The Principles of Psychology E-Book

William James

• Herausgeber: Andura Publishing
• Kategorie: Ratgeber
• Sprache: Englisch
• Veröffentlichungsjahr: 2020

Beschreibung

Experience the life-changing power of William James with this unforgettable book.

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Leseprobe

Principles of Psychology, Volume 1

by William James

TO

MY DEAR FRIEND

FRANÇOIS PILLON.

AS A TOKEN OF AFFECTION,

AND AN ACKNOWLEDGMENT OF WHAT I OWE

TO THE

CRITIQUE PHILOSOPHIQUE.

PREFACE.

The treatise which follows has in the main grown up in connection with

the author's class-room instruction in Psychology, although it is true

that some of the chapters are more 'metaphysical,' and others fuller of

detail, than is suitable for students who are going over the subject

for the first time. The consequence of this is that, in spite of the

exclusion of the important subjects of pleasure and pain, and moral and

æsthetic feelings and judgments, the work has grown to a length which

no one can regret more than the writer himself. The man must indeed be

sanguine who, in this crowded age, can hope to have many readers for

fourteen hundred continuous pages from his pen. But _wer Vieles bringt

wird Manchem etwas bringen_; and, by judiciously skipping according to

their several needs, I am sure that many sorts of readers, even those

who are just beginning the study of the subject, will find my book of

use. Since the beginners are most in need of guidance, I suggest for

their behoof that they omit altogether on a first reading chapters 6,

7, 8, 10 (from page 330 to page 371), 12, 13, 15, 17, 20, 21, and 28.

The better to awaken the neophyte's interest, it is possible that the

wise order would be to pass directly from chapter 4 to chapters 23, 24,

25, and 26, and thence to return to the first volume again. Chapter

20, on Space-perception, is a terrible thing, which, unless written

with all that detail, could not be fairly treated at all. An abridgment

of it, called 'The Spatial Quale,' which appeared in the Journal of

Speculative Philosophy, vol. xiii, p. 64, may be found by some persons

a useful substitute for the entire chapter.

I have kept close to the point of view of natural science throughout

the book. Every natural science assumes certain data uncritically, and

declines to challenge the elements between which its own 'laws' obtain,

and from which its own deductions are carried on. Psychology, the

science of finite individual minds, assumes as its data (1) _thoughts

and feelings_, and (2) _a physical world_ in time and space with which

they coexist and which (3) _they know_. Of course these data themselves

are discussable; but the discussion of them (as of other elements) is

called metaphysics and falls outside the province of this book. This

book, assuming that thoughts and feelings exist and are vehicles of

knowledge, thereupon contends that psychology when she has ascertained

the empirical correlation of the various sorts of thought or feeling

with definite conditions of the brain, can go no farther--can go

no farther, that is, as a natural science. If she goes farther she

becomes metaphysical. All attempts to _explain_ our phenomenally given

thoughts as products of deeper-lying entities (whether the latter be

named 'Soul,' 'Transcendental Ego,' 'Ideas,' or 'Elementary Units

of Consciousness') are metaphysical. This book consequently rejects

both the associationist and the spiritualist theories; and in this

strictly positivistic point of view consists the only feature of it

for which I feel tempted to claim originality. Of course this point of

view is anything but ultimate. Men must keep thinking; and the data

assumed by psychology, just like those assumed by physics and the other

natural sciences, must some time be overhauled. The effort to overhaul

them clearly and thoroughly is metaphysics; but metaphysics can only

perform her task well when distinctly conscious of its great extent.

Metaphysics fragmentary, irresponsible, and half-awake, and unconscious

that she is metaphysical, spoils two good things when she injects

herself into a natural science. And it seems to me that the theories

both of a spiritual agent and of associated 'ideas' are, as they figure

in the psychology-books, just such metaphysics as this. Even if their

results be true, it would be as well to keep them, _as thus presented_,

out of psychology as it is to keep the results of idealism out of

physics.

I have therefore treated our passing thoughts as integers, and

regarded the mere laws of their coexistence with brain-states as the

ultimate laws for our science. The reader will in vain seek for any

closed system in the book. It is mainly a mass of descriptive details,

running out into queries which only a metaphysics alive to the weight

of her task can hope successfully to deal with. That will perhaps be

centuries hence; and meanwhile the best mark of health that a science

can show is this unfinished-seeming front.

The completion of the book has been so slow that several chapters

have been published successively in Mind, the Journal of Speculative

Philosophy, the Popular Science Monthly, and Scribner's Magazine.

Acknowledgment is made in the proper places.

The bibliography, I regret to say, is quite unsystematic. I have

habitually given my authority for special experimental facts; but

beyond that I have aimed mainly to cite books that would probably

be actually used by the ordinary American college-student in his

collateral reading. The bibliography in W. Volkmann von Volkmar's

Lehrbuch der Psychologie (1875) is so complete, up to its date,

that there is no need of an inferior duplicate. And for more recent

references, Sully's Outlines, Dewey's Psychology, and Baldwin's

Handbook of Psychology may be advantageously used.

Finally, where one owes to so many, it seems absurd to single out

particular creditors; yet I cannot resist the temptation at the end of

my first literary venture to record my gratitude for the inspiration I

have got from the writings of J. S. Mill, Lotze, Renouvier, Hodgson,

and Wundt, and from the intellectual companionship (to name only five

names) of Chauncey Wright and Charles Peirce in old times, and more

recently of Stanley Hall, James Putnam, and Josiah Royce.

HARVARD UNIVERSITY, August 1890.

CONTENTS.

CHAPTER I.

THE SCOPE OF PSYCHOLOGY,

Mental Manifestations depend on Cerebral Conditions, 1. Pursuit of ends

and choice are the marks of Mind's presence.

CHAPTER II.

THE FUNCTIONS OF THE BRAIN

Reflex, semi-reflex, and voluntary acts. The Frog's nerve-centres.

General notion of the hemispheres. Their Education--the Meynert

scheme. The phrenological contrasted with the physiological

conception. The localization of function in the hemispheres.

The motor zone. Motor Aphasia. The sight-centre. Mental

blindness. The hearing-centre. Sensory Aphasia. Centres

for smell and taste. The touch-centre. Man's Consciousness

limited to the hemispheres. The restitution of function. Final

correction of the Meynert scheme. Conclusions.

CHAPTER III.

ON SOME GENERAL CONDITIONS OF BRAIN-ACTIVITY

The summation of Stimuli. Reaction-time. Cerebral blood-supply,

97. Cerebral Thermometry. Phosphorus and Thought.

CHAPTER IV.

