THE BRAIN

I

An animal deprived of the brain is a machine which requires external stimuli in order to move. An uninjured animal is also a machine, but it differs from the other by that power in itself which renders it capable of moving and acting.

When an animal with its brain removed is touched on any point of its body quite lightly, it does not respond at once to this external stimulus, and only when these light touches are often repeated is a reactionary movement excited. There are some very wonderful experiments which made a great impression on me, when I first saw them performed by my friends Kronecker and Stirling in the laboratory in Leipzig. They took a decapitated frog, and fastened between the toes of one of the hind-legs a pen, which made marks on the paper of a rotating cylinder whenever the frog moved. Between the toes of the other leg they fastened the wires of an electric current; a pendulum alternately opening and closing the current in such a manner that an interrupted stimulus was obtained. It was strange to see how the headless frog responded regularly for hours. When stimulated by a weak current (so weak that it could not be felt on the tongue) more numerous repetitions, perhaps thirty, were necessary before the frog responded by a spasmodic movement. If the stimulus were stronger a much smaller number was sufficient to cause reaction, and this continued until life was extinct.

Stimuli accumulate in the spinal cord. We all know it from experience; when we have something in the throat which tickles us, the slight, and at first scarcely perceptible, irritation becomes almost unbearable if it continues, compelling us to cough in order to remove it. As the Italian proverb says, one cannot disguise a cough. Even a slight tickling of the skin has the same effect, and in the functions of reproduction the repetition of slight stimuli produce greater and more ungovernable reflex movements.

There are, however, impressions which remain longer accumulated in the brain before their energy finds expression in muscular activity. Sometimes a part of the nervous system charges itself slowly, like a Leyden jar under the influence of weak electric sparks, the tension of the nerve-cells remaining, as it were, hidden, until suddenly discharged by a contact or some very slight impression. We are astonished; it seems an accidental explosion to us, an effect out of all proportion to the momentary cause, forgetting that fire glows under ashes, that the force had been slowly accumulating, and so we believe we have accomplished the act by means of the will.

The aptitude of the nerve-cells to accumulate and preserve external impressions is such a leading fact in physiology that I do not know any more important one.

If I were asked the difference between the brain and the spinal cord, I should say that the brain is more capable of accumulating impressions, not because of the difference of its substance, but because in it the nerve-cells serving this purpose are found in greater abundance.

The manner in which the brain has formed itself in the evolution of the animal world will render the comprehension of its activities easier. Let us consider the simplest creatures, those possessing, so to speak, only a spinal cord. The nerves branching off from the upper part to the nostrils, eyes, ears, mouth, and elsewhere, were subjected during the long series of generations to more continuous stimuli than other nerves. The cells placed at the roots of these nerves were constantly excited by impressions from the external world; chemical processes and combustion would be more rapid in them, hence the necessity of a more copious flow of blood to those parts which were in greater activity. These cells multiplied rapidly at the roots of the organs of sense, gradually covering a wider field. As the animal structure became more perfect during evolution, and the relations of the animal to the outer world increased, the more abundant and active the cells at the roots of these nerves would become. We must not think here of one individual, although individual exercise does strengthen an organ, but must fix our eyes on the interminable chain of generations, all working in this direction.

It was heredity (by which we still transmit to our children the structure and functions acquired by the nerve-centres) which, through the incessant efforts of our progenitors, enlarged this fertile field, until at last it resulted in the mass of the brain.

If, on visiting a museum of comparative anatomy, the reader will look into the glass cases set apart for the study of the nervous system, he will see that the lowest animals have only a spinal cord, or a very small protuberance at the place corresponding to the brain. As the animal structure becomes more complicated, there is a visible increase of the protuberance, which enlarges gradually the nearer one approaches the superior animals, until at last it reaches its maximum size in man.

