exclusively to human pathology for light. The existence of separate
speech and writing centres in the left hemisphere in man; the fact
that palsy from cortical injury is so much more complete and enduring
in man and the monkey than in dogs; and the farther fact that it seems
more difficult to get complete sensorial blindness from cortical
ablations in the lower animals than in man, all show that functions get
more specially localized as evolution goes on. In birds localization
seems hardly to exist, and in rodents it is much less conspicuous than
in carnivora. Even for man, however, Munk's way of mapping out the
cortex into absolute areas within which only one movement or sensation
is represented is surely false. The truth seems to be rather that,
although there is a correspondence of certain regions of the brain to
certain regions of the body, yet the several _parts_ within each bodily
region are represented throughout the _whole_ of the corresponding
brain-region like pepper and salt sprinkled from the same caster. This,
however, does not prevent each 'part' from having its _focus_ at one
spot within the brain-region. The various brain-regions merge into each
other in the same mixed way. As Mr. Horsley says: "There are border
centres, and the area of representation of the face merges into that
for the representation of the upper limb. If there was a focal lesion
at that point, you would have the movements of these two parts starting
together."[59] The accompanying figure from Paneth shows just how the
matter stands in the dog.[60]

[Illustration: FIG. 21.--Dog's motor centres, right hemisphere,
according to Paneth.--The points of the motor region are correlated as
follows with muscles: the _loops_ with the _orbicularis palpebrarum_;
the _plain crosses_ with the _flexor_, the _crosses inscribed in
circles_ with the _extensor, digitorum communis_ of the fore-paw;
the _plain circles_ with the _abductor pollicis longus_; the _double
crosses_ with the _extensor communis_ of the hind-limb.]

I am speaking now of localizations breadthwise over the brain-surface.
It is conceivable that there might be also localizations depthwise
through the cortex. The more superficial cells are smaller, the deepest
layer of them is large; and it has been suggested that the superficial
cells are sensorial, the deeper ones motor;[61] or that the superficial
ones in the motor region are correlated with the extremities of the
organs to be moved (fingers, etc.), the deeper ones with the more
central segments (wrist, elbow, etc.).[62] It need hardly be said that
all such theories are as yet but guesses.

We thus see that the postulate of Meynert and Jackson which we started
with on p. 30 is on the whole most satisfactorily corroborated by
subsequent objective research. _The highest centres do probably
contain nothing but arrangements for representing impressions and
movements, and other arrangements for coupling the activity Of these
arrangements together._[63] Currents pouring in from the sense-organs
first excite some arrangements, which in turn excite others, until
at last a motor discharge downwards of some sort occurs. When this is
once clearly grasped there remains little ground for keeping up that
old controversy about the motor zone, as to whether it is in reality
motor or sensitive. The whole cortex, inasmuch as currents run through
it, is both. All the currents probably have feelings going with them,
and sooner or later bring movements about. In one aspect, then,
every centre is afferent, in another efferent, even the motor cells
of the spinal cord having these two aspects inseparably conjoined.
Marique,[64] and Exner and Paneth[65] have shown that by cutting
_round_ a 'motor' centre and so separating it from the influence of
the rest of the cortex, the same disorders are produced as by cutting
it out, so that really it is only the mouth of the funnel, as it were,
through which the stream of innervation, starting from elsewhere,
pours;[66] consciousness accompanying the stream, and being mainly of
things seen if the stream is strongest occipitally, of things heard
if it is strongest temporally, of things felt, etc., if the stream
occupies most intensely the 'motor zone.' It seems to me that some
broad and vague formulation like this is as much as we can safely
venture on in the present state of science; and in subsequent chapters
I expect to give confirmatory reasons for my view.

MAN'S CONSCIOUSNESS LIMITED TO THE HEMISPHERES.

_But is the consciousness which accompanies the activity of the cortex
the only consciousness that man has?_ or _are his lower centres
conscious as well?_

This is a difficult question to decide, how difficult one only learns
when one discovers that the cortex-consciousness itself of certain
objects can be seemingly annihilated in any good hypnotic subject by a
bare wave of his operator's hand, and yet be proved by circumstantial
evidence to exist all the while in a split-off condition, quite as
'ejective'[67] to the rest of the subject's mind as that mind is to
the mind of the bystanders.[68] The lower centres themselves may
conceivably all the while have a split-off consciousness of their
own, similarly ejective to the cortex-consciousness; but whether
they have it or not can never be known from merely introspective
evidence. Meanwhile the fact that occipital destruction in man may
cause a blindness which is apparently absolute (no feeling remaining
either of light or dark over one half of the field of view), would
lead us to suppose that if our lower optical centres, the corpora
quadrigemina, and thalami, do have any consciousness, it is at all
events a consciousness which does not mix with that which accompanies
the cortical activities, and which has nothing to do with our personal
Self. In lower animals this may not be so much the case. The traces of
sight found (supra, p. 46) in dogs and monkeys whose occipital lobes
were entirely destroyed, may possibly have been due to the fact that
the lower centres of these animals saw, and that what they saw was
not ejective but objective to the remaining cortex, i.e. it formed
part of one and the same inner world with the things which that cortex
perceived. It may be, however, that the phenomena were due to the fact
that in these animals the cortical 'centres' for vision reach outside
of the occipital zone, and that destruction of the latter fails to
remove them as completely as in man. This, as we know, is the opinion
of the experimenters themselves. For practical purposes, nevertheless,
and limiting the meaning of the word consciousness to the personal
self of the individual, we can pretty confidently answer the question
prefixed to this paragraph by saying that _the cortex is the sole organ
of consciousness in man_.[69] If there be any consciousness pertaining
to the lower centres, it is a consciousness of which the self knows
nothing.

THE RESTITUTION OF FUNCTION.

Another problem, not so metaphysical, remains. The most general
and striking fact connected with cortical injury is that of the
_restoration of function_. Functions lost at first are after a few days
or weeks restored. _How are we to understand this restitution?_

Two theories are in the field:

1) Restitution is due to the vicarious action either of the rest of the
cortex or of centres lower down, acquiring functions which until then
they had not performed;

2) It is due to the remaining centres (whether cortical or 'lower')
resuming functions which they had always had, but of which the wound
had temporarily inhibited the exercise. This is the view of which Goltz
and Brown-Séquard are the most distinguished defenders.

Inhibition is a _vera causa_, of that there can be no doubt. The
pneumogastric nerve inhibits the heart, the splanchnic inhibits the
intestinal movements, and the superior laryngeal those of inspiration.
The nerve-irritations which may inhibit the contraction of arterioles
are innumerable, and reflex actions are often repressed by the
simultaneous excitement of other sensory nerves. For all such facts the
reader must consult the treatises on physiology. What concerns us here
is the inhibition exerted by different parts of the nerve-centres, when
irritated, on the activity of distant parts. The flaccidity of a frog
from 'shock,' for a minute or so after his medulla oblongata is cut, is
an inhibition from the seat of injury which quickly passes away.

What is known as 'surgical shock '(unconsciousness, pallor, dilatation
of splanchnic blood-vessels, and general syncope and collapse) in
the human subject is an inhibition which lasts a longer time. Goltz,
Freusberg, and others, cutting the spinal cord in dogs, proved that
there were functions inhibited still longer by the wound, but which
re-established themselves ultimately if the animal was kept alive.
The lumbar region of the cord was thus found to contain independent
vaso-motor centres, centres for erection, for control of the
sphincters, etc., which could be excited to activity by tactile stimuli
and as readily reinhibited by others simultaneously applied.[70]
We may therefore plausibly suppose that the rapid reappearance of
motility, vision, etc., after their first disappearance in consequence
of a cortical mutilation, is due to the passing off of inhibitions
exerted by the irritated surface of the wound. The only question is
whether _all_ restorations of function must be explained in this
one simple way, or whether some part of them may not be owing to
the formation of entirely new paths in the remaining centres, by
which they become 'educated' to duties which they did not originally
possess. In favor of an indefinite extension of the inhibition theory
facts may be cited such as the following: In dogs whose disturbances
due to cortical lesion have disappeared, they may in consequence of
some inner or outer accident reappear in all their intensity for 24
hours or so and then disappear again.[71] In a dog made half blind
by an operation, and then shut up in the dark, vision comes back
just as quickly as in other similar dogs whose sight is exercised
systematically every day.[72] A dog which has learned to beg before
the operation recommences this practice quite _spontaneously_ a week
after a double-sided ablation of the motor zone.[73] Occasionally,
in a pigeon (or even, it is said, in a dog) we see the disturbances
less marked immediately after the operation than they are half an hour
later.[74] This would be impossible were they due to the subtraction of
the organs which normally carried them on. Moreover the entire drift of
recent physiological and pathological speculation is towards enthroning
inhibition as an ever-present and indispensable condition of orderly
activity. We shall see how great is its importance, in the chapter on
the Will. Mr. Charles Mercier considers that no muscular contraction,
once begun, would ever stop without it, short of exhaustion of the
system;[75] and Brown-Séquard has for years been accumulating examples
to show how far its influence extends.[76] Under these circumstances it
seems as if error might more probably lie in curtailing its sphere too
much than in stretching it too far as an explanation of the phenomena
following cortical lesion.[77]

On the other hand, if we admit _no_ re-education of centres, we
not only fly in the face of an _a priori_ probability, but we find
ourselves compelled by facts to suppose an almost incredible number of
functions natively lodged in the centres below the _thalami_ or even in
those below the _corpora quadrigemina_. I will consider the _a priori_
objection after first taking a look at the facts which I have in mind.
They confront us the moment we ask ourselves just _which are the parts
which perform the functions abolished by an operation after sufficient
time has elapsed for restoration to occur?_

The first observers thought that they must be the _corresponding parts
of the opposite or intact hemisphere_. But as long ago as 1875 Carville
and Duret tested this by cutting out the fore-leg-centre on one side,
in a dog, and then, after waiting till restitution had occurred,
cutting it out on the opposite side as well. Goltz and others have
done the same thing.[78] If the opposite side were really the seat of
the restored function, the original palsy should have appeared again
and been permanent. But it did not appear at all; there appeared only
a palsy of the hitherto unaffected side. The next supposition is that
_the parts surrounding the cut-out region_ learn vicariously to perform
its duties. But here, again, experiment seems to upset the hypothesis,
so far as the motor zone goes at least; for we may wait till motility
has returned in the affected limb, and then both irritate the cortex
surrounding the wound without exciting the limb to movement, and ablate
it, without bringing back the vanished palsy.[79] It would accordingly
seem that _the cerebral centres below the cortex_ must be the seat
of the regained activities. But Goltz destroyed a dog's entire left
hemisphere, together with the _corpus striatum_ and the _thalamus_
on that side, and kept him alive until a surprisingly small amount
of motor and tactile disturbance remained.[80] These centres cannot
here have accounted for the restitution. He has even, as it would
appear,[81] ablated both the hemispheres of a dog, and kept him alive
51 days, able to walk and stand. The corpora striata and thalami in
this dog were also practically gone. In view of such results we seem
driven, with M. François-Franck,[82] to fall back on the _ganglia lower
still_, or even on the _spinal cord_ as the 'vicarious' organ of which
we are in quest. If the abeyance of function between the operation
and the restoration was due _exclusively_ to inhibition, then we must
suppose these lowest centres to be in reality extremely accomplished
organs. They must always have done what we now find them doing after
function is restored, even when the hemispheres were intact. Of course
this is conceivably the case; yet it does not seem very plausible. And
the _a priori_ considerations which a moment since I said I should
urge, make it less plausible still.

For, in the first place, the brain is essentially a place of currents,
which run in organized paths. Loss of function can only mean one of
two things, either that a current can no longer run in, or that if it
runs in, it can no longer run out, by its old path. Either of these
inabilities may come from a local ablation; and 'restitution' can then
only mean that, in spite of a temporary block, an inrunning current has
at last become enabled to flow out by its old path again--e.g., the
sound of 'give your paw' discharges after some weeks into the same
canine muscles into which it used to discharge before the operation. As
far as the cortex itself goes, since one of the purposes for which it
actually exists is the production of new paths,[83] the only question
before us is: Is the formation of _these particular 'vicarious'
paths_ too much to expect of its plastic powers? It would certainly
be too much to expect that a hemisphere should receive currents
from optic fibres whose _arriving-place_ within it is destroyed,
or that it should discharge into fibres of the pyramidal strand if
their _place of exit_ is broken down. Such lesions as these must be
irreparable _within that hemisphere_. Yet even then, through the other
hemisphere, the _corpus callosum_, and the bilateral connections in
the spinal cord, one can imagine some road by which the old muscles
might eventually be innervated by the same incoming currents which
innervated them before the block. And for all minor interruptions,
not involving the arriving-place of the 'cortico-petal' or the place
of exit of the 'cortico-fugal' fibres, roundabout paths of some sort
through the affected hemisphere itself must exist, for every point
of it is, remotely at least, in potential communication with every
other point. The normal paths are only paths of least resistance. If
they get blocked or cut, paths formerly more resistant become the
least resistant paths under the changed conditions. It must never be
forgotten that a current that runs in has got to run out _somewhere_;
and if it only once succeeds by accident in striking into its old place
of exit again, the thrill of satisfaction which the consciousness
connected with the whole residual brain then receives will reinforce
and fix the paths of that moment and make them more likely to be struck
into again. The resultant feeling that the old habitual act is at last
successfully back again, becomes itself a new stimulus which stamps all
the existing currents in. It is matter of experience that such feelings
of successful achievement do tend to fix in our memory whatever
processes have led to them; and we shall have a good deal more to say
upon the subject when we come to the Chapter on the Will.