HABIT

Due to plasticity of neural matter. Produces ease of action.

Diminishes attention, 115. Concatenated performances. Ethical

implications and pedagogic maxims.

CHAPTER V.

THE AUTOMATON-THEORY

The theory described. Reasons for it. Reasons against it.

CHAPTER VI.

THE MIND-STUFF THEORY

Evolutionary Psychology demands a Mind-dust. Some alleged proofs

that it exists. Refutation of these proofs. Self-compounding

of mental facts is inadmissible. Can states of mind be

unconscious? Refutation of alleged proofs of unconscious thought.

Difficulty of stating the connection between mind and brain.

'The Soul' is logically the least objectionable hypothesis.

Conclusion.

CHAPTER VII.

THE METHODS AND SNARES OF PSYCHOLOGY

Psychology is a natural Science. Introspection, 185. Experiment.

Sources of error. The 'Psychologist's fallacy'.

CHAPTER VIII.

THE RELATIONS OF MINDS TO OTHER THINGS

Time relations: lapses of Consciousness--Locke _v_. Descartes. The

'unconsciousness' of hysterics not genuine. Minds may split into

dissociated parts. Space-relations: the Seat of the Soul.

Cognitive relations. The Psychologist's point of view. Two

kinds of knowledge, acquaintance and knowledge about.

CHAPTER IX.

THE STREAM OF THOUGHT, 224

Consciousness tends to the personal form. It is in constant

change. It is sensibly continuous. 'Substantive' and

'transitive' parts of Consciousness. Feelings of relation.

Feelings of tendency. The 'fringe' of the object. The feeling

of rational sequence. Thought possible in any kind of mental

material. Thought and language. Consciousness is cognitive.

The word Object. Every cognition is due to one integral pulse

of thought. Diagrams of Thought's stream. Thought is always

selective.

CHAPTER X.

THE CONSCIOUSNESS OF SELF

The Empirical Self or Me. Its constituents. The material

self. The Social Self. The Spiritual Self. Difficulty of

apprehending Thought as a purely spiritual activity. Emotions of

Self. Rivalry and conflict of one's different selves. Their

hierarchy. What Self we love in 'Self-love'. The Pure Ego.

The verifiable ground of the sense of personal identity. The

passing Thought is the only Thinker which Psychology requires.

Theories of Self-consciousness: 1) The theory of the Soul. 2) The

Associationist theory. 3) The Transcendentalist theory. The

mutations of the Self. Insane delusions. Alternating selves.

Mediumships or possessions. Summary.

CHAPTER XI.

ATTENTION

Its neglect by English psychologists. Description of it.

To how many things can we attend at once? Wundt's experiments

on displacement of date of impressions simultaneously attended to.

Personal equation. The varieties of attention. Passive

attention. Voluntary attention. Attention's effects on

sensation;--on discrimination;--on recollection;--on

reaction-time. The neural process in attention: 1) Accommodation

of sense-organ. 2) Preperception. Is voluntary attention a

resultant or a force? The effort to attend can be conceived as a

resultant. Conclusion. Acquired Inattention.

CHAPTER XII.

CONCEPTION

The sense of sameness. Conception defined. Conceptions are

unchangeable. Abstract ideas, 468. Universals. The conception

'of the same' is not the 'same state' of mind.

CHAPTER XIII.

DISCRIMINATION AND COMPARISON

Locke on discrimination. Martineau _ditto_. Simultaneous

sensations originally fuse into one object. The principle of

mediate comparison. Not all differences are differences of

composition. The conditions of discrimination. The sensation

of difference. The transcendentalist theory of the perception

of differences uncalled for. The process of analysis. The

process of abstraction. The improvement of discrimination by

practice. Its two causes. Practical interests limit our

discrimination. Reaction-time after discrimination. The

perception of likeness, 528. The magnitude of differences. The

measurement of discriminative sensibility: Weber's law. Fechner's

interpretation of this as the psycho-physic law. Criticism

thereof.

CHAPTER XIV.

ASSOCIATION

The problem of the connection of our thoughts. It depends on

mechanical conditions. Association is of objects thought of,

not of 'ideas'. The rapidity of association. The 'law of

contiguity'. The elementary law of association. Impartial

redintegration. Ordinary or mixed association. The law of

interest. Association by similarity. Elementary expression of

the difference between the three kinds of association. Association

in voluntary thought. Similarity no elementary law. History

of the doctrine of association.

CHAPTER XV.

THE PERCEPTION OF TIME, 605

The sensible present. Its duration is the primitive

time-perception. Accuracy of our estimate of short durations.

We have no sense for empty time. Variations of our time-estimate.

The feeling of past time is a present feeling. Its cerebral

process.

CHAPTER XVI.

MEMORY

Primary memory. Analysis of the phenomenon of memory.

Retention and reproduction are both caused by paths of association

in the brain. The conditions of goodness in memory. Native

retentiveness is unchangeable. All improvement of memory consists

in better _thinking_. Other conditions of good memory.

Recognition, or the sense of familiarity. Exact measurements of

memory. Forgetting. Pathological cases. Professor Ladd

criticised.

INDEX.

PSYCHOLOGY.

CHAPTER I.

THE SCOPE OF PSYCHOLOGY.

Psychology is the Science of Mental Life, both of its phenomena

and of their conditions. The phenomena are such things as we call

feelings, desires, cognitions, reasonings, decisions, and the like;

and, superficially considered, their variety and complexity is such as

to leave a chaotic impression on the observer. The most natural and

consequently the earliest way of unifying the material was, first,

to classify it as well as might be, and, secondly, to affiliate the

diverse mental modes thus found, upon a simple entity, the personal

Soul, of which they are taken to be so many facultative manifestations.

Now, for instance, the Soul manifests its faculty of Memory, now of

Reasoning, now of Volition, or again its Imagination or its Appetite.

This is the orthodox 'spiritualistic' theory of scholasticism and of

common-sense. Another and a less obvious way of unifying the chaos is

to seek common elements in the divers mental facts rather than a common

agent behind them, and to explain them constructively by the various

forms of arrangement of these elements, as one explains houses by

stones and bricks. The 'associationist' schools of Herbart in Germany,

and of Hume the Mills and Bain in Britain have thus constructed a

_psychology without a soul_ by taking discrete 'ideas,' faint or

vivid, and showing how, by their cohesions, repulsions, and forms

of succession, such things as reminiscences, perceptions, emotions,

volitions, passions, theories, and all the other furnishings of an

individual's mind may be engendered. The very Self or _ego_ of the

individual comes in this way to be viewed no longer as the pre-existing

source of the representations, but rather as their last and most

complicated fruit.

