of the soul.
In the same general way as light the heat-stimulus acts on organisms,
and causes the sensations, sometimes pleasant and sometimes unpleasant,
which we call the subjective feeling of heat, warmth, coolness, or
cold. The sense-organ that receives these impressions of temperature is
the surface of the unicellular plasmic body in the protists, and the
skin (epidermis) that protects the surface from the outer world in the
histona. In all living things the temperature of the surrounding medium
(water or air) has a great influence in regulating the life-processes;
in the stationary animals and plants it is the temperature of the
ground to which they are attached. This temperature must always be
between the freezing-point and boiling-point of water, as fluid water
is indispensable for the imbibition of the living matter and the
molecular movements within the plasm. At the same time, some of the
lower protists (chromacea, bacteria) can endure very high and very
low temperatures, but only for a short time. Some protists (monera
and diatomes) can stand a temperature of 200° C. for several days,
and others can be heated above boiling-point without being killed.
Arctic and High-Alpine plants and animals may be in a frozen condition
for several months, yet live again when they are thawed. However, the
resistance to these extremes of cold lasts for only a limited time, and
in the frozen state all vital functions are at a standstill.
In the great majority of living things the vital activity is confined
within narrow limits of temperature. Many plants and animals in the
tropics which have been accustomed for thousands of years to the
constancy of the hot equatorial climate can endure only very restricted
variations of temperature. On the other hand, many of the inhabitants
of Central Siberia, where the climate is very hot in the short summer
and very cold in the long winter, can stand great variations. Thus
the living plasm has experienced considerable changes in its sense
of warmth through adaptation to different environments; not only the
maximum and the minimum, but the optimum (most agreeable point),
is subject to very great variations. This can easily be observed
and followed experimentally in the phenomena of thermotaxis or
thermotropism--that is to say, the effect that follows from a one-sided
action of the heat-stimulus. The organism that falls below the minimum
of temperature is said to be stiff with cold, while the organism that
rises above the maximum is stiff with heat.
The heat-stimulus acts on inorganic as well as organic bodies, like
the light-stimulus. The law holds good in both cases that higher
temperatures increase sensation, while lower ones paralyze it. There is
a minimum, an optimum, and a maximum, for many chemical and physical
processes in the inorganic world. As far as the melting effect of water
is concerned, freezing is the minimum of the heat stimulus and boiling
the maximum. As the various chemical compounds meet in water at very
different temperatures, we have an optimum for many substances--that is
to say, a degree of warmth which is most favorable to the solution of
a given quantity of a solid body in water. On the whole, the law holds
for chemical processes that they are accelerated by high temperatures
and retarded by low ones (like the human passions!); the former have
a stimulating and the latter a benumbing effect. As the action of the
various chemical compounds on each other is determined by the nature
of the elements and their affinities, we must trace the variations in
their conduct towards thermic stimuli to a sensation of temperature in
the constituent atoms; increase of temperature stimulates it, while
decrease lessens or paralyzes it. Here, again, the simple inorganic
processes have a general resemblance to the complicated vital phenomena
in the organic body.
Since we regard the whole of organic life as, in the ultimate analysis,
merely a very elaborate chemical process, we shall quite expect that
chemical stimuli are the most important factors in sensation. And this
is so in point of fact; from the simplest moneron up to the most highly
differentiated cell and on to the flower in the plant and the mental
life of man, the vital processes are dominated by chemical forces and
conversions of energy, which are set in play by external or internal
chemical stimuli. The excitation which they produce is called, in a
general way, "sensation of matter" or chemæsthesis; the basis of it
is the mutual relation of the chemical elements which we describe as
chemical affinity. In this affinity we have the play of attractive
forces which lie in the nature of the elements themselves, especially
in the peculiar properties of their constituent atoms; and this cannot
be explained unless we ascribe unconscious sensation (in the widest
sense) to the atoms, an inherent feeling of pleasure and the reverse,
which they experience in the contact of other atoms (the "loves and
hatreds of the elements" of Empedocles).
The numbers of different stimuli that act chemically on the plasm
and excite its "sensation of matter" may be divided into two
groups--external and internal stimuli. The latter lie within the
organism itself, and cause the internal "organic sensations";
the former are in the outer world, and are felt as taste, smell,
sex-impulse, etc. In the higher animals special chemical sense-organs
have been developed for these chemical stimuli. As these are well known
to us from our own human experience, and comparative physiology shows
us the same structures in the higher animals, we will deal first with
them. In general the same law holds for these external chemical stimuli
as for optical and thermic stimuli; we can recognize a maximum limit
of their action, a minimum below which they fail to stimulate, and an
optimum or stage in which their influence is strongest.