My conclusion then is this: that some of the restitution of function
(especially where the cortical lesion is not too great) is probably due
to genuinely vicarious function on the part of the centres that remain;
whilst some of it is due to the passing off of inhibitions. In other
words, both the vicarious theory and the inhibition theory are true in
their measure. But as for determining that measure, or saying which
centres are vicarious, and to what extent they can learn new tricks,
that is impossible at present.

FINAL CORRECTION OF THE MEYNERT SCHEME.

And now, after learning all these facts, what are we to think of the
child and the candle-flame, and of that scheme which provisionally
imposed itself on our acceptance after surveying the actions of the
frog? (_Cf_. pp. 25-6, _supra_.) It will be remembered that we then
considered the lower centres _en masse_ as machines for responding to
present sense-impressions exclusively, and the hemispheres as equally
exclusive organs of action from inward considerations or ideas; and
that, following Meynert, we supposed the hemispheres to have no native
tendencies to determinate activity, but to be merely superadded organs
for breaking up the various reflexes performed by the lower centres,
and combining their motor and sensory elements in novel ways. It will
also be remembered that I prophesied that we should be obliged to
soften down the sharpness of this distinction after we had completed
our survey of the farther facts. The time has now come for that
correction to be made.

Wider and completer observations show us both that the lower centres
are more spontaneous, and that the hemispheres are more automatic,
than the Meynert scheme allows. Schrader's observations in Goltz's
Laboratory on hemisphereless frogs[84] and pigeons[85] give an
idea quite different from the picture of these creatures which is
classically current. Steiner's[86] observations on frogs already
went a good way in the same direction, showing, for example, that
locomotion is a well-developed function of the medulla oblongata. But
Schrader, by great care in the operation, and by keeping the frogs
a long time alive, found that at least in some of them the spinal
cord would produce movements of locomotion when the frog was smartly
roused by a poke, and that swimming and croaking could sometimes be
performed when nothing above the medulla oblongata remained.[87]
Schrader's hemisphereless frogs moved spontaneously, ate flies, buried
themselves in the ground, and in short did many things which before
his observations were supposed to be impossible unless the hemispheres
remained. Steiner[88] and Vulpian have remarked an even greater
vivacity in fishes deprived of their hemispheres. Vulpian says of his
brainless carps[89] that three days after the operation one of them
darted at food and at a knot tied on the end of a string, holding
the latter so tight between his jaws that his head was drawn out of
water. Later, "they see morsels of white of egg; the moment these
sink through the water in front of them, they follow and seize them,
sometimes after they are on the bottom, sometimes before they have
reached it. In capturing and swallowing this food they execute just the
same movements as the intact carps which are in the same aquarium. The
only difference is that they seem to see them at less distance, seek
them with less impetuosity and less perseverance in all the points of
the bottom of the aquarium, but they struggle (so to speak) sometimes
with the sound carps to grasp the morsels. It is certain that they do
not confound these bits of white of egg with other white bodies, small
pebbles for example, which are at the bottom of the water. The same
carp which, three days after operation, seized the knot on a piece of
string, no longer snaps at it now, but if one brings it near her, she
draws away from it by swimming backwards before it comes into contact
with her mouth."[90] Already on pp. 9-10, as the reader may remember,
we instanced those adaptations of conduct to new conditions, on the
part of the frog's spinal cord and thalami, which led Pflüger and Lewes
on the one hand and Goltz on the other to locate in these organs an
intelligence akin to that of which the hemispheres are the seat.

When it comes to birds deprived of their hemispheres, the evidence
that some of their acts have conscious purpose behind them is quite
as persuasive. In pigeons Schrader found that the state of somnolence
lasted only three or four days, after which time the birds began
indefatigably to walk about the room. They climbed out of boxes in
which they were put, jumped over or flew up upon obstacles, and their
sight was so perfect that neither in walking nor flying did they
ever strike any object in the room. They had also definite ends or
purposes, flying straight for more convenient perching places when
made uncomfortable by movements imparted to those on which they stood;
and of several possible perches they always chose the most convenient.
"If we give the dove the choice of a horizontal bar (_Reck_) or an
equally distant table to fly to, she always gives decided preference to
the table. Indeed she chooses the table even if it is several meters
farther off than the bar or the chair." Placed on the back of a chair,
she flies first to the seat and then to the floor, and in general
"will forsake a high position, although it give her sufficiently
firm support, and in order to reach the ground will make use of the
environing objects as intermediate goals of flight, showing a perfectly
correct judgment of their distance. Although able to fly directly to
the ground, she prefers to make the journey in successive stages....
Once on the ground, she hardly ever rises spontaneously into the
air."[91]

Young rabbits deprived of their hemispheres will stand, run, start
at noises, avoid obstacles in their path, and give responsive cries
of suffering when hurt. Rats will do the same, and throw themselves
moreover into an attitude of defence. Dogs never survive such an
operation if performed at once. But Goltz's latest dog, mentioned
on p. 70, which is said to have been kept alive for fifty-one days
after both hemispheres had been removed by a series of ablations and
the corpora striata and thalami had softened away, shows how much the
mid-brain centres and the cord can do even in the canine species.
Taken together, the number of reactions shown to exist in the lower
centres by these observations make out a pretty good case for the
Meynert scheme, as applied to these lower animals. That scheme demands
hemispheres which shall be mere supplements or organs of repetition,
and in the light of these observations they obviously are so to a great
extent. But the Meynert scheme also demands that the reactions of the
lower centres shall all be _native_, and we are not absolutely sure
that some of those which we have been considering may not have been
acquired after the injury; and it furthermore demands that they should
be machine-like, whereas the expression of some of them makes us doubt
whether they may not be guided by an intelligence of low degree.

Even in the lower animals, then, there is reason to soften down that
opposition between the hemispheres and the lower centres which the
scheme demands. The hemispheres may, it is true, only supplement the
lower centres, but the latter resemble the former in nature and have
some small amount at least of 'spontaneity' and choice.

But when we come to monkeys and man the scheme well-nigh breaks down
altogether; for we find that the hemispheres do not simply repeat
voluntarily actions which the lower centres perform as machines.
There are many functions which the lower centres cannot by themselves
perform at all. When the motor cortex is injured in a man or a monkey
genuine paralysis ensues, which in man is incurable, and almost or
quite equally so in the ape. Dr. Seguin knew a man with hemi-blindness,
from cortical injury, which had persisted unaltered for twenty-three
years. 'Traumatic inhibition' cannot possibly account for this. The
blindness must have been an 'Ausfallserscheinung,' due to the loss
of vision's essential organ. It would seem, then, that in these
higher creatures the lower centres must be less adequate than they
are farther down in the zoological scale; and that even for certain
elementary combinations of movement and impression the co-operation
of the hemispheres is necessary from the start. Even in birds and dogs
the power of _eating properly_ is lost when the frontal lobes are cut
off.[92]

The plain truth is that neither in man nor beast are the hemispheres
the virgin organs which our scheme called them. So far from being
unorganized at birth, they must have native tendencies to reaction
of a determinate sort.[93] These are the tendencies which we know as
_emotions_ and _instincts_, and which we must study with some detail in
later chapters of this book. Both instincts and emotions are reactions
upon special sorts of objects of _perception_; they depend on the
hemispheres; and they are in the first instance reflex, that is, they
take place the first time the exciting object is met, are accompanied
by no forethought or deliberation, and are irresistible. But they are
modifiable to a certain extent by experience, and on later occasions
of meeting the exciting object, the instincts especially have less of
the blind impulsive character which they had at first. All this will be
explained at some length in Chapter XXIV. Meanwhile we can say that the
multiplicity of emotional and instinctive reactions in man, together
with his extensive associative power, permit of extensive recouplings
of the original sensory and motor partners. The _consequences_ of one
instinctive reaction often prove to be the inciters of an opposite
reaction, and being _suggested_ on later occasions by the original
object, may then suppress the first reaction altogether, just as in the
case of the child and the flame. For this education the hemispheres do
not need to be _tabulæ rasæ_ at first, as the Meynert scheme would
have them; and so far from their being educated by the lower centres
exclusively, they educate themselves.[94]

We have already noticed the absence of reactions from fear and hunger
in the ordinary brainless frog. Schrader gives a striking account of
the instinctless condition of his brainless pigeons, active as they
were in the way of locomotion and voice. "The hemisphereless animal
moves in a world of bodies which ... are all of equal value for him....
He is, to use Goltz's apt expression, _impersonal_.... Every object is
for him only a space-occupying mass, he turns out of his path for an
ordinary pigeon no otherwise than for a stone. He may try to climb over
both. All authors agree that they never found any difference, whether
it was an inanimate body, a cat, a dog, or a bird of prey which came
in their pigeon's way. The creature knows neither friends nor enemies,
in the thickest company it lives like a hermit. The languishing cooing
of the male awakens no more impression than the rattling of the peas,
or the call-whistle which in the days before the injury used to make
the birds hasten to be fed. Quite as little as the earlier observers
have I seen hemisphereless she-birds answer the courting of the male.
A hemisphereless male will coo all day long and show distinct signs
of sexual excitement, but his activity is without any object, it is
entirely indifferent to him whether the she-bird be there or not. If
one is placed near him, he leaves her unnoticed.... As the male pays
no attention to the female, so she pays none to her young. The brood
may follow the mother ceaselessly calling for food, but they might as
well ask it from a stone.... The hemisphereless sphereless pigeon is
in the highest degree tame, and fears man as little as cat or bird of
prey."[95]

Putting together now all the facts and reflections which we have been
through, it seems to me that _we can no longer hold strictly to the
Meynert scheme_. If anywhere, it will apply to the lowest animals;
but in them especially the lower centres seem to have a degree of
spontaneity and choice. On the whole, I think that we are driven to
substitute for it some such general conception as the following, which
allows for zoological differences as we know them, and is vague and
elastic enough to receive any number of future discoveries of detail.

CONCLUSION.

All the centres, in all animals, whilst they are in one aspect
mechanisms, probably are, or at least once were, organs of
consciousness in another, although the consciousness is doubtless
much more developed in the hemispheres than it is anywhere else. The
consciousness must everywhere _prefer_ some of the sensations which it
gets to others; and if it can remember these in their absence, however
dimly, they must be its _ends_ of desire. If, moreover, it can identify
in memory any motor discharges which may have led to such ends, and
associate the latter with them, then these motor discharges themselves
may in turn become desired as _means_. This is the development of
_will_; and its realization must of course be proportional to the
possible complication of the consciousness. Even the spinal cord
may possibly have some little power of will in this sense, and of
effort towards modified behavior in consequence of new experiences of
sensibility.[96]

All nervous centres have then in the first instance one essential
function, that of 'intelligent' action. They feel, prefer one thing to
another, and have 'ends.' Like all other organs, however, they _evolve_
from ancestor to descendant, and their evolution takes two directions,
the lower centres passing downwards into more unhesitating automatism,
and the higher ones upwards into larger intellectuality.[97] Thus it
may happen that those functions which can safely grow uniform and fatal
become least accompanied by mind, and that their organ, the spinal
cord, becomes a more and more soulless machine; whilst on the contrary
those functions which it benefits the animal to have adapted to
delicate environing variations pass more and more to the hemispheres,
whose anatomical structure and attendant consciousness grow more and
more elaborate as zoological evolution proceeds. In this way it might
come about that in man and the monkeys the basal ganglia should do
fewer things by themselves than they can do in dogs, fewer in dogs
than in rabbits, fewer in rabbits than in hawks,[98] fewer in hawks
than in pigeons, fewer in pigeons than in frogs, fewer in frogs than
in fishes, and that the hemispheres should correspondingly do more.
This passage of functions forward to the ever-enlarging hemispheres
would be itself one of the evolutive changes, to be explained like
the development of the hemispheres themselves, either by fortunate
variation or by inherited effects of use. The reflexes, on this view,
upon which the education of our human hemispheres depends, would not
be due to the basal ganglia alone. They would be tendencies in the
hemispheres themselves, modifiable by education, unlike the reflexes of
the medulla oblongata, pons, optic lobes and spinal cord. Such cerebral
reflexes, if they exist, form a basis quite as good as that which the
Meynert scheme offers, for the acquisition of memories and associations
which may later result in all sorts of 'changes of partners' in the
psychic world. The diagram of the baby and the candle (see page 25)
can be re-edited, if need be, as an entirely cortical transaction. The
original tendency to touch will be a cortical instinct; the burn will
leave an image in another part of the cortex, which, being recalled
by association, will inhibit the touching tendency the next time the
candle is perceived, and excite the tendency to withdraw--so that the
retinal picture will, upon that next time, be coupled with the original
motor partner of the pain. We thus get whatever psychological truth
the Meynert scheme possesses without entangling ourselves on a dubious
anatomy and physiology.

Some such shadowy view of the evolution of the centres, of the relation
of consciousness to them, and of the hemispheres to the other lobes,
is, it seems to me, that in which it is safest to indulge. If it has no
other advantage, it at any rate makes us realize how enormous are the
gaps in our knowledge, the moment we try to cover the facts by any one
formula of a general kind.

FOOTNOTES:

[4] It should be said that this particular cut commonly proves fatal.
The text refers to the rare cases which survive.

[5] I confine myself to the frog for simplicity's sake. In higher
animals, especially the ape and man, it would seem as if not only
determinate combinations of muscles, but limited groups or even single
muscles could be innervated from the hemispheres.