Now, if we strive rigorously to simplify the phenomena in either of

these ways, we soon become aware of inadequacies in our method. Any

particular cognition, for example, or recollection, is accounted for

on the soul-theory by being referred to the spiritual faculties of

Cognition or of Memory. These faculties themselves are thought of as

absolute properties of the soul; that is, to take the case of memory,

no reason is given why we should remember a fact as it happened, except

that so to remember it constitutes the essence of our Recollective

Power. We may, as spiritualists, try to explain our memory's failures

and blunders by secondary causes. But its _successes_ can invoke no

factors save the existence of certain objective things to be remembered

on the one hand, and of our faculty of memory on the other. When,

for instance, I recall my graduation-day, and drag all its incidents

and emotions up from death's dateless night, no mechanical cause can

explain this process, nor can any analysis reduce it to lower terms or

make its nature seem other than an ultimate _datum_, which, whether we

rebel or not at its mysteriousness, must simply be taken for granted if

we are to psychologize at all. However the associationist may represent

the present ideas as thronging and arranging themselves, still, the

spiritualist insists, he has in the end to admit that _something_,

be it brain, be it 'ideas,' be it 'association,' _knows_ past time

_as_ past, and fills it out with this or that event. And when the

spiritualist calls memory an 'irreducible faculty,' he says no more

than this admission of the associationist already grants.

And yet the admission is far from being a satisfactory simplification

of the concrete facts. For why should this absolute god-given Faculty

retain so much better the events of yesterday than those of last

year, and, best of all, those of an hour ago? Why, again, in old

age should its grasp of childhood's events seem firmest? Why should

illness and exhaustion enfeeble it? Why should repeating an experience

strengthen our recollection of it? Why should drugs, fevers, asphyxia,

and excitement resuscitate things long since forgotten? If we content

ourselves with merely affirming that the faculty of memory is so

peculiarly constituted by nature as to exhibit just these oddities,

we seem little the better for having invoked it, for our explanation

becomes as complicated as that of the crude facts with which we

started. Moreover there is something grotesque and irrational in the

supposition that the soul is equipped with elementary powers of such an

ingeniously intricate sort. Why _should_ our memory cling more easily

to the near than the remote? Why should it lose its grasp of proper

sooner than of abstract names? Such peculiarities seem quite fantastic;

and might, for aught we can see _a priori_, be the precise opposites of

what they are. Evidently, then, _the faculty does not exist absolutely,

but works under conditions_; and _the quest of the conditions_ becomes

the psychologist's most interesting task.

However firmly he may hold to the soul and her remembering faculty, he

must acknowledge that she never exerts the latter without a _cue_, and

that something must always precede and _remind_ us of whatever we are

to recollect. "An _idea_," says the associationist, "an idea associated

with the remembered thing; and this explains also why things repeatedly

met with are more easily recollected, for their associates on the

various occasions furnish so many distinct avenues of recall." But this

does not explain the effects of fever, exhaustion, hypnotism, old age,

and the like. And in general, the pure associationist's account of our

mental life is almost as bewildering as that of the pure spiritualist.

This multitude of ideas, existing absolutely, yet clinging together,

and weaving an endless carpet of themselves, like dominoes in ceaseless

change, or the bits of glass in a kaleidoscope,--whence do they get

their fantastic laws of clinging, and why do they cling in just the

shapes they do?

For this the associationist must introduce the order of experience in

the outer world. The dance of the ideas is a copy, somewhat mutilated

and altered, of the order of phenomena. But the slightest reflection

shows that phenomena have absolutely no power to influence our ideas

until they have first impressed our senses and our brain. The bare

existence of a past fact is no ground for our remembering it. Unless

we have seen it, or somehow _undergone_ it, we shall never know of its

having been. The expediences of the body are thus one of the conditions

of the faculty of memory being what it is. And a very small amount

of reflection on facts shows that one part of the body, namely, the

brain, is the part whose experiences are directly concerned. If the

nervous communication be cut off between the brain and other parts,

the experiences of those other parts are non-existent for the mind.

The eye is blind, the ear deaf, the hand insensible and motionless.

And conversely, if the brain be injured, consciousness is abolished or

altered, even although every other organ in the body be ready to play

its normal part. A blow on the head, a sudden subtraction of blood, the

pressure of an apoplectic hemorrhage, may have the first effect; whilst

a very few ounces of alcohol or grains of opium or hasheesh, or a whiff

of chloroform or nitrous oxide gas, are sure to have the second. The

delirium of fever, the altered self of insanity, are all due to foreign

matters circulating through the brain, or to pathological changes in

that organ's substance. The fact that the brain is the one immediate

bodily condition of the mental operations is indeed so universally

admitted nowadays that I need spend no more time in illustrating it,

but will simply postulate it and pass on. The whole remainder of the

book will be more or less of a proof that the postulate was correct.

Bodily experiences, therefore, and more particularly brain-experiences,

must take a place amongst those conditions of the mental life of which

Psychology need take account. _The spiritualist and the associationist

must both be 'cerebralists'_, to the extent at least of admitting that

certain peculiarities in the way of working of their own favorite

principles are explicable only by the fact that the brain laws are a

codeterminant of the result. Our first conclusion, then, is that a

certain amount of brain-physiology must be presupposed or included in

Psychology.[1]

* * * * *

In still another way the psychologist is forced to be something of a

nerve-physiologist. Mental phenomena are not only conditioned _a parte

ante_ by bodily processes; but they lead to them _a parte post_. That

they lead to _acts_ is of course the most familiar of truths, but I do

not merely mean acts in the sense of voluntary and deliberate muscular

performances. Mental states occasion also changes in the calibre of

blood-vessels, or alteration in the heart-beats, or processes more

subtle still, in glands and viscera. If these are taken into account,

as well as acts which follow at some _remote period_ because the mental

state was once there, it will be safe to lay down the general law

that _no mental modification ever occurs which is not accompanied or

followed by a bodily change_. The ideas and feelings, _e.g_., which

these present printed characters excite in the reader's mind not only

occasion movements of his eyes and nascent movements of articulation in

him, but will some day make him speak, or take sides in a discussion,

or give advice, or choose a book to read, differently from what would

have been the case had they never impressed his retina. Our psychology

must therefore take account not only of the conditions antecedent to

mental states, but of their resultant consequences as well.