II

One of the greatest experimenters of modern physiology, Flourens, had already given it as his opinion that the whole cerebral mass performs the same functions in all its parts, and that if one portion be taken away, those contiguous to it charge themselves with its offices. This affords a partial explanation of the fact that wounds of the brain are far less dangerous than those of the spinal cord. It is always a great wonder, even to us physiologists, every time we convince ourselves on living subjects that the brain is without feeling. Men have been seen who suffered great portions of their brain, which protruded from the skull, to be cut away, and sick drunkards or madmen, who, through the wounds in their head, seized hold of the brain with their hands and destroyed it.

Only in the last few years have physiologists succeeded in preserving alive for some time dogs of which nearly all the convolutions of the brain had been removed. Professor Goltz brought a dog in this state from Strasburg to London, in order to show the phenomena which an animal then presents, at the International Congress of Medicine. I extract a few fragments from Professor Goltz’s work,[9] in order to give an idea of the phenomena exhibited by dogs when deprived of a great part of their brain.

A brainless dog has a stupid, inane look. One reads idiocy even in his eyes. His movements are slow and uncertain. It seems as though he needed far more time than usual to come to a decision. His gait is like that of a goose, there is something inexpressibly strange and comical in it. The animal always walks straight on like an automaton. If he meets another dog, he steps over him if he is little; if he is big he may lift him with his head, or knock him down, but on he goes. He tries awkwardly to step over every object he meets, although by simply stepping aside he might pass on without hindrance. He only finds his dish of food with difficulty, smell guiding him better than sight; he snaps stupidly at everything he sees, even biting his own paws till he howls with pain. He can no longer find the fragments of bone that fall out of his mouth while chewing.

Dogs like these are no longer capable of learning anything, and one might almost say that they have forgotten what they already knew; for instance, they no longer give their paw to their master, as they used to do. Their whole intellectual life is extinguished; only when they hear a knock at the door do they bark, but they always begin too late. Two dogs that hated each other, bit each other when they met, even after both had lost a great part of their brain. Memory diminishes in proportion as larger quantities of the brain are removed, and disappears wholly when nearly the whole organ is wanting.

III

In order better to understand the working of the brain, we may divide it in imagination into two parts: a lower, situated at the base of the cerebral hemispheres, which forms the direct continuation of the spinal cord and is the centre of those movements which arise involuntarily during emotion; and another part in the upper story, as it were, which consists of the cerebral convolutions, is also in connection with the spinal cord, and must be considered as the seat of voluntary movement.

The enormous difference between the mind of a man and that of a child exists because in the latter the upper story of the brain is not developed, the convolutions are scarcely indicated, the organs of will and speech are wanting. As the large pyramidal cells appear and increase, the child acquires intelligence and speech; connections are established with the lower story in order to set muscles and organs which were before inactive into movement. But the difference between these two stories of nerve-centres continues during the whole life. I shall explain this by a few examples. A man is paralysed in consequence of some injury which prevents the upper story of his brain from communicating with the spinal cord. Hands and arms no longer move under the influence of the will, but when some long-expected person appears, or some sudden shock is given to the emotional sphere, he will be able to lift his arms. There is a paralysis of the facial nerve in which the voluntary closing of the eye is impossible, but if anyone makes a movement, as though he were going to poke his finger into the eye, the lid closes instantly. Later, we shall instance men who have remained dumb for a long time, and have regained their speech in consequence of a fright.

Dogs deprived of a large part of the upper story of the brain make no sign of recognition when they see themselves threatened by the whip, but if it is cracked they scamper off hurriedly, or rush forward at it. A mouse with its hemispheres and optic thalami removed remained undisturbed by every noise but that resembling an approaching cat, when it jumped and fled.

By means of injuries to the brain physiologists can easily check the activity of certain voluntary movements. If the peduncles of the cerebellum and certain points of the cerebrum are injured, dogs can be made to go either only to the right, or to the left, continually backwards, or in a circle, as though they were in a circus. The will of the animal is still in existence, but all his efforts are, as often with us, fruitless. In spite of himself his body is drawn in the direction determined by the lesion of the nerve-centres. Claude Bernard tells of a brave old general who, by a cruel irony of fate, could only march backwards.