[6] I hope that the reader will take no umbrage at my so mixing the
physical and mental, and talking of reflex acts and hemispheres
and reminiscences in the same breath, as if they were homogeneous
quantities and factors of one causal chain. I have done so
deliberately; for although I admit that from the radically physical
point of view it is easy to conceive of the chain of events amongst
the cells and fibres as complete in itself, and that whilst so
conceiving it one need make no mention of 'ideas,' I yet suspect that
point of view of being an unreal abstraction. Reflexes in centres may
take place even where accompanying feelings or ideas guide them. In
another chapter I shall try to show reasons for not abandoning this
common-sense position; meanwhile language lends itself so much more
easily to the mixed way of describing, that I will continue to employ
the latter. The more radical-minded reader can always read 'ideational
process' for 'idea.'

[7] I shall call it hereafter for shortness 'the Meynert scheme;' for
the child-and-flame example, as well as the whole general notion that
the hemispheres are a supernumerary surface for the projection and
association of sensations and movements natively coupled in the centres
below, is due to Th. Meynert, the Austrian anatomist. For a popular
account of his views, see his pamphlet 'Zur Mechanik des Gehirnbaues,'
Vienna, 1874. His most recent development of them is embodied in
his 'Psychiatry,' a clinical treatise on diseases of the forebrain,
translated by B. Sachs, New York, 1885.

[8] Geschichte des Materialismus, 2d ed., ii, p. 345.

[9] West Riding Asylum Reports, 1876, p. 267.

[10] For a thorough discussion of the various objections, see Ferrier's
'Functions of the Brain,' 2d ed., pp. 227-234, and François-Franck's
'Leçons sur les Fonctions Motrices du Cerveau' (1887), Leçon 31. The
most minutely accurate experiments on irritation of cortical points are
those of Paneth, in Pflüger's Archiv, vol 37, p. 528.--Recently the
skull has been fearlessly opened by surgeons, and operations upon the
human brain performed, sometimes with the happiest results. In some
of these operations the cortex has been electrically excited for the
purpose of more exactly localizing the spot, and the movements first
observed in dogs and monkeys have then been verified in men.

[11] J. Loeb: Beiträge zur Physiologie des Grosshirns; Pflüger's
Archiv, xxxix, 293. I simplify the author's statement.

[12] Goltz: Pflüger's Archiv, xlii, 419.

[13] 'Hemiplegia' means one-sided palsy.

[14] Philosophical Transactions, vol. 179, pp. 6, 10 (1888). In a
later paper (_ibid._ p. 205) Messrs. Beevor and Horsley go into the
localization still more minutely, showing spots from which single
muscles or single digits can be made to contract.

[15] Nothnagel und Naunyn; Die Localization in den Gehirnkrankheiten
(Wiesbaden, 1887), p. 34.

[16] An accessible account of the history of our knowledge of motor
aphasia is in W. A. Hammond's 'Treatise on the Diseases of the Nervous
System,' chapter vii.

[17] The history up to 1885 may be found in A. Christiani: Zur
Physiologie des Gehirnes (Berlin, 1885).

[18] Pflüger's Archiv, vol. 44, p. 176. Munk (Berlin Academy
Sitzsungberichte, 1889, xxxi) returns to the charge, denying the
extirpations of Schrader to be complete: "Microscopic portions of the
_Sehsphäre_ must remain."

[19] A. Christiani; Zur Physiol. d. Gehirnes (Berlin, 1885), chaps. ii,
iii, iv, H. Munk: Berlin Akad. Stzgsb. 1884, xxiv.

[20] Luciani und Seppili: Die Functions-Localization auf der
Grosshirnrinde (Deutsch von Fraenkel), Leipzig, 1886, Dogs M, N, and
S. Goltz in Pflüger's Archiv, vol. 34, pp. 490-6; vol. 42, p. 454. Cf.
also Munk: Berlin Akad. Stzgsb. 1886, vii, viii, pp. 113-121, and Loeb:
Pflüger's Archiv, vol. 39, p. 337.

[21] Berlin Akad. Sitzungsberichte, 1886, vii, viii, p. 124.

[22] H. Munk: Functionen der Grosshirnrinde (Berlin, 1881), pp. 36-40.
Ferrier: Functions, etc., 2d ed., chap, ix, pt. i. Brown and Schaefer,
Philos. Transactions, vol. 179, p. 321. Luciani u. Seppili, op. cit.
pp. 131-138. Lannegrace found traces of sight with both occipital lobes
destroyed, and in one monkey even when angular gyri and occipital lobes
were destroyed altogether. His paper is in the Archives de Médecine
Expérimentale for January and March, 1889. I only know it from the
abstract in the Neurologisches Centralblatt, 1889, pp. 108-420. The
reporter doubts the evidence of vision in the monkey. It appears to
have consisted in avoiding obstacles and in emotional disturbance in
the presence of men.

[23] Localization of Cerebral Disease (1878), pp. 117-8.

[24] For cases see Flechsig: Die Leitungsbahnen in Gehirn u. Rückenmark
(Leipzig, 1876), pp. 112, 272; Exner's Untersuchungen, etc., p. 83;
Ferrier's Localization, etc., p. 11; François-Franck's Cerveau Moteur,
p. 63, note.

[25] E. C. Seguin: Hemianopsia of Cerebral Origin, in Journal of
Nervous and Mental Disease, vol. xiii, p. 30. Nothnagel und Naunyn:
Ueber die Localization der Gehirnkrankheiten (Wiesbaden, 1887), p. 16.

[26] Die Seelenblindheit, etc., p. 51 ff. The mental blindness was in
this woman's case moderate in degree.

[27] Archiv f. Psychiatrie, vol. 21, p. 222.

[28] Nothnagel (_loc. cit._ p. 22) says: "_Dies trifft aber nicht zu_."
He gives, however, no case in support of his opinion that double-sided
cortical lesion may make one stone-blind and yet not destroy one's
visual images; so that I do not know whether it is an observation of
fact or an _a priori_ assumption.

[29] In a case published by C. S. Freund: Archiv f. Psychiatrie,
vol. xx, the occipital lobes were injured, but their cortex was not
destroyed, on both sides. There was still vision. Cf. pp. 291-5.

[30] I say 'need,' for I do not of course deny the _possible_
coexistence of the two symptoms. Many a brain-lesion might block
optical associations and at the same time impair optical imagination,
without entirely stopping vision. Such a case seems to have been the
remarkable one from Charcot which I shall give rather fully in the
chapter on Imagination.

[31] Freund (in the article cited above 'Ueber optische Aphasie und
Seelenblindheit') and Bruns ('Ein Fall von Alexie,' etc., in the
Neurologisches Centralblatt for 1888, pp. 581, 509) explain their
cases by broken-down conduction. Wilbrand, whose painstaking monograph
on mental blindness was referred to a moment ago, gives none but _a
priori_ reasons for his belief that the optical 'Erinnerungsfeld' must
be locally distinct from the Wahrnehmungsfeld (cf. pp. 84, 93). The _a
priori_ reasons are really the other way. Mauthner ('Gehirn u. Auge'
(1881), p. 487 ff.) tries to show that the 'mental blindness' of Munk's
dogs and apes after occipital mutilation was not such, but real dimness
of sight. The best case of mental blindness yet reported is that by
Lissauer, as above. The reader will also do well to read Bernard: De
l'Aphasie (1885) chap. v; Ballet: Le Langage Intérieur (1886), chap.
viii; and Jas. Boss's little book on Aphasia (1887), p. 74.

[32] For a case see Wernicke's Lehrb. d. Gehirnkrankheiten, vol. ii, p.
554 (1881).

[33] The latest account of them is the paper 'Über die optischen
Centren u. Bahnen' by von Monakow in the Archiv für Psychiatrie, vol.
xx, p. 714.

[34] Die Functions-Localization, etc., Dog X; see also p. 161.

[35] Philos. Trans., vol. 179, p. 312.

[36] Brain, vol. xi, p. 10.

[37] _Ibid._ p. 147.

[38] Der aphasische Symptomencomplex (1874). See in Fig. 11 the
convolution marked WERNICKE.

[39] 'The Pathology of Sensory Aphasia,' 'Brain,' July, 1889.

[40] Nothnagel und Naunyn; _op. cit._ plates.

[41] Ballet's and Bernard's works cited on p. 51 are the most
accessible documents of Charcot's school. Bastian's book on the Brain
as an Organ of Mind (last three chapters) is also good.

[42] For details, see Ferrier's 'Functions,' chap. ix, pt. iii, and
Chas. K. Mills: Transactions of Congress of American Physicians and
Surgeons, 1888, vol. i, p. 278.

[43] Functions of the Brain, chap. x, § 14.

[44] Ueber die Functionen d. Grosshirnrinde (1881), p. 50.

[45] Lezioni di Fisiologia sperimentale sul sistema nervoso encefalico
(l. 73), p. 527 ff. Also 'Brain,' vol. ix, p. 298.

[46] Bechterew (Pflüger's Archiv, vol. 35, p. 137) found _no_
anæsthesia in a cat with motor symptoms from ablation of sigmoid gyrus.
Luciani got hyperæsthesia coexistent with cortical motor defect in a
dog, by simultaneously hemisecting the spinal cord (Luciani u. Seppili,
_op. cit._ p. 234). Goltz frequently found hyperæsthesia of the whole
body to accompany motor defect after ablation of both frontal lobes,
and he once found it after ablating the motor zone (Pflüger's Archiv,
vol. 34, p. 471).

[47] Philos. Transactions, vol. 179, p. 20 ff.

[48] Functions, p. 375.

[49] Pp. 15-17.

[50] Luciani u. Seppili, _op. cit._ pp. 275-288.

[51] _Op. cit._ p. 18.

[52] Trans. of Congress, etc., p. 272.

[53] See Exner's Unters. üb. Localization, plate xxv.

[54] Cf. Ferrier's Functions, etc., chap. iv, and chap. x, §§ 6 to 9.

[55] _Op. cit._ p. 17.

[56] E.g. Starr, _loc. cit._ p. 272; Leyden, Beiträge zur Lehre v. d.
Localization im Gehirn (1888), p. 72.

[57] Bernard, _op. cit._ p. 84.

[58] Philos. Trans., vol. 179, p. 3.

[59] Trans. of Congress of Am. Phys. and Surg. 1888, vol. i, p. 343.
Beevor and Horsley's paper on electric stimulation of the monkey's
brain is the most beautiful work yet done for precision. See Phil.
Trans., vol. 179, p. 205, especially the plates.

[60] Pflüger's Archiv, vol. 37, p. 523 (1885).

[61] By Luys in his generally preposterous book 'The Brain'; also by
Horsley.

[62] C. Mercier: The Nervous System and the Mind, p. 124.

[63] The frontal lobes as yet remain a puzzle. Wundt tries to explain
them as an organ of 'apperception' (Grundzüge d. Physiologischen
Psychologie, 3d ed., vol. i, p. 233 ff.), but I confess myself unable
to apprehend clearly the Wundtian philosophy so far as this word
enters into it, so must be contented with this bare reference.--Until
quite recently it was common to talk of an 'ideational centre' as of
something distinct from the aggregate of other centres. Fortunately
this custom is already on the wane.

[64] Rech. Exp. sur le Fonctionnement des Centres Psycho-moteurs
(Brussels, 1885).

[65] Pflüger's Archiv, vol. 44, p. 544.

[66] I ought to add, however, that François-Franck (Fonctions Motrices,
p. 370) got, in two dogs and a cat, a different result from this sort
of 'circumvallation.'

[67] For this word, see T. K. Clifford's Lectures and Essays (1879),
vol. ii, p. 72.

[68] See below, Chapter VIII.

[69] Cf. Ferrier's Functions, pp. 120, 147, 414. See also Vulpian:
Leçons sur la Physiol. du Syst. Nerveux, p. 548; Luciani u. Seppili,
_op. cit._ pp. 404-5; H. Maudsley: Physiology of Mind (1876), pp. 138
ff., 197 ff., and 241 ff. In G. H. Lewes's Physical Basis of Mind,
Problem IV: 'The Reflex Theory,' a very full history of the question is
given.

[70] Goltz: Pflüger's Archiv, vol. 8, p. 460; Freusberg: _ibid._ vol.
10, p. 174.

[71] Goltz: Verrichtungen des Grosshirns, p. 78.

[72] Loeb: Pflüger's Archiv, vol. 89, p. 276.

[73] _Ibid._ p. 289.

[74] Schrader: _ibid._ vol. 44, p. 218.

[75] The Nervous System and the Mind (1888), chaps. iii, vi; also in
Brain, vol. xi, p. 361.

[76] Brown-Séquard has given a resume of his opinions in the Archives
de Physiologie for Oct. 1889, 5me. Série, vol. i, p 751.

[77] Goltz first applied the inhibition theory to the brain in his
'Verrichtungen des Grosshirns,' p. 39 ff. On the general philosophy
of Inhibition the reader may consult Brunton's 'Pharmakology and
Therapeutics,' p. 154 ff., and also 'Nature,' vol. 27, p. 419 ff.

[78] E.g. Herzen, Herman u. Schwalbe's Jahres-bericht for 1886,
Physiol. Abth. p. 38. (Experiments on new-born puppies.)

[79] François-Franck: _op. cit._ p. 382. Results are somewhat
contradictory.

[80] Pflüger's Archiv, vol. 42, p. 419.

[81] Neurologisches Centralblatt, 1889, p. 372.

[82] _Op. cit._ p. 387. See pp. 378 to 388 for a discussion of the
whole question. Compare also Wundt's Physiol. Psych., 3d ed., i, 225
ff., and Luciani u. Seppili, pp. 243, 293.

[83] The Chapters on Habit, Association, Memory, and Perception will
change our present preliminary conjecture that that is one of its
essential uses, into an unshakable conviction.

[84] Pflüger's Archiv, vol. 41, p. 75 (1887).

[85] _Ibid._ vol. 44, p. 175 (1889).

[86] Untersuchungen über die Physiologie des Froschhirns. 1885.