* * * * *

But actions originally prompted by conscious intelligence may grow

so automatic by dint of habit as to be apparently unconsciously

performed. Standing, walking, buttoning and unbuttoning, piano-playing,

talking, even saying one's prayers, may be done when the mind is

absorbed in other things. The performances of animal _instinct_ seem

semi-automatic, and the _reflex acts_ of self-preservation certainly

are so. Yet they resemble intelligent acts in bringing about the

_same ends_ at which the animals' consciousness, on other occasions,

deliberately aims. Shall the study of such machine-like yet purposive

acts as these be included in Psychology?

The boundary-line of the mental is certainly vague. It is better not

to be pedantic, but to let the science be as vague as its subject,

and include such phenomena as these if by so doing we can throw any

light on the main business in hand. It will ere long be seen, I trust,

that we can; and that we gain much more by a broad than by a narrow

conception of our subject. At a certain stage in the development

of every science a degree of vagueness is what best consists with

fertility. On the whole, few recent formulas have done more real

service of a rough sort in psychology than the Spencerian one that

the essence of mental life and of bodily life are one, namely, 'the

adjustment of inner to outer relations.' Such a formula is vagueness

incarnate; but because it takes into account the fact that minds

inhabit environments which act on them and on which they in turn

react; because, in short, it takes mind in the midst of all its

concrete relations, it is immensely more fertile than the old-fashioned

'rational psychology,' which treated the soul as a detached existent,

sufficient unto itself, and assumed to consider only its nature and

properties. I shall therefore feel free to make any sallies into

zoology or into pure nerve-physiology which may seem instructive

for our purposes, but otherwise shall leave those sciences to the

physiologists.

* * * * *

Can we state more distinctly still the manner in which the mental life

seems to intervene between impressions made from without upon the body,

and reactions of the body upon the outer world again? Let us look at a

few facts.

If some iron filings be sprinkled on a table and a magnet brought near

them, they will fly through the air for a certain distance and stick

to its surface. A savage seeing the phenomenon explains it as the

result of an attraction or love between the magnet and the filings.

But let a card cover the poles of the magnet, and the filings will

press forever against its surface without its ever occurring to them

to pass around its sides and thus come into more direct contact with

the object of their love. Blow bubbles through a tube into the bottom

of a pail of water, they will rise to the surface and mingle with the

air. Their action may again be poetically interpreted as due to a

longing to recombine with the mother-atmosphere above the surface. But

if you invert a jar full of water over the pail, they will rise and

remain lodged beneath its bottom, shut in from the outer air, although

a slight deflection from their course at the outset, or a re-descent

towards the rim of the jar when they found their upward course impeded,

would easily have set them free.

If now we pass from such actions as these to those of living things,

we notice a striking difference. Romeo wants Juliet as the filings

want the magnet; and if no obstacles intervene he moves towards her by

as straight a line as they. But Romeo and Juliet, if a wall be built

between them, do not remain idiotically pressing their faces against

its opposite sides like the magnet and the filings with the card. Romeo

soon finds a circuitous way, by scaling the wall or otherwise, of

touching Juliet's lips directly. With the filings the path is fixed;

whether it reaches the end depends on accidents. With the lover it is

the end which is fixed, the path may be modified indefinitely.

Suppose a living frog in the position in which we placed our bubbles

of air, namely, at the bottom of a jar of water. The want of breath

will soon make him also long to rejoin the mother-atmosphere, and he

will take the shortest path to his end by swimming straight upwards.

But if a jar full of water be inverted over him, he will not, like the

bubbles, perpetually press his nose against its unyielding roof, but

will restlessly explore the neighborhood until by re-descending again

he has discovered a path round its brim to the goal of his desires.

Again the fixed end, the varying means!

Such contrasts between living and inanimate performances end by leading

men to deny that in the physical world final purposes exist at all.

Loves and desires are to-day no longer imputed to particles of iron or

of air. No one supposes now that the end of any activity which they

may display is an ideal purpose presiding over the activity from its

outset and soliciting or drawing it into being by a sort of _vis a

fronte_. The end, on the contrary, is deemed a mere passive result,

pushed into being _a tergo_, having had, so to speak, no voice in its

own production. Alter the pre-existing conditions, and with inorganic

materials you bring forth each time a different apparent end. But

with intelligent agents, altering the conditions changes the activity

displayed, but not the end reached; for here the idea of the yet

unrealized end co-operates with the conditions to determine what the

activities shall be.

* * * * *

_The pursuance of future ends and the choice of means for their

attainment are thus the mark and criterion of the presence of

mentality_ in a phenomenon. We all use this test to discriminate

between an intelligent and a mechanical performance. We impute no

mentality to sticks and stones, because they never seem to move for

_the sake of_ anything, but always when pushed, and then indifferently

and with no sign of choice. So we unhesitatingly call them senseless.

Just so we form our decision upon the deepest of all philosophic

problems: Is the Kosmos an expression of intelligence rational in its

inward nature, or a brute external fact pure and simple? If we find

ourselves, in contemplating it, unable to banish the impression that it

is a realm of final purposes, that it exists for the sake of something,

we place intelligence at the heart of it and have a religion. If,

on the contrary, in surveying its irremediable flux, we can think

of the present only as so much mere mechanical sprouting from the

past, occurring with no reference to the future, we are atheists and

materialists.

In the lengthy discussions which psychologists have carried on about

the amount of intelligence displayed by lower mammals, or the amount

of consciousness involved in the functions of the nerve-centres of

reptiles, the same test has always been applied: Is the character of

the actions such that we must believe them to be performed _for the

sake_ of their result? The result in question, as we shall hereafter

abundantly see, is as a rule a useful one,--the animal is, on the

whole, safer under the circumstances for bringing it forth. So far

the action has a teleological character; but such mere outward

teleology as this might still be the blind result of _vis a tergo_.

The growth and movements of plants, the processes of development,

digestion, secretion, etc., in animals, supply innumerable instances

of performances useful to the individual which may nevertheless be,

and by most of us are supposed to be, produced by automatic mechanism.

The physiologist does not confidently assert conscious intelligence

in the frog's spinal cord until he has shown that the useful result

which the nervous machinery brings forth under a given irritation

_remains the same when the machinery is altered_. If, to take the stock

instance, the right knee of a headless frog be irritated with acid, the

right foot will wipe it off. When, however, this foot is amputated,

the animal will often raise the _left_ foot to the spot and wipe the

offending material away.