The important part played in human life by taste and the pleasure
associated with it is well known. The careful choice and preparation
of savory food--which has become an art in gastronomy and a branch
of practical philosophy in gastrosophy--was just as important two
thousand years ago with the Greeks and Romans as it is to-day in royal
banquets or the Lucullic dinners of millionaires. The excitement that
we see associated with this refined combination of rich foods and
drinks, and that finds expression in so many speeches and toasts, has
its philosophic root in the harmony of gustatory sensations and the
varying play of stimuli that the delicate dishes and wines exercise
on the organs of taste, the tongue and palate. The microscopic organs
of these parts of the mouth are the gustatory papillæ--cup-shaped
structures, covered with spindle-shaped "taste-cells," and having a
narrow opening into the cavity of the mouth. When sapid matters, drinks
and fluid or loose particles of food, touch the taste-cells, they
excite the fine terminal branchlets of the gustatory nerve which enters
the cells. As we find that there are similar structures in most of the
higher animals, and that they also choose their food with some care,
we may confidently assume that they have sensations of taste like man.
However, no trace of this is found in many of the lower animals; in
these cases it is impossible to lay down a line of demarcation between
taste and smell.
In man and the higher air-breathing vertebrates the seat of the sense
of smell is in the nostrils; in man it is especially that part of the
mucous lining of the nasal cavity which we call the "olfactory region"
(the uppermost part of the nasal dividing wall, the superior and middle
meatus). It is necessary for a sensation of smell that the odorous
matter, or olfactory stimuli, be brought in a finely divided condition
over the moist olfactory membranes. When they touch the olfactory
cells--slender, rod-shaped cells with very fine hairs at the free
end--they excite the ends of the olfactory nerve which are connected
with the cells.
In many animals, especially mammals, the sense of smell has a much more
important part in life than it has in man, in whom it is relatively
feeble. It is well known that dogs and other carnivora, and even
ungulates, have a much keener smell. In these cases the nasal cavity,
which is the seat of the sense, is much larger, and the muscles in it
are much stronger. The nostrils of the air-breathing vertebrates have
been developed from a pair of open nasal depressions in the skin of
the fish's head. But in these aquatic vertebrates the chemical action
of the olfactory stimuli must be of a different character, like the
sensation of taste. The odorous matter is, in these cases, brought
into contact with the olfactory membrane in a liquid form (in which
condition it is not perceptible to man). In fact, the division between
the senses of smell and taste disappears altogether in the lower
animals. These two "chemical senses" are closely related, and have a
common feature in the direct chemical action of the stimulus on the
sensitive part of the skin.
A chemical sensation of matter that corresponds completely to the real
taste-sensation in the higher animals is found in some of the higher
carnivorous plants. The leaves of the sun-dew (_drosera rotundifolia_)
are very sensitive insect-traps, and are armed at the edge with
knob-like tentacles, sticky hairs that secrete an acid, flesh-digesting
juice. When a solid body (but not a raindrop) touches the surface of
the leaf the stimulus acts in such a way on the tentacle heads as to
contract the leaf. But the acid fluid which serves for digestion,
and corresponds to the gastric juice in the animal, is only secreted
by the corpuscles if the solid foreign body is nitrogenous (flesh or
cheese). Hence the leaves of these insectivorous plants taste their
meat diet, and distinguish it from other solids, to which they are
indifferent. In the broader sense, in fact, we may describe the points
of the roots of plants as organs of taste; they plunge into the richer
parts of the earth which yield more nourishment, and avoid the poor
parts. In unicellular plants and animals the action of chemical stimuli
is especially conspicuous when it is one-sided, and provokes definite
movements in one particular direction (_chemotaxis_).
The movements of unicellular organisms that are provoked by chemical
stimuli and are known as chemotropism (more recently as chemotaxis) are
particularly interesting because they show the existence of a chemical
sensitiveness, somewhat resembling taste or smell, in the lowest
organisms, and even in the homogeneous plasm of the monera. Repeated
experiments of Wilhelm Engelmann, Max Verworn, and others, have shown
that many bacteria, diatomes, infusoria, rhizopods, and other protists,
have a similar sense of taste; they move towards certain acids (for
instance, a drop of malic acid) or a bubble of oxygen that lies on
one side of the drop of water in which the protists are under the
microscope. Many pathogenetic bacteria secrete poisonous substances
which are very injurious to the human frame. The active white
blood-cells, leucocytes, in the human blood have a special "taste" for
these bacteria-poisons, and concentrate in large quantities, by means
of their amœboid movements, at those parts of the body where they
are secreted. If the leucocytes prove the stronger in their struggle
with the bacteria, they destroy them, and in this way they act as
sanitary officers in keeping poisonous infection out of our organism.
But if the bacteria win the battle, they are transported into other
parts of the body by the leucocytes; they distinguish their plasm by
taste, and may cause a deadly infection.
We have a particularly interesting and important species of chemical
irritation in the mutual attraction of the two sex-cells, to which
I gave the name of chemotropism thirty years ago, and which I
described as the earliest phylogenetic source of sexual love (see the
_Anthropogeny_, chapters vii. and xxix.). The remarkable phenomena
of impregnation, the most important of all the processes of sexual
generation, consist in the coalescence of the female ovum and the
male sperm-cell. This could not take place if the two cells had not a
sensation of their respective chemical constitution and disposition
for union; they come together under this impulse. This sexual affinity
is found at the lowest stages of plant life, in the protophyta and
algæ. With these both cells--the smaller male microgameta and the
larger female macrogameta--are often mobile, and swim about in order
to effect a union. In the higher plants and animals only the small
male cell is mobile as a rule, and swims towards the large immobile
ovum in order to blend with it. The sensation that impels it is of a
chemical nature, allied to taste and smell. This has been proved by
the splendid experiments of Pfeffer, who showed that the male ciliated
cells of ferns are attracted by malic acid, and those of the mosses by
cane-sugar, just in the same way as by the exhalation from the female
ovum. Conception depends on exactly the same erotic chemotropism in the
fertilization of all the higher organisms.