[87] _Loc. cit._ pp. 80, 82-3. Schrader also found a _biting-reflex_
developed when the medulla oblongata is cut through just behind the
cerebellum.

[88] Berlin Akad. Sitzungsberichte for 1886.

[89] Comptes Rendus, vol. 102, p. 90.

[90] Comptes Rendus de l'Acad. d. Sciences, vol. 102, p. 1530.

[91] _Loc. cit._ p. 210.

[92] Goltz: Pflüger's Archiv, vol. 42, p. 447; Schrader: _ibid._ vol.
44, p. 219 ff. It is possible that this symptom may be an effect of
traumatic inhibition, however.

[93] A few years ago one of the strongest arguments for the theory that
the hemispheres are purely supernumerary was Soltmann's often-quoted
observation that in new-born puppies the motor zone of the cortex is
not excitable by electricity and only becomes so in the course of a
fortnight, presumably after the experiences of the lower centres have
educated it to motor duties. Paneth's later observations, however, seem
to show that Soltmann may have been misled through overnarcotizing his
victims (Pflüger's Archiv, vol. 37, p. 202). In the Neurologisches
Centralblatt for 1889, p. 513, Bechterew returns to the subject on
Soltmann's side without, however, noticing Paneth's work.

[94] Münsterberg (Die Willenshandlung, 1888, p. 134) challenges
Meynert's scheme _in toto_, saying that whilst we have in our personal
experience plenty of examples of acts which were at first voluntary
becoming secondarily automatic and reflex, we have no conscious
record of a single originally reflex act growing voluntary.--As far
as conscious record is concerned, we could not possibly have it even
if the Meynert scheme were wholly true, for the education of the
hemispheres which that scheme postulates must in the nature of things
antedate recollection. But it seems to me that Münsterberg's rejection
of the scheme may possibly be correct as regards reflexes from the
_lower centres_. Everywhere in this department of psychogenesis we are
made to feel how ignorant we really are.

[95] Pflüger's Archiv, vol. 44, p. 230-1.

[96] Naturally, as Schiff long ago pointed out (Lehrb. d. Muskel-u.
Nervenphysiologie, 1859, p. 213 ff.), the 'Rückenmarksseele,' if it
now exist, can have no higher sense-consciousness, for its incoming
currents are solely from the skin. But it may, in its dim way, both
feel, prefer, and desire. See, for the view favorable to the text:
G. H. Lewes, The Physiology of Common Life (1860), chap. ix. Goltz
(Nervencentren des Frosches 1869, pp. 102-130) thinks that the frog's
cord has no adaptative power. This may be the case in such experiments
as his, because the beheaded frog's short span of life does not give
it time to learn the new tricks asked for. But Rosenthal (Biologisches
Centralblatt, vol. iv, p. 247) and Mendelssohn (Berlin Akad.
Sitzungsberichte, 1885, p. 107) in their investigations on the simple
reflexes of the frog's cord, show that there is some adaptation to new
conditions, inasmuch as when usual paths of conduction are interrupted
by a cut, new paths are taken. According to Rosenthal, these grow more
pervious (i.e. require a smaller stimulus) in proportion as they are
more often traversed.

[97] Whether this evolution takes place through the inheritance of
habits acquired, or through the preservation of lucky variations, is an
alternative which we need not discuss here. We shall consider it in the
last chapter in the book. For our present purpose the _modus operandi_
of the evolution makes no difference, provided it be admitted to occur.

[98] See Schrader's Observations, _loc. cit._

CHAPTER III.

ON SOME GENERAL CONDITIONS OF BRAIN-ACTIVITY.

The elementary properties of nerve-tissue on which the brain-functions
depend are far from being satisfactorily made out. The scheme that
suggests itself in the first instance to the mind, because it is so
obvious, is certainly false: I mean the notion that each cell stands
for an idea or part of an idea, and that the ideas are associated or
'bound into bundles' (to use a phrase of Locke's) by the fibres. If we
make a symbolic diagram on a blackboard, of the laws of association
between ideas, we are inevitably led to draw circles, or closed figures
of some kind, and to connect them by lines. When we hear that the
nerve-centres contain cells which send off fibres, we say that Nature
has realized our diagram for us, and that the mechanical substratum
of thought is plain. In _some_ way, it is true, our diagram must be
realized in the brain; but surely in no such visible and palpable way
as we at first suppose.[99] An enormous number of the cellular bodies
in the hemispheres are fibreless. Where fibres are sent off they soon
divide into untraceable ramifications; and nowhere do we see a simple
coarse anatomical connection, like a line on the blackboard, between
two cells. Too much anatomy has been found to order for theoretic
purposes, even by the anatomists; and the popular-science notions of
cells and fibres are almost wholly wide of the truth. Let us therefore
relegate the subject of the _intimate_ workings of the brain to the
physiology of the future, save in respect to a few points of which a
word must now be said. And first of

THE SUMMATION OF STIMULI

in the same nerve-tract. This is a property extremely important for the
understanding of a great many phenomena of the neural, and consequently
of the mental, life; and it behooves us to gain a clear conception of
what it means before we proceed any farther.

The law is this, that _a stimulus which would be inadequate by itself
to excite a nerve-centre to effective discharge may, by acting with
one or more other stimuli (equally ineffectual by themselves alone)
bring the discharge about_. The natural way to consider this is as a
summation of tensions which at last overcome a resistance. The first of
them produce a 'latent excitement' or a 'heightened irritability'--the
phrase is immaterial so far as practical consequences go; the last is
the straw which breaks the camel's back. Where the neural process is
one that has consciousness for its accompaniment, the final explosion
would in all cases seem to involve a vivid state of feeling of a more
or less substantive kind. But there is no ground for supposing that
the tensions whilst yet submaximal or outwardly ineffective, may not
also have a share in determining the total consciousness present in the
individual at the time. In later chapters we shall see abundant reason
to suppose that they do have such a share, and that without their
contribution the fringe of relations which is at every moment a vital
ingredient of the mind's object, would not come to consciousness at all.

The subject belongs too much to physiology for the evidence to be cited
in detail in these pages. I will throw into a note a few references
for such readers as may be interested in following it out,[100] and
simply say that the direct electrical irritation of the cortical
centres sufficiently proves the point. For it was found by the earliest
experimenters here that whereas it takes an exceedingly strong current
to produce any movement when a single induction-shock is used, a rapid
succession of induction-shocks ('faradization') will produce movements
when the current is comparatively weak. A single quotation from an
excellent investigation will exhibit this law under further aspects:

 "If we continue to stimulate the cortex at short intervals with the
 strength of current which produces the minimal muscular contraction
 [of the dog's digital extensor muscle], the amount of contraction
 gradually increases till it reaches the maximum. Each earlier
 stimulation leaves thus an effect behind it, which increases the
 efficacy of the following one. In this summation of the stimuli....
 the following points may be noted: 1) Single stimuli entirely
 inefficacious when alone may become efficacious by sufficiently rapid
 reiteration. If the current used is very much less than that which
 provokes the first beginning of contraction, a very large number of
 successive shocks may be needed before the movement appears--20, 50,
 once 106 shocks were needed. 2) The summation takes place easily in
 proportion to the shortness of the interval between the stimuli. A
 current too weak to give effective summation when its shocks are
 3 seconds apart will be capable of so doing when the interval is
 shortened to 1 second. 3) Not only electrical irritation leaves a
 modification which goes to swell the following stimulus, but every
 sort of irritant which can produce a contraction does so. If in any
 way a reflex contraction of the muscle experimented on has been
 produced, or if it is contracted spontaneously by the animal (as not
 unfrequently happens 'by sympathy,' during a deep inspiration), it is
 found that an electrical stimulus, until then inoperative, operates
 energetically if immediately applied."[101]

Furthermore:

 "In a certain stage of the morphia-narcosis an ineffectively weak
 shock will become powerfully effective, if, immediately before its
 application to the motor centre, the skin of certain parts of
 the body is exposed to gentle tactile stimulation.... If, having
 ascertained the subminimal strength of current and convinced one's
 self repeatedly of its inefficacy, we draw our hand a single time
 lightly over the skin of the paw whose cortical centre is the object
 of stimulation, we find the current at once strongly effective. The
 increase of irritability lasts some seconds before it disappears.
 Sometimes the effect of a single light stroking of the paw is only
 sufficient to make the previously ineffectual current produce a very
 weak contraction. Repeating the tactile stimulation will then, as a
 rule, increase the contraction's extent."[102]

We constantly use the summation of stimuli in our practical appeals.
If a car-horse balks, the final way of starting him is by applying
a number of customary incitements at once. If the driver uses reins
and voice, if one bystander pulls at his head, another lashes his
hind quarters, and the conductor rings the bell, and the dismounted
passengers shove the car, all at the same moment, his obstinacy
generally yields, and he goes on his way rejoicing. If we are striving
to remember a lost name or fact, we think of as many 'cues' as
possible, so that by their joint action they may recall what no one
of them can recall alone. The sight of a dead prey will often not
stimulate a beast to pursuit, but if the sight of movement be added to
that of form, pursuit occurs. "Brücke noted that his brainless hen,
which made no attempt to peck at the grain under her very eyes, began
pecking if the grain were thrown on the ground with force, so as to
produce a rattling sound."[103] "Dr. Allen Thomson hatched out some
chickens on a carpet, where he kept them for several days. They showed
no inclination to scrape,... but when Dr. Thomson sprinkled a little
gravel on the carpet,... the chickens immediately began their scraping
movements."[104] A strange person, and darkness, are both of them
stimuli to fear and mistrust in dogs (and for the matter of that, in
men). Neither circumstance alone may awaken outward manifestations,
but together, i.e. when the strange man is met in the dark, the dog
will be excited to violent defiance.[105] Street-hawkers well know the
efficacy of summation, for they arrange themselves in a line upon the
sidewalk, and the passer often buys from the last one of them, through
the effect of the reiterated solicitation, what he refused to buy from
the first in the row. Aphasia shows many examples of summation. A
patient who cannot name an object simply shown him, will name it if he
touches as well as sees it, etc.

Instances of summation might be multiplied indefinitely, but it is
hardly worth while to forestall subsequent chapters. Those on Instinct,
the Stream of Thought, Attention, Discrimination, Association, Memory,
Æsthetics, and Will, will contain numerous exemplifications of the
reach of the principle in the purely psychological field.

REACTION-TIME.

One of the lines of experimental investigation most diligently followed
of late years is that of the ascertainment of the _time occupied by
nervous events_. Helmholtz led off by discovering the rapidity of
the current in the sciatic nerve of the frog. But the methods he
used were soon applied to the sensory nerves and the centres, and
the results caused much popular scientific admiration when described
as measurements of the 'velocity of thought.' The phrase 'quick as
thought' had from time immemorial signified all that was wonderful and
elusive of determination in the line of speed; and the way in which
Science laid her doomful hand upon this mystery reminded people of the
day when Franklin first '_eripuit cœlo fulmen_,' foreshadowing the
reign of a newer and colder race of gods. We shall take up the various
operations measured, each in the chapter to which it more naturally
pertains. I may say, however, immediately, that the phrase 'velocity
of _thought_' is misleading, for it is by no means clear in any of the
cases what particular act of thought occurs during the time which is
measured. 'Velocity of nerve-action' is liable to the same criticism,
for in most cases we do not know what particular nerve-processes occur.
What the times in question really represent is the total duration of
certain _reactions upon stimuli_. Certain of the conditions of the
reaction are prepared beforehand; they consist in the assumption of
those motor and sensory tensions which we name the expectant state.
Just what happens during the actual time occupied by the reaction (in
other words, just what is added to the pre-existent tensions to produce
the actual discharge) is not made out at present, either from the
neural or from the mental point of view.

The method is essentially the same in all these investigations. A
signal of some sort is communicated to the subject, and at the same
instant records itself on a time-registering apparatus. The subject
then makes a muscular movement of some sort, which is the 'reaction,'
and which also records itself automatically. The time found to have
elapsed between the two records is the total time of that observation.
The time-registering instruments are of various types. One type is
that of the revolving drum covered with smoked paper, on which one
electric pen traces a line which the signal breaks and the 'reaction'
draws again; whilst another electric pen (connected with a pendulum
or a rod of metal vibrating at a known rate) traces alongside of the
former line a 'time-line' of which each undulation or link stands
for a certain fraction of a second, and against which the break in
the reaction-line can be measured. Compare Fig. 21, where the line is
broken by the signal at the first arrow, and continued again by the
reaction at the second. Ludwig's Kymograph, Marey's Chronograph are
good examples of this type of instrument.

[Illustration: FIG. 21.]

Another type of instrument is represented by the stopwatch, of which
the most perfect form is Hipp's Chronoscope. The hand on the dial
measures intervals as short as 1/1000 of a second. The signal (by
an appropriate electric connection) starts it; the reaction stops
it; and by reading off its initial and terminal positions we have
immediately and with no farther trouble the time we seek. A still
simpler instrument, though one not very satisfactory in its working,
is the 'psychodometer' of Exner & Obersteiner, of which I picture a
modification devised by my colleague Professor H. P. Bowditch, which
works very well.

[Illustration: FIG. 22.--Bowditch's Reaction-timer. _F_, tuning-fork
carrying a little plate which holds the paper on which the electric pen
_M_ makes the tracing, and sliding in grooves on the base-board. _P_,
a plug which spreads the prongs of the fork apart when it is pushed
forward to its extreme limit, and releases them when it is drawn back
to a certain point. The fork then vibrates, and, its backward movement
continuing, an undulating line is drawn on the smoked paper by the
pen. At _T_ is a tongue fixed to the carriage of the fork, and at _K_
an electric key which the tongue opens and with which the electric pen
is connected. At the instant of opening, the pen changes its place and
the undulating line is drawn at a different level on the paper. The
opening can be made to serve as a signal to the reacter in a variety
of ways, and his reaction can be made to close the pen again, when the
line returns to its first level. The reaction time = the number of
undulations traced at the second level.]