Pflüger and Lewes reason from such facts in the following way: If the

first reaction were the result of mere machinery, they say; if that

irritated portion of the skin discharged the right leg as a trigger

discharges its own barrel of a shot-gun; then amputating the right

foot would indeed frustrate the wiping, but would not make the _left_

leg move. It would simply result in the right stump moving through

the empty air (which is in fact the phenomenon sometimes observed).

The right trigger makes no effort to discharge the left barrel if the

right one be unloaded; nor does an electrical machine ever get restless

because it can only emit sparks, and not hem pillow-cases like a

sewing-machine.

If, on the contrary, the right leg originally moved for the _purpose_

of wiping the acid, then nothing is more natural than that, when the

easiest means of effecting that purpose prove fruitless, other means

should be tried. Every failure must keep the animal in a state of

disappointment which will lead to all sorts of new trials and devices;

and tranquillity will not ensue till one of these, by a happy stroke,

achieves the wished-for end.

In a similar way Goltz ascribes intelligence to the frog's optic

lobes and cerebellum. We alluded above to the manner in which a sound

frog imprisoned in water will discover an outlet to the atmosphere.

Goltz found that frogs deprived of their cerebral hemispheres would

often exhibit a like ingenuity. Such a frog, after rising from the

bottom and finding his farther upward progress checked by the glass

bell which has been inverted over him, will not persist in butting

his nose against the obstacle until dead of suffocation, but will

often re-descend and emerge from under its rim as if, not a definite

mechanical propulsion upwards, but rather a conscious desire to reach

the air by hook or crook were the main-spring of his activity. Goltz

concluded from this that the hemispheres are not the sole seal of

intellect in frogs. He made the same inference from observing that a

brainless frog will turn over from his back to his belly when one of

his legs is sewed up, although the movements required are then very

different from those excited under normal circumstances by the same

annoying position. They seem determined, consequently, not merely by

the antecedent irritant, but by the final end,--though the irritant of

course is what makes the end desired.

Another brilliant German author, Liebmann,[2] argues against the

brain's mechanism accounting for mental action, by very similar

considerations. A machine as such, he says, will bring forth right

results when it is in good order, and wrong results if out of repair.

But both kinds of result flow with equally fatal necessity from their

conditions. We cannot suppose the clock-work whose structure fatally

determines it to a certain rate of speed, noticing that this speed is

too slow or too fast and vainly trying to correct it. Its conscience,

if it have any, should be as good as that of the best chronometer, for

both alike obey equally well the same eternal mechanical laws--laws

from behind. But if the _brain_ be out of order and the man says "Twice

four are two," instead of "Twice four are eight," or else "I must go to

the coal to buy the wharf," instead of "I must go to the wharf to buy

the coal," instantly there arises a consciousness of error. The wrong

performance, though it obey the same mechanical law as the right, is

nevertheless condemned,--condemned as contradicting the inner law--the

law from in front, the purpose or ideal for which the brain _should_

act, whether it do so or not.

We need not discuss here whether these writers in drawing their

conclusion have done justice to all the premises I involved in the

cases they treat of. We quote their arguments only to show how they

appeal to the principle that _no actions but such as are done for an

end, and show a choice of means, can be called indubitable expressions

of Mind_.

I shall then adopt this as the criterion by which to circumscribe the

subject-matter of this work so far as action enters into it. Many

nervous performances will therefore be unmentioned, as being purely

physiological. Nor will the anatomy of the nervous system and organs of

sense be described anew. The reader will find in H. N. Martin's 'Human

Body,' in G. T. Ladd's 'Physiological Psychology,' and in all the other

standard Anatomies and Physiologies, a mass of information which we

must regard as preliminary and take for granted in the present work.[3]

Of the functions of the cerebral hemispheres, however, since they

directly subserve consciousness, it will be well to give some little

account.

FOOTNOTES:

[1] _Cf._ Geo. T. Ladd: Elements of Physiological Psychology (1887),

pt. iii, chap. iii, §§ 9, 12.

[2] Zur Analysis der Wirklichkeit, p. 489.

[3] Nothing is easier than to familiarize one's self with the mammalian

brain. Get a sheep's head, a small saw, chisel, scalpel and forceps

(all three can best be had from a surgical-instrument maker), and

unravel its parts either by the aid of a human dissecting book, such as

Holden's 'Manual of Anatomy,' or by the specific directions _ad hoc_

given in such books as Foster and Langley's 'Practical Physiology'

(Macmillan) or Morrell's 'Comparative Anatomy and Dissection of

Mammalia' (Longmans).

CHAPTER II.

THE FUNCTIONS OF THE BRAIN.

If I begin chopping the foot of a tree, its branches are unmoved by my

act, and its leaves murmur as peacefully as ever in the wind. If, on

the contrary, I do violence to the foot of a fellow-man, the rest of

his body instantly responds to the aggression by movements of alarm or

defence. The reason of this difference is that the man has a nervous

system whilst the tree has none; and the function of the nervous system

is to bring each part into harmonious co-operation with every other.

The afferent nerves, when excited by some physical irritant, be this

as gross in its mode of operation as a chopping axe or as subtle as

the waves of light, conveys the excitement to the nervous centres. The

commotion set up in the centres does not stop there, but discharges

itself, if at all strong, through the efferent nerves into muscles

and glands, exciting movements of the limbs and viscera, or acts of

secretion, which vary with the animal, and with the irritant applied.

These acts of response have usually the common character of being of

service. They ward off the noxious stimulus and support the beneficial

one; whilst if, in itself indifferent, the stimulus be a sign of some

distant circumstance of practical importance, the animal's acts are

addressed to this circumstance so as to avoid its perils or secure its

benefits, as the case may be. To take a common example, if I hear the

conductor calling 'All aboard!' as I enter the depot, my heart first

stops, then palpitates, and my legs respond to the air-waves falling

on my tympanum by quickening their movements. If I stumble as I run,

the sensation of falling provokes a movement of the hands towards the

direction of the fall, the effect of which is to shield the body from

too sudden a shock. If a cinder enter my eye, its lids close forcibly

and a copious flow of tears tends to wash it out.