Erotic chemotropism must be regarded as a general sense-function of the
sexual cells in all amphigonous organisms, but in the higher organisms
special forms of the sex-sense, connected with specific organs, are
developed; as the source of sexual love they play a most important
part in the life of many of the histona. In man and most of the higher
animals these feelings of love are associated with the highest features
of psychic life, and have led to the formation of some most remarkable
customs, instincts, and passions. Wilhelm Bölsche has given us an
admirable selection from this infinitely rich and attractive realm
in his famous _Life of Love in Nature_ (1903). It is well known that
this sexual sense as we have it in man has been developed from the
nearest related mammals, the apes. But while it offers a shameless and
repulsive spectacle in many of the apes, it has been greatly ennobled
and refined in man in the development of civilization. However, the
sexual sense-organs and their specific energy have remained the same.
In the vertebrates and the articulates and many other metazoa the
copulative organs are equipped with special cell-forms (voluptuous
particles), which are the seat of intensely pleasurable feelings (see
the _Anthropogeny_, chapter xxix., plate 30). The pubic hairs which
clothe the _mons Veneris_ are also delicate organs of the sex-sense,
and so are the tactile hairs about the mouth. In these cases the
correlation between the sensitive forms of energy in the copulative
organs and the psychic functions of the central nervous system has
been remarkably developed. Moreover, a large part of the rest of the
skin may co-operate as a secondary organ of the sex-sense, as is seen
in the effect of caressing, stroking, embracing, kissing, etc. Goethe,
at once the greatest lyric poet and the subtlest and profoundest
monistic philosopher of Germany, has given unrivalled expression to
this sensual, yet supersensual, basis of sexual love. Ontogeny teaches
unmistakably that its elementary organs, the epidermic cells, develop
entirely from the ectoderm.
By "organic sensations" modern physiology understands the perception
of certain internal bodily states, which are mostly brought about by
chemical stimuli (to a small extent by mechanical and other irritation)
in the organs themselves. As subjective feelings of the organism itself
these states are most aptly called "feelings"--the positive states,
pleasure, comfort, delight; the negative, discomfort, pain, etc.
These organic sensations (also called common sensations or feelings)
are of great importance for the self-regulation of the complicated
organism. To the positive organic sensations belong not only the bodily
feeling of satiety, repose, or comfort, but also the psychic feelings
of joy, good humor, mental rest, etc. Among negative common feelings
we have not only hunger and thirst, bodily fatigue, bodily pain,
sea-sickness, etc., but also mental strain, vertigo, bad humor, and
so on. Between the two groups we have the third category of neutral
organic sensations, which involve neither pleasure nor pain, but merely
the perception of certain internal conditions, such as muscular strain
(in lifting heavy objects), the disposal of the limbs (in crossing the
legs), and so on.
Chemical sensation is just as general and important in organic nature
as in the life of organisms. In this case it is nothing less than the
basis of chemical affinity. No chemical process can be thoroughly
understood unless we attribute a mutual sensation to the atoms,
and explain their combination as due to a feeling of pleasure and
their separation to a feeling of displeasure. The great Empedocles
(fifth century B.C.) explained the origin of all things long ago by
the various combination of pure elements, the interaction of love
(attraction) and hate (repulsion). This attraction or repulsion is, of
course, unconscious, just as in the instincts of plants and animals. If
one prefers to avoid the term "sensation," it may be called "feeling"
(_æsthesis_), while the (involuntary) movement it provokes may be
called "inclination" (_tropesis_), and the capacity for the latter
"tropism" (more recently _taxis_, _cf._ chapter xii. of the _Riddle_).
We may illustrate it from the simplest case of chemical combination.
When we rub together sulphur and mercury, two totally different
elements, the atoms of the finely divided matter combine and form a
third and different chemical body, cinnabar. How would this simple
synthesis be possible unless the two elements _feel_ each other, move
towards each other, and _then_ unite?
We find universally distributed in nature the sensation of the
mechanical stimulus of gravitation, the most comprehensive statement
of which is given in Newton's law of gravity. According to this
fundamental and all-ruling law, any two particles of matter are
attracted in direct proportion to their mass and inverse proportion to
the square of their distance. This form of attraction, also, can be
traced to a "sensation of matter" in the mutually attracting atoms.