The manner in which the signal and reaction are connected with the
chronographic apparatus varies indefinitely in different experiments.
Every new problem requires some new electric or mechanical disposition
of apparatus.[106]

The least complicated time-measurement is that known as _simple
reaction-time_, in which there is but one possible signal and one
possible movement, and both are known in advance. The movement is
generally the closing of an electric key with the hand. The foot,
the jaw, the lips, even the eyelid, have been in turn made organs of
reaction, and the apparatus has been modified accordingly.[107] The
time usually elapsing between stimulus and movement lies between one
and three tenths of a second, varying according to circumstances which
will be mentioned anon.

The subject of experiment, whenever the reactions are short and
regular, is in a state of extreme tension, and feels, when the signal
comes, as if _it_ started the reaction, by a sort of fatality, and
as if no psychic process of perception or volition had a chance to
intervene. The whole succession is so rapid that perception seems to be
retrospective, and the time-order of events to be read off in memory
rather than known at the moment. This at least is my own personal
experience in the matter, and with it I find others to agree. The
question is, What happens inside of us, either in brain or mind? and to
answer that we must analyze just what processes the reaction involves.
It is evident that some time is lost in each of the following stages:

1. The stimulus excites the peripheral sense-organ adequately for a
current to pass into the sensory nerve;

2. The sensory nerve is traversed;

3. The transformation (or reflection) of the sensory into a motor
current occurs in the centres;

4. The spinal cord and motor nerve are traversed;

5. The motor current excites the muscle to the contracting point.

Time is also lost, of course, outside the muscle, in the joints, skin,
etc., and between the parts of the apparatus; and when the stimulus
which serves as signal is applied to the skin of the trunk or limbs,
time is lost in the sensorial conduction through the spinal cord.

The stage marked 3 is the only one that interests us here. The other
stages answer to purely physiological processes, but stage 3 is
psycho-physical; that is, it is a higher-central process, and has
probably some sort of consciousness accompanying it. What sort?

Wundt has little difficulty in deciding that it is consciousness of
a quite elaborate kind. He distinguishes between two stages in the
conscious reception of an impression, calling one _perception_, and the
other _apperception_, and likening the one to the mere entrance of an
object into the periphery of the field of vision, and the other to its
coming to occupy the focus or point of view. _Inattentive awareness_
of an object, and _attention_ to it, are, it seems to me, equivalents
for perception and apperception, as Wundt uses the words. To these two
forms of awareness of the impression Wundt adds the conscious volition
to react, gives to the trio the name of 'psycho-physical' processes,
and assumes that they actually follow upon each other in the succession
in which they have been named.[108] So at least I understand him. The
simplest way to determine the time taken up by this psycho-physical
stage No. 3 would be to determine separately the duration of the
several purely physical processes, 1, 2, 4, and 5, and to subtract them
from the total reaction-time. Such attempts have been made.[109] But
the data for calculation are too inaccurate for use, and, as Wundt
himself admits,[110] the precise duration of stage 3 must at present
be left enveloped with that of the other processes, in the total
reaction-time.

My own belief is that no such succession of conscious feelings as
Wundt describes takes place during stage 3. It is a process of central
excitement and discharge, with which doubtless some feeling coexists,
but _what_ feeling we cannot tell, because it is so fugitive and so
immediately eclipsed by the more substantive and enduring memory
of the impression as it came in, and of the executed movement of
response. Feeling of the impression, attention to it, thought of
the reaction, volition to react, _would_, undoubtedly, all be links
of the process _under other conditions_,[111] and would lead to the
same reaction--after an indefinitely longer time. But these other
conditions are not those of the experiments we are discussing; and it
is mythological psychology (of which we shall see many later examples)
to conclude that because two mental processes lead to the same result
they must be similar in their inward subjective constitution. The
feeling of stage 3 is certainly no articulate perception. It can be
nothing but the mere sense of a reflex discharge. _The reaction whose
time is measured is_, in short, _a reflex action pure and simple, and
not a psychic act_. A foregoing psychic condition is, it is true, a
prerequisite for this reflex action. The preparation of the attention
and volition; the expectation of the signal and the readiness of the
hand to move, the instant it shall come; the nervous tension in which
the subject waits, are all conditions of the formation in him for the
time being of a new path or arc of reflex discharge. The tract from
the sense-organ which receives the stimulus, into the motor centre
which discharges the reaction, is already tingling with premonitory
innervation, is raised to such a pitch of heightened irritability by
the expectant attention, that the signal is instantaneously sufficient
to cause the overflow.[112] No other tract of the nervous system is,
at the moment, in this hair-trigger condition. The consequence is
that one sometimes responds to a _wrong_ signal, especially if it be
an impression of the same _kind_ with the signal we expect.[113] But
if by chance we are tired, or the signal is unexpectedly weak, and
we do not react instantly, but only after an express perception that
the signal has come, and an express volition, the time becomes quite
disproportionately long (a second or more, according to Exner[114]),
and we feel that the process is in nature altogether different.

In fact, the reaction-time experiments are a case to which we can
immediately apply what we have just learned about the summation of
stimuli. 'Expectant attention' is but the subjective name for what
objectively is a partial stimulation of a certain pathway, the pathway
from the 'centre' for the signal to that for the discharge. In Chapter
XI we shall see that all attention involves excitement from within
of the tract concerned in feeling the objects to which attention is
given. The tract here is the excito-motor arc about to be traversed.
The signal is but the spark from without which touches off a train
already laid. The performance, under these conditions, exactly
resembles any reflex action. The only difference is that whilst, in the
ordinarily so-called reflex acts, the reflex arc is a permanent result
of organic growth, it is here a transient result of previous cerebral
conditions.[115]

I am happy to say that since the preceding paragraphs (and the
notes thereto appertaining) were written, Wundt has himself become
converted to the view which I defend. He now admits that in the
shortest reactions "there is neither apperception nor will, but that
they are merely _brain-reflexes due to practice_."[116] The means of
his conversion are certain experiments performed in his laboratory
by Herr L. Lange,[117] who was led to distinguish between two ways
of setting the attention in reacting on a signal, and who found that
they gave very different time-results. In the '_extreme sensorial_'
way, as Lange calls it, of reacting, one keeps one's mind as intent
as possible upon the expected signal, and 'purposely avoids'[118]
thinking of the movement to be executed; in the '_extreme muscular_'
way one 'does not think at all'[119] of the signal, but stands as
ready as possible for the movement. The muscular reactions are much
shorter than the sensorial ones, the average difference being in the
neighborhood of a tenth of a second. Wundt accordingly calls them
'shortened reactions' and, with Lange, admits them to be mere reflexes;
whilst the sensorial reactions he calls 'complete,' and holds to his
original conception as far as they are concerned. The facts, however,
do not seem to me to warrant even this amount of fidelity to the
original Wundtian position. When we begin to react in the 'extreme
sensorial' way, Lange says that we get times so very long that they
must be rejected from the count as non-typical. "Only after the reacter
has succeeded by repeated and conscientious practice in bringing about
an extremely precise co-ordination of his voluntary impulse with his
sense-impression do we get times which can be regarded as typical
sensorial reaction-times."[120] Now it seems to me that these excessive
and 'untypical' times are probably the real 'complete times,' the only
ones in which distinct processes of actual perception and volition
occur (see above, pp. 88-9). The typical sensorial time which is
attained by practice is probably another sort of reflex, less perfect
than the reflexes prepared by straining one's attention towards the
movement.[121] The times are much more variable in the sensorial way
than in the muscular. The several muscular reactions differ little
from each other. Only in them does the phenomenon occur of reacting on
a false signal, or of reacting before the signal. Times intermediate
between these two types occur according as the attention fails to turn
itself exclusively to one of the extremes. It is obvious that Herr
Lange's distinction between the two types of reaction is a highly
important one, and that the 'extreme muscular method,' giving both the
shortest times and the most constant ones, ought to be aimed at in all
comparative investigations. Herr Lange's own muscular time averaged
0''.123; his sensorial time, 0''.230.

These reaction-time experiments are then in no sense measurements of
the swiftness of _thought_. Only when we complicate them is there a
chance for anything like an intellectual operation to occur. They
may be complicated in various ways. The reaction may be withheld
until the signal has consciously awakened a distinct idea (Wundt's
discrimination-time, association-time) and then performed. Or there
may be a variety of possible signals, each with a different reaction
assigned to it, and the reacter may be uncertain which one he is about
to receive. The reaction would then hardly seem to occur without a
preliminary recognition and choice. We shall see, however, in the
appropriate chapters, that the discrimination and choice involved in
such a reaction are widely different from the intellectual operations
of which we are ordinarily conscious under those names. Meanwhile
the simple reaction-time remains as the starting point of all these
superinduced complications. It is the fundamental physiological
constant in all time-measurements. As such, its own variations have an
interest, and must be briefly passed in review.[122]

The reaction-time varies with the _individual_ and his _age_. An
individual may have it particularly long in respect of signals of one
sense (Buccola, p. 147), but not of others. Old and uncultivated people
have it long (nearly a second, in an old pauper observed by Exner,
Pflüger's Archiv, vii, 612-4). Children have it long (half a second,
Herzen in Buccola, p. 152).

_Practice_ shortens it to a quantity which is for each individual a
minimum beyond which no farther reduction can be made. The aforesaid
old pauper's time was, after much practice, reduced to 0.1866 sec.
(_loc. cit._ p. 626).

_Fatigue_ lengthens it.

_Concentration of attention_ shortens it. Details will be given in the
chapter on Attention.

The _nature of the signal_ makes it vary.[123] Wundt writes:

 "I found that the reaction-time for impressions on the skin with
 electric stimulus is less than for true touch-sensations, as the
 following averages show:

                              Average.    Average Variation

   Sound                      0.167 sec.  0.0221 sec.

   Light                      0.222 sec.  0.0219 sec.

   Electric skin-sensation    0.201 sec.  0.0115 sec.

   Touch-sensations           0.213 sec.  0.0134 sec.

 "I here bring together the averages which have been obtained by some
 other observers:

                  Hirsch.  Hankel.  Exner.

  Sound           0.149    0.1505   0.1360

  Light           0.200    0.2246   0.1506

  Skin-sensation  0.182    0.1546   0.1337"[124]

_Thermic_ reactions have been lately measured by A. Goldscheider
and by Vintschgau (1887), who find them slower than reactions from
touch. That from heat especially is very slow, more so than from
cold, the differences (according to Goldscheider) depending on the
nerve-terminations in the skin.

_Gustatory_ reactions were measured by Vintschgau. They differed
according to the substances used, running up to half a second as a
maximum when identification took place. The mere perception of the
presence of the substance on the tongue varied from 0''.159 to 0''.219
(Pflüger's Archiv, xiv, 529).

_Olfactory_ reactions have been studied by Vintschgau, Buccola, and
Beaunis. They are slow, averaging about half a second (cf. Beaunis,
Recherches exp. sur l'Activité Cérébrale, 1884, p. 49 ff.).

It will be observed that _sound_ is more promptly reacted on than
either _sight_ or _touch. Taste_ and _smell_ are slower than either.
One individual, who reacted to touch upon the tip of the tongue in
0''.125, took 0''.993 to react upon the taste of quinine applied to
the same spot. In another, upon the base of the tongue, the reaction
to touch being 0''.141, that to sugar was 0''.552 (Vintschgau, quoted
by Buccola, p. 103). Buccola found the reaction to odors to vary from
0''.334 to 0''.681, according to the perfume used and the individual.

The _intensity of the signal_ makes a difference. The intenser the
stimulus the shorter the time. Herzen (Grundlinien einer allgem.
Psychophysiologie, p. 101) compared the reaction from a _corn_ on
the toe with that from the skin of the hand of the same subject. The
two places were stimulated simultaneously, and the subject tried to
react simultaneously with both hand and foot, but the foot always went
quickest. When the sound skin of the foot was touched instead of the
corn, it was the hand which always reacted first. Wundt tries to show
that when the signal is made barely perceptible, the time is probably
the same in all the senses, namely, about 0.332'' (Physiol. Psych., 2d
ed., ii, 224).

Where the signal is of touch, the place to which it is applied makes
a difference in the resultant reaction-time. G. S. Hall and V. Kries
found (Archiv f. Anat. u. Physiol., 1879) that when the finger-tip
was the place the reaction was shorter than when the middle of the
upper arm was used, in spite of the greater length of nerve-trunk
to be traversed in the latter case. This discovery invalidates the
measurements of the rapidity of transmission of the current in
human nerves, for they are all based on the method of comparing
reaction-times from places near the root and near the extremity of
a limb. The same observers found that signals seen by the periphery
of the retina gave longer times than the same signals seen by direct
vision.

The _season_ makes a difference, the time being some hundredths of a
second shorter on cold winter days (Vintschgau _apud_ Exner, Hermann's
Hdbh., p. 270).

_Intoxicants_ alter the time. _Coffee_ and _tea_ appear to shorten it.
Small doses of _wine_ and _alcohol_ first shorten and then lengthen it;
but the shortening stage tends to disappear if a large dose be given
immediately. This, at least, is the report of two German observers. Dr.
J. W. Warren, whose observations are more thorough than any previous
ones, could find no very decided effects from ordinary doses (Journal
of Physiology, viii, 311). _Morphia_ lengthens the time. _Amyl-nitrite_
lengthens it, but after the inhalation it may fall to less than the
normal. Ether and chloroform lengthen it (for authorities, etc., see
Buccola, p. 189).