These three responses to a sensational stimulus differ, however, in

many respects. The closure of the eye and the lachrymation are quite

involuntary, and so is the disturbance of the heart. Such involuntary

responses we know as 'reflex' acts. The motion of the arms to break the

shock of falling may also be called reflex, since it occurs too quickly

to be deliberately intended. Whether it be instinctive or whether it

result from the pedestrian education of childhood may be doubtful; it

is, at any rate, less automatic than the previous acts, for a man might

by conscious effort learn to perform it more skilfully, or even to

suppress it altogether. Actions of this kind, into which instinct and

volition enter upon equal terms, have been called 'semi-reflex.' The

act of running towards the train, on the other hand, has no instinctive

element about it. It is purely the result of education, and is preceded

by a consciousness of the purpose to be attained and a distinct mandate

of the will. It is a 'voluntary act.' Thus the animal's reflex and

voluntary performances shade into each other gradually, being connected

by acts which may often occur automatically, but may also be modified

by conscious intelligence.

An outside observer, unable to perceive the accompanying consciousness,

might be wholly at a loss to discriminate between the automatic acts

and those which volition escorted. But if the criterion of mind's

existence be the choice of the proper means for the attainment of a

supposed end, all the acts seem to be inspired by intelligence, for

_appropriateness_ characterizes them all alike. This fact, now, has led

to two quite opposite theories about the relation to consciousness of

the nervous functions. Some authors, finding that the higher voluntary

ones seem to require the guidance of feeling, conclude that over the

lowest reflexes some such feeling also presides, though it may be a

feeling of which _we_ remain unconscious. Others, finding that reflex

and semi-automatic acts may, notwithstanding their appropriateness,

take place with an unconsciousness apparently complete, fly to the

opposite extreme and maintain that the appropriateness even of

voluntary actions owes nothing to the fact that consciousness attends

them. They are, according to these writers, results of physiological

mechanism pure and simple. In a near chapter we shall return to this

controversy again. Let us now look a little more closely at the brain

and at the ways in which its states may be supposed to condition those

of the mind.

THE FROG'S NERVE-CENTRES.

Both the minute anatomy and the detailed physiology of the brain are

achievements of the present generation, or rather we may say (beginning

with Meynert) of the past twenty years. Many points are still obscure

and subject to controversy; but a general way of conceiving the organ

has been reached on all hands which in its main feature seems not

unlikely to stand, and which even gives a most plausible scheme of the

way in which cerebral and mental operations go hand in hand.

[Illustration: FIG. 1.--_C H_, cerebral Hemispheres; _O Th_, Optic

Thalami; _O L_, Optic Lobes; _Cb_, Cerebellum; _M O_, Medulla

Oblongata; _S C_, Spinal cord.]

The best way to enter the subject will be to take a lower creature,

like a frog, and study by the vivisectional method the functions of

his different nerve-centres. The frog's nerve-centres are figured

in the accompanying diagram, which needs no further explanation. I

will first proceed to state what happens when various amounts of the

anterior parts are removed, in different frogs, in the way in which an

ordinary student removes them; that is, with no extreme precautions

as to the purity of the operation. We shall in this way reach a very

simple conception of the functions of the various centres, involving

the strongest possible contrast between the cerebral hemispheres and

the lower lobes. This sharp conception will have didactic advantages,

for it is often very instructive to start with too simple a formula

and correct it later on. Our first formula, as we shall later see,

will have to be softened down somewhat by the results of more careful

experimentation both on frogs and birds, and by those of the most

recent observations on dogs, monkeys, and man. But it will put us,

from the outset, in clear possession of some fundamental notions and

distinctions which we could otherwise not gain so well, and none of

which the later more completed view will overturn.

If, then, we reduce the frog's nervous system to the spinal cord

alone, by making a section behind the base of the skull, between the

spinal cord and the medulla oblongata, thereby cutting off the brain

from all connection with the rest of the body, the frog will still

continue to live, but with a very peculiarly modified activity. It

ceases to breathe or swallow; it lies flat on its belly, and does not,

like a normal frog, sit up on its fore paws, though its hind legs

are kept, as usual, folded against its body and immediately resume

this position if drawn out. If thrown on its back, it lies there

quietly, without turning over like a normal frog. Locomotion and voice

seem entirely abolished. If we suspend it by the nose, and irritate

different portions of its skin by acid, it performs a set of remarkable

'defensive' movements calculated to wipe away the irritant. Thus, if

the breast be touched, both fore paws will rub it vigorously; if we

touch the outer side of the elbow, the hind foot of the same side

will rise directly to the spot and wipe it. The back of the foot will

rub the knee if that be attacked, whilst if the foot be cut away, the

stump will make ineffectual movements, and then, in many frogs, a pause

will come, as if for deliberation, succeeded by a rapid passage of the

opposite unmutilated foot to the acidulated spot.

The most striking character of all these movements, after their

teleological appropriateness, is their precision. They vary, in

sensitive frogs and with a proper amount of irritation, so little as

almost to resemble in their machine-like regularity the performances of

a jumping-jack, whose legs must twitch whenever you pull the string.

The spinal cord of the frog thus contains arrangements of cells and

fibres fitted to convert skin irritations into movements of defence. We

may call it the _centre for defensive movements_ in this animal. We may

indeed go farther than this, and by cutting the spinal cord in various

places find that its separate segments are independent mechanisms,

for appropriate activities of the head and of the arms and legs

respectively. The segment governing the arms is especially active,

in male frogs, in the breeding season; and these members alone with

the breast and back appertaining to them, everything else being cut

away, will then actively grasp a finger placed between them and remain

hanging to it for a considerable time.

The spinal cord in other animals has analogous powers. Even in man

it makes movements of defence. Paraplegics draw up their legs when

tickled; and Robin, on tickling the breast of a criminal an hour after

decapitation, saw the arm and hand move towards the spot. Of the lower

functions of the mammalian cord, studied so ably by Goltz and others,

this is not the place to speak.

If, in a second animal, the cut be made just behind the optic lobes so

that the cerebellum and medulla oblongata remain attached to the cord,

then swallowing, breathing, crawling, and a rather enfeebled jumping

and swimming are added to the movements previously observed.[4] There

are other reflexes too. The animal, thrown on his back, immediately

turns over to his belly. Placed in a shallow bowl, which is floated on

water and made to rotate, he responds to the rotation by first turning

his head and then waltzing around with his entire body, in the opposite

direction to the whirling of the bowl. If his support be tilted so that

his head points downwards, he points it up; he points it down if it be

pointed upwards, to the right if it be pointed to the left, etc. But

his reactions do not go farther than these movements of the head. He

will not, like frogs whose thalami are preserved, climb up a board if

the latter be tilted, but will slide off it to the ground.

If the cut be made on another frog between the thalami and the optic

lobes, the locomotion both on land and water becomes quite normal, and,

in addition to the reflexes already shown by the lower centres, he

croaks regularly whenever he is pinched under the arms. He compensates

rotations, etc., by movements of the head, and turns over from his

back; but still drops off his tilted board. As his optic nerves are

destroyed by the usual operation, it is impossible to say whether he

will avoid obstacles placed in his path.