The local sensation that any body provokes by contact with the surface
of an organism is felt as pressure (_baros_). A stimulus that causes
this pressure alone brings about a counter-pressure as a reaction,
and an effort to neutralize it, the pressure-movement (_barotaxis_
or _barotropism_). Sensitiveness to pressure or the contact of solid
bodies is found throughout the organic world; it can be proved
experimentally among the protists as well as the histona. Special
sense-organs have been developed in the skin of the higher animals as
the instruments of this pressure-sense (baræsthesis) in the form of
tactile corpuscles; they are most numerous at the finger-tips and other
particularly sensitive parts. In many of the higher animals there is
a fine sense of touch in the feelers or tentacles, or (in the higher
articulates) in the horns or antennæ. Moreover, these tactile and
prehensile organs are also very widely found among the higher plants,
especially the climbing plants (vines, bryony, etc.). Their slender
creepers, which roll out spirally, have a very delicate feeling
for the nature of the supports which they embrace; they distinguish
between smooth and rough, thick and thin supports, and prefer the
latter. Many of the higher plants, which are particularly sensitive to
pressure, have, to an extent, special organs of touch (tentacles), and
reveal this by the movements of their leaves (the sensitive plants,
_mimosa_, _dionæa_, _oxalis_). But even among the unicellular protists
we find that the contact of solid bodies has an irritating effect, the
perception of which provokes corresponding movements (_thigmotaxis_ or
_thigmotropismus_). A peculiar form of pressure-sensation is produced
in many organisms by the flow of liquids; in the mycetozoa, for
instance, it provokes counter-movements (_rheotaxis_, _rheotropismus_),
as Ernst Strahl showed by his experiments on _æthelium septicum_.
We have an interesting analogy to the thigmotaxis of the viscous living
plasm in the elasticity of solid inorganic bodies, such as an elastic
steel-rod. In virtue of its springy nature, the elastic rod reacts
on the pressure of force that has bent it, and endeavors to regain
its former position. The spiral spring sets the works of the clock in
motion in virtue of its elasticity.
A very important part is played in botany by the action of gravitation
on the growth of plants. The attraction towards the centre of the earth
causes the positively geotropic roots to grow vertically into the
earth, while the negatively geotropic stalk pushes out in the opposite
direction. This applies also to a number of stationary animals which
are attached to the ground by roots, such as polyps, corals, bryozoa,
etc. And even the locomotion of free animals, the disposition of
their bodies to the ground, the position and posture of their limbs,
etc., is determined partly by the feeling of gravitation, and partly
by adaptation to certain functions which resist this, as in running,
swimming, and so on. All these geotropic sensations belong to the
same group of barotactile phenomena, as the fall of a stone or any
other effect of gravitation that depends on an inorganic feeling of
attraction.
As a result of these adaptations, we find a distinct sense of space
developed in the higher, free-moving animals. The feeling of the three
dimensions of space becomes an important means of orientation, and in
the vertebrates, from the fishes up to man, the three spiral canals
in the inner ear are developed as special organs of this. These three
semicircular canals, which lie vertically to each other in the three
dimensions of space, are the organs of the sensation that guides the
movements of the head, and, in relation to this, for the normal posture
of the body and the feeling of equilibrium. If the three spiral canals
are destroyed, the equilibrium is lost; the body totters and falls.
Hence, these organs are not of an acoustic, but a static or geotactic
character; and the same may be said of the so-called "auditory
vesicles" of many of the lower animals--round vesicles which contain
a liquid and a solid body, the otolith. When this body changes its
position with the change of posture of the whole frame, it presses on
the fine auditory hairs, or delicate terminations of the auscultory
nerve, which enters the vesicle. In fact, the sense of equilibrium is
often combined with the sense of hearing.
The perception of noises and tones, which we call hearing, is
restricted to a section of the higher, free-moving animals; if, that is
to say, the above-mentioned "auditory vesicles" in the lower animals
do not have acoustic as well as static sensations. The specific
sensation of hearing is due to vibration of the medium in which the
animal lives (air or water), or to vibrations of solid bodies (such as
tuning-forks) which are brought into touch with them. If the vibrations
are irregular, they are felt as "noises"; if regular, they are heard
as "tones" or notes; when a number of tones together (fundamental
and over-tones) excite a complex sensation, we have "timbre." The
vibrations of the sounding body are borne to the auditory cells, which
represent the terminal extensions of the auscultory nerve. The specific
sensation of hearing can, therefore, be traced originally to the sense
of pressure, from which it has been evolved. As the organ of hearing
is, like the eye, one of the principal instruments of the higher mental
life, and as the refined musical hearing of civilized man is often
taken to be a metaphysical power of the soul, it is important to note
that here again the starting-point was purely physical--that is to say,
it can be traced to the sense of pressure of matter, or gravitation.
The great importance of electricity as an agency in nature, both
organic and inorganic, has only lately been fully appreciated. Electric
changes are connected with many (if not, as is now supposed, with
all) chemical and optical processes. Man himself and most of the
higher animals have no electric organs (apart from the eye), and no
sense-organs that experience a specific electric sensation. It is
probably otherwise with many of the lower animals, especially those
that develop free electricity, such as the electric fishes. The larvæ
of frogs and embryos of fishes, if put in a vessel of water through
which a galvanic current is sent, place themselves when it is closed
with their longitudinal axis in the direction of the current, with
the head directed to the anode and the tail to the cathode (Hermann).
Again, the luminous sea-animals which cause the beautiful phenomenon
of the illumination of the sea, and the glow-worms and other luminous
organisms, have probably an unconscious feeling of the flow of electric
energy associated with these phenomena. Many plants show a direct
reaction to electric stimuli; when, for instance, we send a constant
galvanic current for some time through the points of their roots (very
sensitive organs, compared by Darwin to the brain of the animal), they
bend towards the cathode.