Certain _diseased states_ naturally lengthen the time.

The _hypnotic trance_ has no constant effect, sometimes shortening and
sometimes lengthening it (Hall, Mind, viii, 170; James, Proc. Am. Soc.
for Psych. Research, 246).

The time taken to _inhibit_ a movement (e.g. to cease contraction of
jaw-muscles) seems to be about the same as to produce one (Gad, Archiv
f. (Anat. u.) Physiol., 1887, 468; Orchansky, _ibid._1889, 1885).

An immense amount of work has been done on reaction-time, of which
I have cited but a small part. It is a sort of work which appeals
particularly to patient and exact minds, and they have not failed to
profit by the opportunity.

CEREBRAL BLOOD-SUPPLY.

The next point to occupy our attention is the _changes of circulation
which accompany cerebral activity_.

[Illustration: FIG. 23.--Sphymographic pulse-tracing. _A_, during
intellectual repose; _B_, during intellectual activity. (Mosso.)]

All parts of the cortex, when electrically excited, produce alterations
both of respiration and circulation. The blood-pressure rises, as a
rule, all over the body, no matter where the cortical irritation is
applied, though the motor zone is the most sensitive region for the
purpose. Elsewhere the current must be strong enough for an epileptic
attack to be produced.[125] Slowing and quickening of the heart are
also observed, and are independent of the vaso-constrictive phenomenon.
Mosso, using his ingenious 'plethysmograph' as an indicator,
discovered that the blood-supply to the arms diminished during
intellectual activity, and found furthermore that the arterial tension
(as shown by the sphygmograph) was increased in these members (see Fig.
23). So slight an emotion as that produced by the entrance of Professor
Ludwig into the laboratory was instantly followed by a shrinkage of the
arms.[126] The brain itself is an excessively vascular organ, a sponge
full of blood, in fact; and another of Mosso's inventions showed that
when less blood went to the arms, more went to the head. The subject
to be observed lay on a delicately balanced table which could tip
downward either at the head or at the foot if the weight of either end
were increased. The moment emotional or intellectual activity began
in the subject, down went the balance at the head-end, in consequence
of the redistribution of blood in his system. But the best proof of
the immediate afflux of blood to the brain during mental activity is
due to Mosso's observations on three persons whose brain had been laid
bare by lesion of the skull. By means of apparatus described in his
book,[127] this physiologist was enabled to let the brain-pulse record
itself directly by a tracing. The intra-cranial blood-pressure rose
immediately whenever the subject was spoken to, or when he began to
think actively, as in solving a problem in mental arithmetic. Mosso
gives in his work a large number of reproductions of tracings which
show the instantaneity of the change of blood-supply, whenever the
mental activity was quickened by any cause whatever, intellectual or
emotional. He relates of his female subject that one day whilst tracing
her brain-pulse he observed a sudden rise with no apparent outer or
inner cause. She however confessed to him afterwards that at that
moment she had caught sight of a _skull_ on top of a piece of furniture
in the room, and that this had given her a slight emotion.

The fluctuations of the blood supply to the brain were independent
of respiratory changes,[128] and followed the quickening of mental
activity almost immediately. We must suppose a very delicate adjustment
whereby the circulation follows the needs of the cerebral activity.
Blood very likely may rush to each region of the cortex according as
it is most active, but of this we know nothing. I need hardly say that
the activity of the nervous matter is the primary phenomenon, and the
afflux of blood its secondary consequence. Many popular writers talk
as if it were the other way about, and as if mental activity were due
to the afflux of blood. But, as Professor H. N. Martin has well said,
"that belief has no physiological foundation whatever; it is even
directly opposed to all that we know of cell life."[129] A chronic
pathological congestion may, it is true, have secondary consequences,
but the primary congestions which we have been considering _follow_ the
activity of the brain-cells by an adaptive reflex vaso-motor mechanism
doubtless as elaborate as that which harmonizes blood-supply with
cell-action in any muscle or gland.

Of the changes in the cerebral circulation during sleep I will speak in
the chapter which treats of that subject.

CEREBRAL THERMOMETRY.

_Brain-activity seems accompanied by a local disengagement of heat._
The earliest careful work in this direction was by Dr. J. S. Lombard in
1867. Dr. Lombard's latest results include the records of over 60,000
observations.[130] He noted the changes in delicate thermometers and
electric piles placed against the scalp in human beings, and found
that any intellectual effort, such as computing, composing, reciting
poetry silently or aloud, and especially that emotional excitement
such as an anger fit, caused a general rise of temperature, which
rarely exceeded a degree Fahrenheit. The rise was in most cases more
marked in the middle region of the head than elsewhere. Strange to
say, it was greater in reciting poetry silently than in reciting it
aloud. Dr. Lombard's explanation is that "in internal recitation an
additional portion of energy, which in recitation aloud was converted
into nervous and muscular force, now appears as heat."[131] I should
suggest rather, if we must have a theory, that the surplus of heat
in recitation to one's self is due to inhibitory processes which are
absent when we recite aloud. In the chapter on the Will we shall see
that the _simple_ central process is to _speak_ when we think; to
think silently involves a check in addition. In 1870 the indefatigable
Schiff took up the subject, experimenting on live dogs and chickens,
plunging thermo-electric needles into the substance of their brain,
to eliminate possible errors from vascular changes in the skin when
the thermometers were placed upon the scalp. After habituation was
established, he tested the animals with various sensations, tactile,
optic, olfactory, and auditory. He found very regularly an immediate
deflection of the galvanometer, indicating an abrupt alteration of
the intra-cerebral temperature. When, for instance, he presented an
empty roll of paper to the nose of his dog as it lay motionless, there
was a small deflection, but when a piece of meat was in the paper the
deflection was much greater. Schiff concluded from these and other
experiments that sensorial activity heats the brain-tissue, but he did
not try to localize the increment of heat beyond finding that it was
in both hemispheres, whatever might be the sensation applied.[132] Dr.
R. W. Amidon in 1880 made a farther step forward, in localizing the
heat produced by voluntary muscular contractions. Applying a number
of delicate surface-thermometers simultaneously against the scalp, he
found that when different muscles of the body were made to contract
vigorously for ten minutes or more, different regions of the scalp rose
in temperature, that the regions were well focalized, and that the
rise of temperature was often considerably over a Fahrenheit degree.
As a result of his investigations he gives a diagram in which numbered
regions represent the centres of highest temperature for the various
special movements which were investigated. To a large extent they
correspond to the centres for the same movements assigned by Ferrier
and others on other grounds; only they cover more of the skull.[133]

_Phosphorus and Thought._

_Chemical action must of course accompany brain-activity._ But little
definite is known of its exact nature. Cholesterin and creatin are both
excrementitious products, and are both found in the brain. The subject
belongs to chemistry rather than to psychology, and I only mention it
here for the sake of saying a word about a wide-spread popular error
about brain-activity and phosphorus. '_Ohne Phosphor, kein Gedanke_,'
was a noted war-cry of the 'materialists' during the excitement on that
subject which filled Germany in the '60s. The brain, like every other
organ of the body, contains phosphorus, and a score of other chemicals
besides. Why the phosphorus should be picked out as its essence, no one
knows. It would be equally true to say 'Ohne Wasser kein Gedanke,' or
'Ohne Kochsalz kein Gedanke'; for thought would stop as quickly if the
brain should dry up or lose its NaCl as if it lost its phosphorus. In
America the phosphorus-delusion has twined itself round a saying quoted
(rightly or wrongly) from Professor L. Agassiz, to the effect that
fishermen are more intelligent than farmers because they eat so much
fish, which contains so much phosphorus. All the facts may be doubted.

The only straight way to ascertain the importance of phosphorus to
thought would be to find whether more is excreted by the brain during
mental activity than during rest. Unfortunately we cannot do this
directly, but can only gauge the amount of PO_{5} in the urine, which
represents other organs as well as the brain, and this procedure,
as Dr. Edes says, is like measuring the rise of water at the mouth
of the Mississippi to tell where there has been a thunder-storm
in Minnesota.[134] It has been adopted, however, by a variety of
observers, some of whom found the phosphates in the urine diminished,
whilst others found them increased, by intellectual work. On the whole,
it is impossible to trace any constant relation. In maniacal excitement
less phosphorus than usual seems to be excreted. More is excreted
during sleep. There are differences between the alkaline and earthy
phosphates into which I will not enter, as my only aim is to show that
the popular way of looking at the matter has no exact foundation.[135]
The fact that phosphorus-preparations may do good in nervous exhaustion
proves nothing as to the part played by phosphorus in mental activity.
Like iron, arsenic, and other remedies it is a stimulant or tonic, of
whose intimate workings in the system we know absolutely nothing, and
which moreover does good in an extremely small number of the cases in
which it is prescribed.

The phosphorus-philosophers have often compared thought to a secretion.
"The brain secretes thought, as the kidneys secrete urine, or as the
liver secretes bile," are phrases which one sometimes hears. The lame
analogy need hardly be pointed out. The materials which the brain
_pours into the blood_ (cholesterin, creatin, xanthin, or whatever they
may be) are the analogues of the urine and the bile, being in fact real
material excreta. As far as these matters go, the brain is a ductless
gland. But we know of nothing connected with liver-and kidney-activity
which can be in the remotest degree compared with the stream of
thought that accompanies the brain's material secretions.

There remains another feature of general brain-physiology, and indeed
for psychological purposes the most important feature of all. I refer
to the aptitude of the brain for acquiring _habits_. But I will treat
of that in a chapter by itself.

FOOTNOTES:

[99] I shall myself in later places indulge in much of this
schematization. The reader will understand once for all that it is
symbolic; and that the use of it is hardly more than to show what
a deep congruity there is between mental processes and mechanical
processes of _some_ kind, not necessarily of the exact kind portrayed.

[100] Valentin: Archiv f. d. gesammt. Physiol., 1873, p. 458. Stirling:
Leipzig Acad. Berichte, 1875, p. 372 (Journal of Physiol., 1875). J.
Ward: Archiv f. (Anat. u.) Physiol., 1880, p. 72. H. Sewall: Johns
Hopkins Studies, 1880, p. 30. Kronecker u. Nicolaides: Archiv f. (Anat.
u.) Physiol., 1880, p. 437. Exner: Archiv f. die ges. Physiol., Bd.
28, p. 487 (1882). Eckhard: in Hermann's Hdbch. d. Physiol., Bd. I,
Thl. ii, p. 31. François-Franck: Leçons sur les Fonctions motrices du
Cerveau, p. 51 ff., 339.--For the process of summation in _nerves_ and
_muscles_, cf. Hermann: _ibid._ Thl. i, p. 109, and vol. i, p. 40. Also
Wundt: Physiol. Psych., i, 243 ff.; Richet: Travaux du Laboratoire de
Marey, 1877, p. 97; L'Homme et l'Intelligence, pp. 24 ff., 468; Revue
Philosophique, t. xxi, p. 564. Kronecker u. Hall: Archiv f. (Anat. u.)
Physiol., 1879; Schönlein: _ibid._1882, p. 357. Sertoli (Hofmann and
Schwalbe's Jahres-bericht), 1882, p. 25. De Watteville: Neurologisches
Centralblatt, 1883, No. 7. Grünhagen: Arch. f. d. ges. Physiol., Bd.
34, p. 301 (1884).

[101] Bubnoff und Heidenhain: Ueber Erregungs- und Hemmungsvorgänge
innerhalb der motorischen Hirncentren. Archiv f. d. ges. Physiol., Bd.
26, p. 156 (1881).

[102] Archiv f. d. ges. Physiol., Bd. 26, p. 176 (1881). Exner thinks
(_ibid._ Bd. 28, p. 497 (1882)) that the summation here occurs in the
spinal cord. It makes no difference where this particular summation
occurs, so far as the general philosophy of summation goes.

[103] G H. Lewes: Physical Basis of Mind, p. 479, where many similar
examples are given, 487-9.

[104] Romanes: Mental Evolution in Animals, p. 168.

[105] See a similar instance in Mach: Beiträge zur Analyse der
Empfindungen, p. 36, a sparrow being the animal. My young children are
afraid of their own pug-dog, if he enters their room after they are in
bed and the lights are out. Compare this statement also: "The first
question to a peasant seldom proves more than a flapper to rouse the
torpid adjustments of his ears. The invariable answer of a Scottish
peasant is, 'What's your wull?'--that of the English, a vacant stare. A
second and even a third question may be required to elicit an answer."
(R. Fowler; Some Observations on the Mental State of the Blind, and
Deaf, and Dumb (Salisbury, 1843), p. 14.)

[106] The reader will find a great deal about chronographic apparatus
in J. Marey: La Méthode Graphique, pt. ii, chap. ii. One can make
pretty fair measurements with no other instrument than a watch, by
making a large number of reactions, each serving as a signal for
the following one, and dividing the total time they take by their
number. Dr. O. W. Holmes first suggested this method, which has been
ingeniously elaborated and applied by Professor Jastrow. See 'Science'
for September 10, 1886.

[107] See, for a few modifications, Cattell, Mind, xi, 220 ff.

[108] Physiol. Psych., ii, 221-2. Cf. also the first edition, 728-9.
I must confess to finding all Wundt's utterances about 'apperception'
both vacillating and obscure. I see no use whatever for the word, as he
employs it, in Psychology. Attention, perception, conception, volition,
are its ample equivalents. Why we should need a single word to denote
all these things by turns, Wundt fails to make clear. Consult, however,
his pupil Staude's article, 'Ueber den Begriff der Apperception,' etc.,
in Wundt's periodical Philosophische Studien, i, 149, which may be
supposed official. For a minute criticism of Wundt's 'apperception,'
see Marty: Vierteljahrschrift f. wiss. Philos., x, 346.