When, finally, a frog's cerebral hemispheres alone are cut off by a

section between them and the thalami which preserves the latter, an

unpractised observer would not at first suspect anything abnormal

about the animal. Not only is he capable, on proper instigation, of

all the acts already described, but he guides himself by sight, so

that if an obstacle be set up between him and the light, and he be

forced to move forward, he either jumps over it or swerves to one

side. He manifests sexual passion at the proper season, and, unlike an

altogether brainless frog, which embraces anything placed between his

arms, postpones this reflex act until a female of his own species is

provided. Thus far, as aforesaid, a person unfamiliar with frogs might

not suspect a mutilation; but even such a person would soon remark the

almost entire absence of spontaneous motion--that is, motion unprovoked

by any _present_ incitation of sense. The continued movements of

swimming, performed by the creature in the water, seem to be the fatal

result of the contact of that fluid with its skin. They cease when a

stick, for example, touches his hands. This is a sensible irritant

towards which the feet are automatically drawn by reflex action, and

on which the animal remains sitting. He manifests no hunger, and will

suffer a fly to crawl over his nose unsnapped at. Fear, too, seems

to have deserted him. In a word, he is an extremely complex machine

whose actions, so far as they go, tend to self-preservation; but still

a _machine_, in this sense--that it seems to contain no incalculable

element. By applying the right sensory stimulus to him we are almost

as certain of getting a fixed response as an organist is of hearing a

certain tone when he pulls out a certain stop.

But now if to the lower centres we add the cerebral hemispheres,

or if, in other words, we make an intact animal the subject of our

observations, all this is changed. In addition to the previous

responses to present incitements of sense, our frog now goes through

long and complex acts of locomotion _spontaneously_, or as if moved by

what in ourselves we should call an idea. His reactions to outward

stimuli vary their form, too. Instead of making simple defensive

movements with his hind legs like a headless frog if touched, or of

giving one or two leaps and then sitting still like a hemisphereless

one, he makes persistent and varied efforts at escape, as if, not the

mere contact of the physiologist's hand, but the notion of danger

suggested by it were now his spur. Led by the feeling of hunger, too,

he goes in search of insects, fish, or smaller frogs, and varies his

procedure with each species of victim. The physiologist cannot by

manipulating him elicit croaking, crawling up a board, swimming or

stopping, at will. His conduct has become incalculable. We can no

longer foretell it exactly. Effort to escape is his dominant reaction,

but he _may_ do anything else, even swell up and become perfectly

passive in our hands.

* * * * *

Such are the phenomena commonly observed, and such the impressions

which one naturally receives. Certain general conclusions follow

irresistibly. First of all the following:

_The acts of all the centres involve the use of the same muscles._ When

a headless frog's hind leg wipes the acid, he calls into play all the

leg-muscles which a frog with his full medulla oblongata and cerebellum

uses when he turns from his back to his belly. Their contractions are,

however, _combined_ differently in the two cases, so that the results

vary widely. We must consequently conclude that specific arrangements

of cells and fibres exist in the cord for wiping, in the medulla for

turning over, etc. Similarly they exist in the thalami for jumping

over seen obstacles and for balancing the moved body; in the optic

lobes for creeping backwards, or what not. But in the hemispheres,

since the presence of these organs _brings no new elementary form of

movement_ with it, but only _determines differently the occasions_

on which the movements shall occur, making the usual stimuli less

fatal and machine-like; we need suppose no such machinery _directly_

co-ordinative of muscular contractions to exist. We may rather

assume, when the mandate for a wiping-movement is sent forth by the

hemispheres, that a current goes straight to the wiping-arrangement in

the spinal cord, exciting this arrangement as a whole. Similarly, if an

intact frog wishes to jump over a stone which he sees, all he need do

is to excite from the hemispheres the jumping-centre in the thalami or

wherever it may be, and the latter will provide for the details of the

execution. It is like a general ordering a colonel to make a certain

movement, but not telling him how it shall be done.[5]

_The same muscle, then, is repeatedly represented at different

heights;_ and at each it enters into a different combination with other

muscles to co-operate in some special form of concerted movement.

_At each height the movement is discharged by some particular form

of sensorial stimulus._ Thus in the cord, the skin alone occasions

movements; in the upper part of the optic lobes, the eyes are added;

in the thalami, the semi-circular canals would seem to play a part;

whilst the stimuli which discharge the hemispheres would seem not so

much to be elementary sorts of sensation, as groups of sensations

forming determinate _objects_ or _things. Prey_ is not pursued nor are

_enemies_ shunned by ordinary hemisphereless frogs. Those reactions

upon complex circumstances which we call instinctive rather than

reflex, are already in this animal dependent on the brain's highest

lobes, and still more is this the case with animals higher in the

zoological scale.

The results are just the same if, instead of a frog, we take a pigeon,

and cut out his hemispheres as they are ordinarily cut out for a

lecture-room demonstration. There is not a movement natural to him

which this brainless bird cannot perform if expressly excited thereto;

only the inner promptings seem deficient, and when left to himself

he spends most of his time crouched on the ground with his head sunk

between his shoulders as if asleep.

GENERAL NOTION OF HEMISPHERES.

All these facts lead us, when we think about them, to some such

explanatory conception as this: _The lower centres act from present

sensational stimuli alone; the hemispheres act from perceptions and

considerations,_ the sensations which they may receive serving only as

suggesters of these. But what are perceptions but sensations grouped

together? and what are considerations but expectations, in the fancy,

of sensations which will be felt one way or another according as action

takes this course or that? If I step aside on seeing a rattlesnake,

from considering how dangerous an animal he is, the mental materials

which constitute my prudential reflection are images more or less vivid

of the movement of his head, of a sudden pain in my leg, of a state of

terror, a swelling of the limb, a chill, delirium, unconsciousness,

etc., etc., and the ruin of my hopes. But all these images are

constructed out of my past experiences. They are _reproductions_ of

what I have felt or witnessed. They are, in short, _remote_ sensations;

and the _difference between the hemisphereless animal and the whole

one_ may be concisely expressed by saying that the _one obeys absent,

the other only present, objects._

The hemispheres would then seem to be _the seat of memory_. Vestiges

of past experience must in some way be stored up in them, and must,

when aroused by present stimuli, first appear as representations of

distant goods and evils; and then must discharge into the appropriate

motor channels for warding off the evil and securing the benefits of

the good. If we liken the nervous currents to electric currents, we

can compare the nervous system, _C_, below the hemispheres to a direct

circuit from sense-organ to muscle along the line _S ... C ... M_ of

Fig. 2. The hemisphere, _H_, adds the long circuit or loop-line through

which the current may pass when for any reason the direct line is not

used.