Many of the protists are very sensitive to electric currents, as Max
Verworn especially proved by a series of beautiful experiments. Most
of the ciliated infusoria and many of the rhizopods (_amœba_) are
cathodically sensitive or negatively galvanotactic. When we send a
constant electric current through a drop of water in which thousands of
_paramœcium_ are moving about, all the infusoria swim at once, with
the anterior pole of the body foremost, towards the cathode or negative
pole; they accumulate about it in great crowds. If the direction of the
current is now changed, the whole swarm at once make in the opposite
direction for the new cathode. Most of the flagellate infusoria do just
the reverse; they are anodically sensitive or positively galvanotactic.
In a drop of water, in which swarms of _polytoma_ are moving about,
all the cells swim at once towards the anode or positive pole, when an
electric current is sent through. The opposite galvanotropic behavior
of these two groups of infusoria in a drop of water, in which they
are mixed together, is very interesting; as soon as a constant stream
enters it, the ciliata fly to the cathode and the flagellata to the
anode. When the current is reversed the two swarms rush at each other
like hostile armies, cross in the middle of the drop, and gather at the
opposite poles. These and other phenomena of galvanic sensation show
clearly that the living plasm is subject to the same physical laws as
the water that is decomposed into hydrogen and oxygen by an electric
current. Both elements _feel_ the opposite electricities.
SCALE OF SENSATION AND IRRITABILITY
1st Stage: SENSATION OF ATOMS. Affinity of the elements in every
chemical combination.
2d Stage: SENSATION OF MOLECULES (groups of atoms): in the attraction
and repulsion of molecules (positive and negative electricity, etc.).
3d Stage: SENSATION OF PLASTIDULES (micella, biogens, or
plasma-molecules): in the simplest vital process of the monera
(chromacea and bacteria).
4th Stage: SENSATION OF CELLS: irritability of the unicellular
protists (protophyta and protozoa): erotic chemotropism connected
with the nucleus and trophic with the cell-body.
5th Stage: SENSATION OF CŒNOBIA (volvox, magosphæra). With the
formation of cell-communities we have association of sensations
(individual feeling on the part of the social cells together with
common feeling on the part of the community).
6th Stage: SENSATION OF THE LOWER PLANTS. In the metaphyta or
tissue-plants all the cells are still equally sensitive at the lower
stages: there are no special sense-organs.
7th Stage: SENSATION OF THE HIGHER PLANTS. In the higher metaphyta
specially sensitive cells, or groups of cells, with a specific
energy, are developed at certain points: sense-organs.
8th Stage: SENSATION OF THE LOWER METAZOA, without differentiated
nerves or sense-organs. Lower cœlenteria: sponges, polyps,
platodaria.
9th Stage: SENSATION OF THE HIGHER METAZOA, with differentiated
nerves and sense-organs, but still without consciousness(?). The
higher cœlenteria and most of the cœlomaria.
10th Stage: SENSATION WITH DAWNING CONSCIOUSNESS, with independent
formation of the phronema. The higher articulata (spiders and
insects) and vertebrates (amphibia, lower reptiles, lower mammals).
11th Stage: SENSATION WITH CONSCIOUSNESS AND THOUGHT: amniotes:
higher reptiles, birds, and mammals: savages.
12th Stage: SENSATION WITH PRODUCTIVE MENTAL ACTION IN ART AND
SCIENCE: civilized men.
XIV
MENTAL LIFE
Mind and soul--Intelligence and reason--Pure reason--Kant's
dualism--Anthropology--Anthropogeny--Embryology of the mind--Mind of
the embryo--The canonical mind--Legal rights of the embryo--Phylogeny
of the mind--Paleontology of the mind--Psyche and phronema--Mental
energy--Diseases of the mind--Mental powers--Conscious and
unconscious mental life--Monistic and dualistic theory--Mental life
of the mammals, of savages, and of civilized and educated people.
The greatest and most commanding of all the wonders of life is
unquestionably the mind of man. That function of the human organism,
to which we give the name of "mind," is not only the chief source of
all the higher enjoyment of life for ourselves, but it is also the
power that most effectually separates man from the brute according
to conventional beliefs. Hence it is supremely important for our
biological philosophy to devote a few careful pages to the study of its
nature, its origin and development, and its relation to the body.
At the very outset of our psychological inquiry we are met by the
difficulty of giving a clear definition of "mind," and distinguishing
it from "soul." Both ideas are extremely ambiguous: their content
and connotation are described in the most various ways by the
representatives of science. Generally speaking, we mean by mind that
part of the life of the soul which is connected with consciousness and
thought, and is, therefore, only found in the higher animals which have
intelligence and reason. In a narrower sense reason is regarded as the
proper function of mind, and as the essential prerogative of man in the
animal world. In this sense Kant especially has done much to strengthen
the prevailing conception of mental action, and has, by his _Critique
of Pure Reason_, converted philosophy into a mere "science of reason."
In consequence of this conception, which still prevails widely in
scientific circles, we will first study the mental life in the action
of reason, and try to form a clear idea of this great wonder of life.