[109] By Exner, for example, Pflüger's Archiv, vii, 628 ff.

[110] P. 222. Cf. also Richet, Rev. Philos., vi, 395-6.

[111] For instance, if, on the previous day, one had resolved to act on
a signal when it should come, and it now came whilst we were engaged in
other things, and reminded us of the resolve.

[112] "I need hardly mention that success in these experiments depends
in a high degree on our concentration of attention. If inattentive, one
gets very discrepant figures.... This concentration of the attention
is in the highest degree exhausting. After some experiments in which I
was concerned to get results as uniform as possible, I was covered with
perspiration and excessively fatigued although I had sat quietly in my
chair all the while." (Exner, _loc. cit._ vii, 618.)

[113] Wundt, Physiol. Psych., ii, 226

[114] Pflüger's Archiv, vii, 616.

[115] In short, what M. Delbœuf calls an '_organe adventice_.' The
reaction-time, moreover, is quite compatible with the reaction itself
being of a reflex order. Some reflexes (sneezing, e.g.) are very slow.
The only time-measurement of a reflex act in the human subject with
which I am acquainted is Exner's measurement of winking (in Pflüger's
Archiv f. d. gesammt. Physiol., Bd. viii, p. 526, 1874). He found that
when the stimulus was a flash of light it took the wink 0.2168 sec.
to occur. A strong electric shock to the cornea shortened the time
to 0.0578 sec. The ordinary 'reaction-time' is midway between these
values. Exner 'reduces' his times by eliminating the physiological
process of conduction. His 'reduced minimum winking-time' is then
0.0471 (_ibid._ 531), whilst his reduced reaction-time is 0.0828
(_ibid._ vii, 637). These figures have really no scientific value
beyond that of showing, according to Exner's own belief (vii, 531),
that reaction-time and reflex-time measure processes of essentially
the same order. His description, moreover, of the process is an
excellent description of a reflex act. "Every one," says he, "who
makes reaction-time experiments for the first time is surprised to
find how little he is master of his own movements, so soon as it
becomes a question of executing them with a maximum of speed. Not only
does their energy lie, as it were, outside the field of choice, but
even the time in which the movement occurs depends only partly upon
ourselves. We jerk our arm, and we can afterwards tell with astonishing
precision whether we have jerked it quicker or slower than another
time, although we have no power to jerk it exactly at the wished-for
moment."--Wundt himself admits that when we await a strong signal
with tense preparation there is no consciousness of any duality of
'apperception' and motor response; the two are continuous (Physiol.
Psych., ii, 226).--Mr. Cattell's view is identical with the one I
defend. "I think," he says, "that if the processes of perception and
willing are present at all they are very rudimentary.... The subject,
by a voluntary effort [before the signal comes], puts the lines of
communication between the centre for" the stimulus "and the centre for
the co-ordination of motions ... in a state of unstable equilibrium.
When, therefore, a nervous impulse reaches the" former centre, "it
causes brain-changes in two directions; an impulse moves along to
the cortex and calls forth there a perception corresponding to the
stimulus, while at the same time an impulse follows a line of small
resistance to the centre for the co-ordination of motions, and the
proper nervous impulse, already prepared and waiting for the signal,
is sent from the centre to the muscle of the hand. When the reaction
has often been made the entire cerebral process becomes automatic, the
impulse of itself takes the well-travelled way to the motor centre, and
releases the motor impulse." (Mind, xi, 232-3.)--Finally, Prof. Lipps
has, in his elaborate way (Grundtatsachen, 179-188), made mince-meat of
the view that stage 3 involves either conscious perception or conscious
will.

[116] Physiol. Psych., 3d edition (1887), vol. ii, p. 266.

[117] Philosophische Studien, vol. iv, p. 479 (1888).

[118] _Loc. cit._ p. 488.

[119] _Loc. cit._ p. 487.

[120] _Loc. cit._ p. 489.

[121] Lange has an interesting hypothesis as to the brain-process
concerned in the latter, for which I can only refer to his essay.

[122] The reader who wishes to know more about the matter will find
a most faithful compilation of all that has been done, together with
much original matter, in G. Buccola's 'Legge del Tempo,' etc. See also
chapter xvi of Wundt's Physiol. Psychology; Exner in Hermann's Hdbch.,
Bd. 2, Thl. ii, pp. 252-280; also Ribot's Contemp. Germ. Psych. chap.
viii.

[123] The nature of the movement also seems to make it vary. Mr. B. I.
Gilman and I reacted to the same signal by simply raising our hand, and
again by carrying our hand towards our back. The moment registered was
always that at which the hand broke an electric contact in _starting_
to move. But it started one or two hundredths of a second later when
the more extensive movement was the one to be made. Orchansky, on the
other hand, experimenting on contractions of the masseter muscle,
found (Archiv f. (Anat. u.) Physiol., 1889, p. 187) that the greater
the amplitude of contraction intended, the shorter grew the time of
reaction. He explains this by the fact that a more ample contraction
makes a greater _appeal to the attention_, and that this shortens the
times.

[124] Physiol. Psych., ii, 223.

[125] François-Franck, Fonctions Motrices, Leçon xxii.

[126] La Paura (1884), p. 117.

[127] Ueber den Kreislauf des Blutes im menschlichen Gehirn (1881),
chap. ii. The Introduction gives the history of our previous knowledge
of the subject.

[128] In this conclusion M. Gley (Archives de Physiologie, 1881, p.
742) agrees with Professor Mosso. Gley found his pulse rise 1-3 beats,
his carotid dilate, and his radial artery contract during hard mental
work.

[129] Address before Med. and Chirurg. Society of Maryland, 1879.

[130] See his book; "Experimental Researches on the Regional
Temperature of the Head" (London, 1879).

[131] _Loc. cit._ p. 195.

[132] The most convenient account of Schiff's experiments is by Prof.
Hierzen, in the Revue Philosophique, vol. iii, p. 36.

[133] A New Study of Cerebral Cortical Localization (N. Y., Putnam,
1880), pp. 48-53.

[134] Archives of Medicine, vol. x, No. 1 (1883).

[135] Without multiplying references, I will simply cite Mendel (Archiv
f. Psychiatrie, vol. iii, 1871), Mairet (Archives de Neurologie, vol.
ix, 1885), and Beaunis (Rech. Expérimentales sur l'Activité Cérébrale,
1887). Richet gives a partial bibliography in the Revue Scientifique,
vol. 38, p. 788 (1886).

CHAPTER IV.[136]

HABIT.

When we look at living creatures from an outward point of view, one of
the first things that strike us is that they are bundles of habits.
In wild animals, the usual round of daily behavior seems a necessity
implanted at birth; in animals domesticated, and especially in man, it
seems, to a great extent, to be the result of education. The habits to
which there is an innate tendency are called instincts; some of those
due to education would by most persons be called acts of reason. It
thus appears that habit covers a very large part of life, and that one
engaged in studying the objective manifestations of mind is bound at
the very outset to define clearly just what its limits are.

The moment one tries to define what habit is, one is led to the
fundamental properties of matter. The laws of Nature are nothing but
the immutable habits which the different elementary sorts of matter
follow in their actions and reactions upon each other. In the organic
world, however, the habits are more variable than this. Even instincts
vary from one individual to another of a kind; and are modified in the
same individual, as we shall later see, to suit the exigencies of the
case. The habits of an elementary particle of matter cannot change (on
the principles of the atomistic philosophy), because the particle is
itself an unchangeable thing; but those of a compound mass of matter
can change, because they are in the last instance due to the structure
of the compound, and either outward forces or inward tensions can, from
one hour to another, turn that structure into something different from
what it was. That is, they can do so if the body be plastic enough to
maintain its integrity, and be not disrupted when its structure yields.

The change of structure here spoken of need not involve the outward
shape; it may be invisible and molecular, as when a bar of iron
becomes magnetic or crystalline through the action of certain outward
causes, or India-rubber becomes friable, or plaster 'sets.' All these
changes are rather slow; the material in question opposes a certain
resistance to the modifying cause, which it takes time to overcome,
but the gradual yielding whereof often saves the material from being
disintegrated altogether. When the structure has yielded, the same
inertia becomes a condition of its comparative permanence in the new
form, and of the new habits the body then manifests. _Plasticity_,
then, in the wide sense of the word, means the possession of a
structure weak enough to yield to an influence, but strong enough not
to yield all at once. Each relatively stable phase of equilibrium in
such a structure is marked by what we may call a new set of habits.
Organic matter, especially nervous tissue, seems endowed with a very
extraordinary degree of plasticity of this sort; so that we may without
hesitation lay down as our first proposition the following, that _the
phenomena of habit in living beings are due to the plasticity[137] of
the organic materials of which their bodies are composed_.

But the philosophy of habit is thus, in the first instance, a chapter
in physics rather than in physiology or psychology. That it is at
bottom a physical principle is admitted by all good recent writers
on the subject. They call attention to analogues of acquired habits
exhibited by dead matter. Thus, M. Léon Dumont, whose essay on habit is
perhaps the most philosophical account yet published, writes:

 "Every one knows how a garment, after having been worn a certain
 time, clings to the shape of the body better than when it was new;
 there has been a change in the tissue, and this change is a new habit
 of cohesion. A lock works better after being used some time; at the
 outset more force was required to overcome certain roughnesses in
 the mechanism. The overcoming of their resistance is a phenomenon of
 habituation. It costs less trouble to fold a paper when it has been
 folded already. This saving of trouble is due to the essential nature
 of habit, which brings it about that, to reproduce the effect, a
 less amount of the outward cause is required. The sounds of a violin
 improve by use in the hands of an able artist, because the fibres of
 the wood at last contract habits of vibration conformed to harmonic
 relations. This is what gives such inestimable value to instruments
 that have belonged to great masters. Water, in flowing, hollows out
 for itself a channel, which grows broader and deeper; and, after
 having ceased to flow, it resumes, when it flows again, the path
 traced by itself before. Just so, the impressions of outer objects
 fashion for themselves in the nervous system more and more appropriate
 paths, and these vital phenomena recur under similar excitements from
 without, when they have been interrupted a certain time."[138]

Not in the nervous system alone. A scar anywhere is a _locus minoris
resistentiæ_, more liable to be abraded, inflamed, to suffer pain and
cold, than are the neighboring parts. A sprained ankle, a dislocated
arm, are in danger of being sprained or dislocated again; joints
that have once been attacked by rheumatism or gout, mucous membranes
that have been the seat of catarrh, are with each fresh recurrence
more prone to a relapse, until often the morbid state chronically
substitutes itself for the sound one. And if we ascend to the nervous
system, we find how many so-called functional diseases seem to keep
themselves going simply because they happen to have once begun; and
how the forcible cutting short by medicine of a few attacks is often
sufficient to enable the physiological forces to get possession of
the field again, and to bring the organs back to functions of health.
Epilepsies, neuralgias, convulsive affections of various sorts,
insomnias, are so many cases in point. And, to take what are more
obviously habits, the success with which a 'weaning' treatment can
often be applied to the victims of unhealthy indulgence of passion, or
of mere complaining or irascible disposition, shows us how much the
morbid manifestations themselves were due to the mere inertia of the
nervous organs, when once launched on a false career.

Can we now form a notion of what the inward physical changes may be
like, in organs whose habits have thus struck into new paths? In
other words, can we say just what mechanical facts the expression
'change of habit' covers when it is applied to a nervous system?
Certainly we cannot in anything like a minute or definite way. But our
usual scientific custom of interpreting hidden molecular events after
the analogy of visible massive ones enables us to frame easily an
abstract and general scheme of processes which the physical changes in
question _may_ be like. And when once the possibility of _some_ kind of
mechanical interpretation is established, Mechanical Science, in her
present mood, will not hesitate to set her brand of ownership upon the
matter, feeling sure that it is only a question of time when the exact
mechanical explanation of the case shall be found out.