Thus, a tired wayfarer on a hot day throws himself on the damp earth

beneath a maple-tree. The sensations of delicious rest and coolness

pouring themselves through the direct line would naturally discharge

into the muscles of complete extension: he would abandon himself

to the dangerous repose. But the loop-line being open, part of the

current is drafted along it, and awakens rheumatic or catarrhal

reminiscences, which prevail over the instigations of sense, and

make the man arise and pursue his way to where he may enjoy his rest

more safely. Presently we shall examine the manner in which the

hemispheric loop-line may be supposed to serve as a reservoir for such

reminiscences as these. Meanwhile I will ask the reader to notice some

corollaries of its being such a reservoir.

[Illustration: FIG. 2.]

First, no animal without it can deliberate, pause, postpone, nicely

weigh one motive against another, or compare. Prudence, in a word,

is for such a creature an impossible virtue. Accordingly we see that

nature removes those functions in the exercise of which prudence is

a virtue from the lower centres and hands them over to the cerebrum.

Wherever a creature has to deal with complex features of the

environment, prudence is a virtue. The higher animals have so to deal;

and the more complex the features, the higher we call the animals. The

fewer of his acts, then, can _such_ an animal perform without the help

of the organs in question. In the frog many acts devolve wholly on the

lower centres; in the bird fewer; in the rodent fewer still; in the dog

very few indeed; and in apes and men hardly any at all.

The advantages of this are obvious. Take the prehension of food as an

example and suppose it to be a reflex performance of the lower centres.

The animal will be condemned fatally and irresistibly to snap at it

whenever presented, no matter what the circumstances may be; he can no

more disobey this prompting than water can refuse to boil when a fire

is kindled under the pot. His life will again and again pay the forfeit

of his gluttony. Exposure to retaliation, to other enemies, to traps,

to poisons, to the dangers of repletion, must be regular parts of his

existence. His lack of all thought by which to weigh the danger against

the attractiveness of the bait, and of all volition to remain hungry

a little while longer, is the direct measure of his lowness in the

mental scale. And those fishes which, like our cunners and sculpins,

are no sooner thrown back from the hook into the water, than they

automatically seize the hook again, would soon expiate the degradation

of their intelligence by the extinction of their type, did not their

exaggerated fecundity atone for their imprudence. Appetite and the acts

it prompts have consequently become in all higher vertebrates functions

of the cerebrum. They disappear when the physiologist's knife has left

the subordinate centres alone in place. The brainless pigeon will

starve though left on a corn-heap.

Take again the sexual function. In birds this devolves exclusively

upon the hemispheres. When these are shorn away the pigeon pays no

attention to the billings and cooings of its mate. And Goltz found that

a bitch in heat would excite no emotion in male dogs who had suffered

large loss of cerebral tissue. Those who have read Darwin's 'Descent of

Man' know what immense importance in the amelioration of the breed in

birds this author ascribes to the mere fact of sexual selection. The

sexual act is not performed until every condition of circumstance and

sentiment is fulfilled, until time, place, and partner all are fit. But

in frogs and toads this passion devolves on the lower centres. They

show consequently a machine-like obedience to the present incitement of

sense, and an almost total exclusion of the power of choice. Copulation

occurs _per fas aut nefas_, occasionally between males, often with dead

females, in puddles exposed on the highway, and the male may be cut in

two without letting go his hold. Every spring an immense sacrifice of

batrachian life takes place from these causes alone.

No one need be told how dependent all human social elevation is upon

the prevalence of chastity. Hardly any factor measures more than this

the difference between civilisation and barbarism. Physiologically

interpreted, chastity means nothing more than the fact that present

solicitations of sense are overpowered by suggestions of æsthetic and

moral fitness which the circumstances awaken in the cerebrum; and that

upon the inhibitory or permissive influence of these alone action

directly depends.

Within the psychic life due to the cerebrum itself the same general

distinction obtains, between considerations of the more immediate

and considerations of the more remote. In all ages the man whose

determinations are swayed by reference to the most distant ends has

been held to possess the highest intelligence. The tramp who lives

from hour to hour; the bohemian whose engagements are from day to day;

the bachelor who builds but for a single life; the father who acts

for another generation; the patriot who thinks of a whole community

and many generations; and finally, the philosopher and saint whose

cares are for humanity and for eternity,--these range themselves in

an unbroken hierarchy, wherein each successive grade results from an

increased manifestation of the special form of action by which the

cerebral centres are distinguished from all below them.

In the 'loop-line' along which the memories and ideas of the distant

are supposed to lie, the action, so far as it is a physical process,

must be interpreted after the type of the action in the lower centres.

If regarded here as a reflex process, it must be reflex there as

well. The current in both places runs out into the muscles only after

it has first run in; but whilst the path by which it runs out is

determined in the lower centres by reflections few and fixed amongst

the cell-arrangements, in the hemispheres the reflections are many and

instable. This, it will be seen, is only a difference of degree and not

of kind, and does not change the reflex type. The conception of _all_

action as conforming to this type is the fundamental conception of

modern nerve-physiology. So much for our general preliminary conception

of the nerve-centres! Let us define it more distinctly before we see

how well physiological observation will bear it out in detail.

THE EDUCATION OF THE HEMISPHERES.

Nerve-currents run in through sense-organs, and whilst provoking reflex

acts in the lower centres, they arouse ideas in the hemispheres, which

either permit the reflexes in question, check them, or substitute

others for them. All ideas being in the last resort reminiscences,

the question to answer is: _How can processes become organized in the

hemispheres which correspond to reminiscences in the mind?_[6]

Nothing is easier than to conceive a _possible_ way in which this might

be done, provided four assumptions be granted. These assumptions (which

after all are inevitable in any event) are:

1) The same cerebral process which, when aroused from without by a

sense-organ, gives the perception of an object, will give an _idea_ of

the same object when aroused by other cerebral processes from within.

2) If processes 1, 2, 3, 4 have once been aroused together or in

immediate succession, any subsequent arousal of any one of them

(whether from without or within) will tend to arouse the others in the

original order. [This is the so-called law of association.]

3) Every sensorial excitement propagated to a lower centre tends to