Psychologists and metaphysicians are of very varied opinions as to
the difference between intelligence and reason. Schopenhauer, for
instance, considers causality to be the sole function of intelligence,
and the formation of concepts to be the province of reason; in his
opinion the latter power alone marks off man from the brute. However,
the power of abstraction, which collects the common features in a
number of different presentations, is also found in the higher animals.
Intelligent dogs not only discriminate between individual men, cats,
etc., according as they are sympathetic or the reverse, but they have
a general idea of man or cat, and behave very differently towards the
two. On the other hand, the power of forming concepts is still so
slight in uncivilized races that it rises but little above the mind of
dogs, horses, etc.; the mental interval between them and civilized man
is extremely wide. However, a long scale of reason unites the various
stages of association of presentations which lead up to the formation
of concepts; it is quite impossible to lay down a strict line of
demarcation between the lower and higher mental functions of animals,
or between the latter and reason. Hence the distinction between the
two cerebral functions is only relative; the intelligence comprises
the narrower circle of concrete and more proximate associations, while
reason deals with the wider sphere of abstract and more comprehensive
groups of association. In the scientific life of the mind, therefore,
the intelligence is always occupied with empirical investigation, and
reason with speculative knowledge. But the two faculties are equally
functions of the phronema, and depend on the normal anatomic and
chemical condition of this organ of thought.
Since Kant won so great a prominence in modern philosophy for the
idea of pure reason by his famous _Critique_ (1781), it has been much
discussed, especially in the modern metaphysical theory of knowledge.
It has, however, like all other ideas, undergone considerable changes
of meaning in the course of time. Kant himself at first understood
by pure reason "reason independent of all experience." But impartial
modern psychology based on the physiology of the brain and the
phylogeny of its functions, has shown that there is no such thing as
this pure _a priori_ knowledge, independent of all experience. Those
principles of reason which at present seem to be a priori in this sense
have been attained in virtue of thousands of experiences. In so far as
this is a question of real knowledge of the truth, Kant himself has
frequently recognized the point. He says expressly in his _Prolegomena
to any future metaphysic that can be regarded as Science_ (1783, p.
204): "A knowledge of things by pure reason or pure intelligence is
nothing but an empty appearance; only in experience is there truth."
In subscribing to this empirical theory of knowledge of Kant I. and
rejecting the transcendental theory of Kant II., we may on our side
understand by pure reason "knowledge without prejudices," free from all
dogma--all fictions of faith.
The familiar cry of modern metaphysicians, "Return to Kant," has become
so general in Germany that not only nearly all metaphysicians--the
official representatives of "philosophy" at our universities--but
also many distinguished scientists, regard Kant's dualistic theory of
knowledge as a necessary condition for the attainment of truth. Kant
dominated philosophy in the nineteenth century much as Aristotle did
in the Middle Ages. His authority became especially powerful when the
prevailing Christian faith believed that his "practical reason" fully
supported its own three fundamental dogmas--the personality of God, the
immortality of the soul, and the freedom of the will. It overlooked
the fact that Kant had utterly failed to find proofs of these dogmas
in his _Critique of Pure Reason_. Even conservative governments found
favorable features in this dualistic philosophy. We are, therefore,
forced to return once more to this mischievous system; though Kant's
antinomy of the two reasons has now been refuted so often and so
thoroughly that we need not dwell any further on this point.
Although the great Königsberg philosopher brought every side of
human life within his comprehensive sphere of study, man remained to
him--as he had been to Plato and Aristotle, Christ and Descartes--a
dual being, made up of a physical body and a transcendental mind or
spirit. Comparative anatomy and evolution, which have provided the
solid morphological basis of monistic anthropology, did not come
into existence until the beginning of the nineteenth century; they
were quite unknown to Kant. He had, however, a presentiment of their
importance, as Fritz Schultze has shown in his interesting work on
_Kant and Darwin_ (1875). We find in various places expressions which
may be described as anticipations of Darwinism. Kant also gave lectures
on "Pragmatic Anthropology," and studied the psychology of races and
peoples. It is remarkable that he did not arrive at a phylogenetic
conception of the human mind, and a recognition of the possibility of
its evolution from the mind of other vertebrates. It is clear that he
was held back from this by the profound mystic tendency of his theory
of reason, and the dogma of the immortality of the soul, the freedom
of the will, and the categorical imperative. Reason remained in Kant's
view a transcendental phenomenon, and this dualistic error had a
great influence on the whole structure of his philosophy. It must be
remembered, of course, that our knowledge of the psychology of peoples
was then very imperfect; but a critical study of the facts then known
should have sufficed to convince him of the lower and animal condition
of their minds. If Kant had had children, and followed patiently the
development of the child's soul (as Preyer did a century later), he
would hardly have persisted in his erroneous idea that reason, with
its power of attaining _a priori_ knowledge, is a transcendental and
supernatural wonder of life, or a unique gift to man from Heaven.
