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._'