If habits are due to the plasticity of materials to outward agents,
we can immediately see to what outward influences, if to any, the
brain-matter is plastic. Not to mechanical pressures, not to thermal
changes, not to any of the forces to which all the other organs of
our body are exposed; for nature has carefully shut up our brain and
spinal cord in bony boxes, where no influences of this sort can get at
them. She has floated them in fluid so that only the severest shocks
can give them a concussion, and blanketed and wrapped them about
in an altogether exceptional way. The only impressions that can be
made upon them are through the blood, on the one hand, and through
the sensory nerve-roots, on the other; and it is to the infinitely
attenuated currents that pour in through these latter channels that
the hemispherical cortex shows itself to be so peculiarly susceptible.
The currents, once in, must find a way out. In getting out they leave
their traces in the paths which they take. The only thing they _can_
do, in short, is to deepen old paths or to make new ones; and the whole
plasticity of the brain sums itself up in two words when we call it
an organ in which currents pouring in from the sense-organs make with
extreme facility paths which do not easily disappear. For, of course, a
simple habit, like every other nervous event--the habit of snuffling,
for example, or of putting one's hands into one's pockets, or of biting
one's nails--is, mechanically, nothing but a reflex discharge; and its
anatomical substratum must be a path in the system. The most complex
habits, as we shall presently see more fully, are, from the same point
of view, nothing but _concatenated_ discharges in the nerve-centres,
due to the presence there of systems of reflex paths, so organized as
to wake each other up successively--the impression produced by one
muscular contraction serving as a stimulus to provoke the next, until
a final impression inhibits the process and closes the chain. The only
difficult mechanical problem is to explain the formation _de novo_ of
a simple reflex or path in a pre-existing nervous system. Here, as in
so many other cases, it is only the _premier pas qui coûte_. For the
entire nervous system _is_ nothing but a system of paths between a
sensory _terminus a quo_ and a muscular, glandular, or other _terminus
ad quem_. A path once traversed by a nerve-current might be expected
to follow the law of most of the paths we know, and to be scooped out
and made more permeable than before;[139] and this ought to be repeated
with each new passage of the current. Whatever obstructions may have
kept it at first from being a path should then, little by little, and
more and more, be swept out of the way, until at last it might become
a natural drainage-channel. This is what happens where either solids
or liquids pass over a path; there seems no reason why it should not
happen where the thing that passes is a mere wave of rearrangement in
matter that does not displace itself, but merely changes chemically
or turns itself round in place, or vibrates across the line. The most
plausible views of the nerve-current make it out to be the passage
of some such wave of rearrangement as this. If only a part of the
matter of the path were to 'rearrange' itself, the neighboring parts
remaining inert, it is easy to see how their inertness might oppose
a friction which it would take many waves of rearrangement to break
down and overcome. If we call the path itself the 'organ,' and the
wave of rearrangement the 'function,' then it is obviously a case
for repeating the celebrated French formula of '_La fonction fait
l'organe._'

So nothing is easier than to imagine how, when a current once has
traversed a path, it should traverse it more readily still a second
time. But what made it ever traverse it the first time?[140] In
answering this question we can only fall back on our general conception
of a nervous system as a mass of matter whose parts, constantly kept
in states of different tension, are as constantly tending to equalize
their states. The equalization between any two points occurs through
whatever path may at the moment be most pervious. But, as a given point
of the system may belong, actually or potentially, to many different
paths, and, as the play of nutrition is subject to accidental changes,
_blocks_ may from time to time occur, and make currents shoot through
unwonted lines. Such an unwonted line would be a new-created path,
which if traversed repeatedly, would become the beginning of a new
reflex arc. All this is vague to the last degree, and amounts to little
more than saying that a new path may be formed by the sort of _chances_
that in nervous material are likely to occur. But, vague as it is, it
is really the last word of our wisdom in the matter.[141]

It must be noticed that the growth of structural modification in
living matter may be more rapid than in any lifeless mass, because the
incessant nutritive renovation of which the living matter is the seat
tends often to corroborate and fix the impressed modification, rather
than to counteract it by renewing the original constitution of the
tissue that has been impressed. Thus, we notice after exercising our
muscles or our brain in a new way, that we can do so no longer at that
time; but after a day or two of rest, when we resume the discipline,
our increase in skill not seldom surprises us. I have often noticed
this in learning a tune; and it has led a German author to say that we
learn to swim during the winter and to skate during the summer.

Dr. Carpenter writes:[142]

 "It is a matter of universal experience that every kind of training
 for special aptitudes is both far more effective, and leaves a more
 permanent impress, when exerted on the _growing_ organism than when
 brought to bear on the adult. The effect of such training is shown
 in the tendency of the organ to 'grow to' the mode in which it is
 habitually exercised; as is evidenced by the increased size and power
 of particular sets of muscles, and the extraordinary flexibility
 of joints, which are acquired by such as have been early exercised
 in gymnastic performances.... There is no part of the organism of
 man in which the _reconstructive activity_ is so great, during the
 whole period of life, as it is in the ganglionic substance of the
 brain. This is indicated by the enormous supply of blood which it
 receives.... It is, moreover, a fact of great significance that
 the nerve-substance is specially distinguished by its _reparative_
 power. For while injuries of other tissues (such as the muscular)
 which are distinguished by the _speciality_ of their structure and
 endowments, are repaired by substance of a lower or less specialized
 type, those of nerve-substance are repaired by a complete reproduction
 of the normal tissue; as is evidenced in the sensibility of the
 newly forming skin which is closing over an open wound, or in the
 recovery of the sensibility of a piece of 'transplanted' skin, which
 has for a time been rendered insensible by the complete interruption
 of the continuity of its nerves. The most remarkable example of
 this reproduction, however, is afforded by the results of M.
 Brown-Séquard's[143] experiments upon the gradual restoration of the
 functional activity of the spinal cord after its complete division;
 which takes place in a way that indicates rather a _reproduction_ of
 the whole, or the lower part of the cord and of the nerves proceeding
 from it, than a mere _reunion_ of divided surfaces. This reproduction
 is but a special manifestation of the reconstructive change which is
 _always_ taking place in the nervous system; it being not less obvious
 to the eye of reason that the 'waste' occasioned by its functional
 activity must be constantly repaired by the production of new tissue,
 than it is to the eye of sense that such reparation supplies an actual
 _loss_ of substance by disease or injury.

 "Now, in this constant and active reconstruction of the nervous
 system, we recognize a most marked conformity to the general plan
 manifested in the nutrition of the organism as a whole. For, in
 the first place, it is obvious that there is a tendency to the
 production of a _determinate type_ of structure; which type is often
 not merely that of the species, but some special modification of it
 which characterized one or both of the progenitors. But this type is
 peculiarly liable to modification during the early period of life; in
 which the functional activity of the nervous system (and particularly
 of the brain) is extraordinarily great, and the reconstructive process
 proportionally active. And this modifiability expresses itself in the
 formation of the mechanism by which those _secondarily automatic_
 modes of movement come to be established, which, in man, take the
 place of those that are _congenital_ in most of the animals beneath
 him; and those modes of sense-perception come to be _acquired_, which
 are elsewhere clearly _instinctive_. For there can be no reasonable
 doubt that, in both cases, a nervous mechanism is _developed_ in the
 course of this self-education, corresponding with that which the lower
 animals inherit from their parents. The _plan_ of that _rebuilding_
 process, which is necessary to maintain the integrity of the organism
 generally, and which goes on with peculiar activity in this portion of
 it, is thus being incessantly modified; and in this manner all that
 portion of it which ministers to the _external_ life of sense and
 motion that is shared by man with the animal kingdom at large, becomes
 at adult age the expression of the habits which the individual has
 acquired during the period of growth and development. Of these habits,
 some are common to the race generally, while others are peculiar to
 the individual; those of the former kind (such as walking erect) being
 universally acquired, save where physical inability prevents; while
 for the latter a special training is needed, which is usually the more
 effective the earlier it is begun--as is remarkably seen in the case
 of such feats of dexterity as require a conjoint education of the
 perceptive and of the motor powers. And when thus developed during
 the period of growth, so as to have become a part of the constitution
 of the adult, the acquired mechanism is thenceforth maintained in the
 ordinary course of the nutritive operations, so as to be ready for use
 when called upon, even after long inaction.

 "What is so clearly true of the nervous apparatus of animal life
 can scarcely be otherwise than true of that which ministers to the
 automatic activity of the mind. For, as already shown, the study
 of psychology has evolved no more certain result than that there
 are uniformities of mental action which are so entirely conformable
 to those of bodily action as to indicate their intimate relation
 to a 'mechanism of thought and feeling,' acting under the like
 conditions with that of sense and motion. The psychical principles
 of _association_, indeed, and the physiological principles of
 _nutrition_, simply express--the former in terms of mind, the latter
 in terms of brain--the universally admitted fact that any sequence of
 mental action which has been frequently repeated tends to perpetuate
 itself; so that we find ourselves automatically prompted to _think,
 feel,_ or _do_ what we have been before accustomed to think, feel,
 or do, under like circumstances, without any consciously formed
 _purpose_, or anticipation of results. For there is no reason to
 regard the cerebrum as an exception to the general principle that,
 while each part of the organism tends to _form itself_ in accordance
 with the mode in which it is habitually exercised, this tendency
 will be especially strong in the nervous apparatus, in virtue of
 that _incessant regeneration_ which is the very condition of its
 functional activity. It scarcely, indeed, admits of doubt that every
 state of ideational consciousness which is either _very strong_ or is
 _habitually repeated_ leaves an organic impression on the cerebrum; in
 virtue of which that same state may be reproduced at any future time,
 in respondence to a suggestion fitted to excite it.... The 'strength
 of early association' is a fact so universally recognized that the
 expression of it has become proverbial; and this precisely accords
 with the physiological principle that, during the period of growth
 and development, the formative activity of the brain will be most
 amenable to directing influences. It is in this way that what is early
 'learned by heart' becomes branded in (as it were) upon the cerebrum;
 so that its 'traces' are never lost, even though the conscious
 memory of it may have completely faded out. For, when the organic
 modification has been once _fixed_ in the growing brain, it becomes a
 part of the normal fabric, and is regularly _maintained_ by nutritive
 substitution; so that it may endure to the end of life, like the scar
 of a wound."

Dr. Carpenter's phrase that _our nervous system grows to the modes in
which it has been exercised_ expresses the philosophy of habit in a
nutshell. We may now trace some of the practical applications of the
principle to human life.

The first result of it is that _habit simplifies the movements required
to achieve a given result, makes them more accurate and diminishes
fatigue_.

 "The beginner at the piano not only moves his finger up and down in
 order to depress the key, he moves the whole hand, the forearm and
 even the entire body, especially moving its least rigid part, the
 head, as if he would press down the key with that organ too. Often
 a contraction of the abdominal muscles occurs as well. Principally,
 however, the impulse is determined to the motion of the hand and of
 the single finger. This is, in the first place, because the movement
 of the finger is the movement _thought of_ and, in the second place,
 because its movement and that of the key are the movements we try to
 _perceive_, along with the results of the latter on the ear. The more
 often the process is repeated, the more easily the movement follows,
 on account of the increase in permeability of the nerves engaged.

 "But the more easily the movement occurs, the slighter is the stimulus
 required to set it up; and the slighter the stimulus is, the more its
 effect is confined to the fingers alone.

 "Thus, an impulse which originally spread its effects over the whole
 body, or at least over many of its movable parts, is gradually
 determined to a single definite organ, in which it effects the
 contraction of a few limited muscles. In this change the thoughts and
 perceptions which start the impulse acquire more and more intimate
 causal relations with a particular group of motor nerves.

 "To recur to a simile, at least partially apt, imagine the nervous
 system to represent a drainage-system, inclining, on the whole, toward
 certain muscles, but with the escape thither somewhat clogged. Then
 streams of water will, on the whole, tend most to fill the drains
 that go towards these muscles and to wash out the escape. In case of
 a sudden 'flushing,' however, the whole system of channels will fill
 itself, and the water overflow everywhere before it escapes. But a
 moderate quantity of water invading the system will flow through the
 proper escape alone.

 "Just so with the piano-player. As soon as his impulse, which has
 gradually learned to confine itself to single muscles, grows extreme,
 it overflows into larger muscular regions. He usually plays with his
 fingers, his body being at rest. But no sooner does he get excited
 than his whole body becomes 'animated,' and he moves his head and
 trunk, in particular, as if these also were organs with which he meant
 to belabor the keys."[144]

Man is born with a tendency to do more things than he has ready-made
arrangements for in his nerve-centres. Most of the performances of
other animals are automatic. But in him the number of them is so
enormous, that most of them must be the fruit of painful study. If
practice did not make perfect, nor habit economize the expense of
nervous and muscular energy, he would therefore be in a sorry plight.
As Dr. Maudsley says:[145]

 "If an act became no easier after being done several times, if
 the careful direction of consciousness were necessary to its
 accomplishment on each occasion, it is evident that the whole activity
 of a lifetime might be confined to one or two deeds--that no progress
 could take place in development. A man might be occupied all day in
 dressing and undressing himself; the attitude of his body would
 absorb all his attention and energy; the washing of his hands or the
 fastening of a button would be as difficult to him on each occasion
 as to the child on its first trial; and he would, furthermore, be
 completely exhausted by his exertions. Think of the pains necessary to
 teach a child to stand, of the many efforts which it must make, and of
 the ease with which it at last stands, unconscious of any effort. For
 while secondarily automatic acts are accomplished with comparatively
 little weariness--in this regard approaching the organic movements, or
 the original reflex movements--the conscious effort of the will soon
 produces exhaustion. A spinal cord without ... memory would simply
 be an idiotic spinal cord.... It is impossible for an individual to
 realize how much he owes to its automatic agency until disease has
 impaired its functions."

The next result is that _habit diminishes the conscious attention with
which our acts are performed_.

One may state this abstractly thus: If an act require for its execution
a chain, _A, B, C, D, E, F, G,_ etc., of successive nervous events,
then in the first performances of the action the conscious will must
choose each of these events from a number of wrong alternatives that
tend to present themselves; but habit soon brings it about that each
event calls up its own appropriate successor without any alternative
offering itself, and without any reference to the conscious will,
until at last the whole chain, _A, B, C, D, E, F, G,_ rattles itself
off as soon as _A_ occurs, just as if _A_ and the rest of the chain
were fused into a continuous stream. When we are learning to walk,
to ride, to swim, skate, fence, write, play, or sing, we interrupt
ourselves at every step by unnecessary movements and false notes. When
we are proficients, on the contrary, the results not only follow with
the very minimum of muscular action requisite to bring them forth,
they also follow from a single instantaneous 'cue.' The marksman sees
the bird, and, before he knows it, he has aimed and shot. A gleam in
his adversary's eye, a momentary pressure from his rapier, and the
fencer finds that he has instantly made the right parry and return. A
glance at the musical hieroglyphics, and the pianist's fingers have
rippled through a cataract of notes. And not only is it the right
thing at the right time that we thus involuntarily do, but the wrong
thing also, if it be an habitual thing. Who is there that has never
wound up his watch on taking off his waistcoat in the daytime, or
taken his latch-key out on arriving at the door-step of a friend? Very
absent-minded persons in going to their bedroom to dress for dinner
have been known to take off one garment after another and finally to
get into bed, merely because that was the habitual issue of the first
few movements when performed at a later hour. The writer well remembers
how, on revisiting Paris after ten years' absence, and, finding himself