The root of the error is that Kant had no idea of the natural
evolution of the mind. He did not employ the comparative and genetic
methods to which we owe the chief scientific achievements of the last
half-century. Kant and his followers, who confined themselves almost
exclusively to the introspective method or the self-observation of
their own mind, regarded as the model of the human soul the highly
developed and versatile mind of the philosopher, and disregarded
altogether the lower stages of mental life which we find in the child
and the savage.
The immense advance made by the science of man in the second half
of the nineteenth century cut the ground from under the older
anthropology and the dualistic system of Kant. A number of newly
founded branches of science co-operated in the work. Comparative
anatomy showed that our whole complicated frame resembles that of
the other mammals, and in particular differs only by slight stages
of growth, and therefore in the details of the organs, from that
of the anthropoid apes. The comparative histology of the brain
especially showed that this is also true of the brain, the real organ
of mind. From comparative embryology we learned that man develops
from a simple ovum just like the anthropoid ape; in fact, that it is
almost impossible to distinguish between the ape and the human embryo
even at a late stage of development. Comparative animal chemistry
explained that the chemical compounds which build up our organs, and
the conversions of energy which accompany its metabolism, resemble
those in the other vertebrates. Comparative physiology taught us that
all man's vital functions--nutrition and reproduction, movement and
sensation--can be traced to the same physical laws in man as in all
the other vertebrates. Above all, the comparative and experimental
study of the sense-organs and the various parts of the brain showed
that these organs of the mind work in the same way in man as in the
other primates. Modern paleontology taught that man is, it is true,
more than a hundred thousand years old, but only appeared on earth
towards the close of the Tertiary Period. Prehistoric research and
comparative ethnology have shown that civilized nations were preceded
by older and lower races, and these by savages, which have a close
bodily and mental affinity to the apes. Finally, the reformed theory
of descent (1859) enabled us to unite the chief results of the various
branches of anthropological study, and explain them phylogenetically
by the development of man from other primates (anthropoid apes,
cynocephali, lemures, etc.). By this means a new and monistic basis
was provided for modern anthropology; the position assigned to man in
nature by dualistic metaphysics was shown to be utterly untenable. I
have attempted in the last edition of my _Anthropogeny_ (of which an
English edition is in preparation) to combine all these results of
empirical investigation in a sketch of the natural evolution of man,
paying special regard to embryology. I pointed out in chapters ii.-vi.
of the _Riddle_ how important a part of our monistic philosophy this
phylogenetic anthropology is.
The monistic conception of the human body and mind, which the theory
of descent has put on a zoological basis, was bound to meet with the
sternest resistance in dualistic and metaphysical circles. It was,
however, also regarded with great disapproval by many modern empirical
anthropologists, especially those who take it to be their chief
task to make as "exact" a study as possible of the human frame, and
measure and describe its various parts. We might have expected these
descriptive anthropologists and ethnologists to extend a friendly
hand to the new anthropogeny, and avail themselves of its leading
ideas, in order to bring unity and causal connection into the enormous
mass of empirical material accumulated. However, this took place
only to a limited extent, The majority of anthropologists regarded
evolution, and especially the evolution of man, as an undemonstrated
hypothesis. They confined themselves to accumulating huge masses of
raw empirical material, without having any clear aim or any definite
questions in view. This was chiefly the case in Germany, where the
Society of Anthropology and Prehistoric Research was for thirty years
under the lead of Rudolph Virchow. This famous scientist had won
great honor in connection with the reform of medicine by his cellular
pathology and a number of distinguished works on pathological anatomy
and histology since the middle of the nineteenth century. But when
he afterwards (subsequently to his removal to Berlin, 1856) devoted
himself chiefly to political and social questions, he lost sight of the
great advance made in other branches of biology. He completely failed
to appreciate its greatest achievement--the establishment of the
science of evolution by Darwin. To this we must add the psychological
metamorphosis (similar to that of Wundt, Baer, Dubois-Reymond, and
others), of which I have spoken in the sixth chapter of the _Riddle_.
The extraordinary authority of Virchow, and the indefatigable zeal
with which he struggled every year until his death (1903) against the
descent of man from other vertebrates, caused a wide-spread opposition
to the doctrine of evolution. This was supported especially by Johannes
Ranke, of Munich, the secretary of the Anthropological Society.
Happily, a change has recently set in. However, my _Anthropogeny_
has remained for thirty years the only work of its kind--namely, a
comprehensive treatment of man's ancestral history, especially in the
light of embryology.
As I pointed out in the eighth and ninth chapters of the _Riddle_, the
most solid foundation of our monistic psychology is the fact that the
human mind grows. Like every other function of our organism, our mental
activity exhibits the phenomenon of development in two directions,
individually in each human being and phyletically in the whole race.
The ontogeny of the mind--or the embryology of the human soul--brings
before us in direct observation the various stages of development
through which the mind of every man passes from the beginning to the
close of life. The phylogeny of the mind--or the ancestral history of
the human soul--does not afford us this direct observation; it can only
be deduced by a comparison and synthesis of the historical indications
which are supplied by history and prehistoric research on the one hand,
and the critical study of the various stages of mental life in savages
and the higher vertebrates on the other. In this the biogenetic law is
used with great success (chapter xvi.).
As everybody knows, the new-born child shows as yet no trace of mind
or reason or consciousness; these functions are wanting in it as
completely as in the embryo from which it has been developed during
the nine months in the mother's womb. Even in the ninth month, when
most of the organs of the human embryo are formed and arranged as they
appear later, there is no more trace of mind in its psychic life than
in the ovum and spermatozoon from which it was evolved. The moment in
which these sexual cells unite marks precisely the real commencement of
individual existence, and therefore of the soul also (as a potential
function of the plasm). But the mind proper--or reason, the higher
conscious function of the soul--only develops, slowly and gradually,
long after birth. As Flechsig has shown anatomically, the cortex in the
new-born child is not yet organized or capable of functioning. Rational
consciousness is even impossible for the child when it begins to speak;
it reveals itself for the first time (after the first year) at the
moment when the child speaks of itself, not in the-third person, but
as "I." With this self-consciousness comes also the antithesis of the
individual to the outer world, or world-consciousness. This is the real
beginning of mental life.
In defining the appearance of the individual mind by the awakening
of self-consciousness, we make it possible to distinguish, from the
monistic physiological point of view, between "soul" (_psyche_) and
"spirit" (_pneuma_). There is a soul even in the maternal ovum and
the paternal spermatozoon (_cf._ chapter xi.); there is an individual
soul in the stem-cell (_cytula_) which arises at conception by the
blending of the parent cells. But the mind proper, the thinking reason,
develops out of the animal intelligence (or earlier instincts) of the
child only with the consciousness of its personality as opposed to the
outer world. At the same time the child reaches the higher stage of
personality, which law has for a long time taken under its protection
and made morally responsible to society by education. This shows how
erroneous and untenable, from the physiological point of view, are the
ideas still embodied in our code as to the psychic life and the mind of
the embryo and the new-born infant. They came mostly from the canon law
of the Catholic Church.
The dualistic ideas of the soul of the human embryo which were taught
by the Church in the Middle Ages are particularly interesting from
the psychological point of view; and at the same time they are of
great practical importance even in our own day, since many of their
moral consequences form an important element in canon law, and have
passed from this into civil law. This influential canon law was formed
under ecclesiastical authority from the decisions of Church councils
and the decretals of the popes. It is, like most of the dogmas and
decrees which civilization owes to this powerful hierarchy, a curious
tissue of old traditions and new fictions, political dogmas, and
crass superstition. It is directed to the despotic ruling of the
uneducated masses and the exclusive dominion of the Church--a Church
that calls itself Christian while thus acting as the very reverse of
pure Christianity. The canon law takes its name from the dogmatic rules
(or canons) of the Church. They involuntarily suggest the metal tubes
which are so often the _ultima ratio regis_ in the wars of Christian
nations. The canonical regulations of the Church, as implements of a
crude spiritual despotism, have no more to do with the ethical laws
of pure reason than the cannons of secular authorities have as naked
organs of physical force. We might write the motto, _Ultima ratio
ecclesiæ_ (the last argument of the Church), over the sacred _Corpus
Juris Canonici_. A collection of later papal decretals which forms an
appendix to the books of canon law was very happily given the official
title of _Extravagantes_. Among the "extravagant" nonsense which the
papacy included in canon law as a moral code for believers is its view
of the psychic life of the embryo. The "immortal soul" is supposed
to enter the soulless embryo only several weeks after conception. As
theologians and metaphysicians are very much divided as to the period
of this entrance of the soul, and know nothing about the structure of
the embryo and its development, we will only recall the fact that the
human fœtus cannot be distinguished from that of the anthropoid
ape and other mammals even in the sixth week of its development. The
outline of the five cerebral vesicles and the three higher sense-organs
(nose, eye, and ear vesicle) is discernible in the head; the two
pairs of limbs can be traced in the shape of four simple roundish
unjointed plates; and the pointed tail sticks out at the lower part,
the rudimentary legacy from our long-tailed ape-ancestors. Although the
cortex is not yet developed at this stage, the embryo may be considered
to have a "soul" (_cf._ chapters xiv. and xv. of my _Anthropogeny_, and
plates 8-14).
It is said to be a great merit of canon law that it was the first to
extend legal protection to the human embryo, and punished abortion
with death as a mortal sin. But as this mystical theory of the
entrance of the soul is now scientifically untenable, we should expect
them consistently to extend this protection to the fœtus in its
earlier stages, if not to the ovum itself. The ovary of a mature maid
contains about 70,000 ova; each of these might be developed into a
human being under favorable circumstances if it united with a male
spermium after its release from the ovary. If the state is so eager
for the multiplication of its citizens in the general interest, and
regards prolific reproduction as a "duty" of its members, this is
certainly a "sin of omission." It punishes abortion with several
years' imprisonment. But while civil law thus takes its inspiration
from canon law, it overlooks the physiological fact that the ovum is
a part of the mother's body over which she has full right of control;
and that the embryo that develops from it, as well as the new-born
child, is quite unconscious, or is a purely "reflex machine," like
any other vertebrate. There is no mind in it as yet; it only appears
after the first year, when its organ, the phronema in the cortex, is
differentiated. This interesting fact is explained by the biogenetic
law, which shows that the ontogeny of the brain is a condensed
recapitulation of its phylogeny in virtue of the laws of heredity.