Many physiologists have of late years tried to establish with precision the point of the brain which is the seat of emotional expressions; that is, that part, the destruction of which obliterates every expression of fear or pain in the animal, although allowing life to continue. One of the latest works published concerning this is by Bechterew. His observations show that a dog, in whose brain the corpora bigemina and quadrigemina have been destroyed, still barks and shows his teeth if anything loathsome is given him to eat, or if something smelling disagreeably is put before him; but that he is bereft of all expression of disgust and loathing after the two optic thalami have been removed. Hence Bechterew concludes that the paths of transmission along which pass the involuntary commands which cause the muscles to contract, in order to express the emotions, concentrate in the optic thalamus, which is one of the deepest parts of the brain. The upper story of volition and the lower of the emotions have here their point of union, whence to excite in the muscles of the organism all the characteristic movements of the passions.

IV

Let us now see what instinctive qualities we inherit from our forefathers, and what others we acquire through our own experience.

Long ago Galen performed a very simple and instructive experiment. He cut a kid out of the body of its mother, laid it immediately on the ground, and, near its head, dishes in which were oil, wine, honey, vinegar, water, and milk. He then stood to observe the first movements of the animal. After trembling a little, the kid got up, scratched itself, smelt a few of the dishes, and at last drank the milk.

There are birds which, scarcely out of the shell, catch flies with such precision that one is astonished at their bringing with them skill such as must usually be acquired by long practice. Certain butterflies, on leaving the cocoon, fly at once into the air, directing their flight with the most perfect accuracy towards the flowers, to suck the nectar from their cups.

We shall return to this point when we investigate fear in children. Let us here only state that, at his birth, man is far less perfect than many animals. He must acquire by education and experience much knowledge of which animals are possessed at the beginning.

The less care parents give to their young, the more completely do they furnish them through heredity with instinctive knowledge; the less considerable this inheritance, the more care and attention must parents give to their offspring in order to keep them alive.

This apparent inferiority in the gifts of instinct at birth is, as it is with the gifts of fortune, fully compensated for by the greater capability of those animals to increase their intellectual capacity by education, and by the work of their own experience to surpass by far animals more favoured by instinct; so it is with man, who subjugates them all.

Let us think of the tremendous difficulties which walking presents to man. Children are at first very much afraid of falling, even before they have experienced such a thing. Every movement is performed with difficulty; it is at first a task painfully learnt; gradually it becomes less a matter of reflection, until at last one can scarcely call it voluntary. We may not call it automatic, because when the will to make us walk is wanting we do not move, but when we have once set out on a walk, or to make a journey, we may go on for a long time without reflecting in the least that we are walking.

Ribot[10] tells of a violoncellist who suffered from epileptic vertigo, during which he became unconscious. He earned his living by playing in the orchestra of a theatre, and it was often noticed that he continued playing in time, even after he had lost consciousness. It has happened to all of us to read aloud without understanding what we have read, or absent-mindedly to write one word for another, and many will have experienced such extreme fatigue that they have slept while walking. There are endless phenomena proving that movements which at first cost a great effort of the will, become at length so habitual that we perform them without being aware of it.

Now what is the cause of this transformation of voluntary into automatic movements?

When we first try to execute a series of complicated movements the brain must work hard. If the cells of the upper story—that is, of the convolutions—do not take part in it, it all comes to nothing; the assistance of all the organs of sense is necessary in order to shed light on the confusion of orders and counterorders which must be sent to all the fibres of the muscles. The work is accomplished under the direction of a competent, enlightened administration; but through repetition of the same work, easier paths, broader lines of communication are formed in the lower story of the brain, and gradually the same work can be performed by the cells of the lower part—that is, without the co-operation of the will. This is easy to understand. The oftener a thing is repeated, the more the mechanism tends to become permanent, and it ends in the work being despatched by the less noble parts of the brain.

The serious aspect of the question is, that physiologists would like to catalogue many qualities which we have always considered as the most noble of our character, the most sublime feelings of human nature, amongst the automatic movements and more material instincts in the lower story of the brain.

For instance, for the maintenance of our species the love of the mother for her children is indispensable. The lower animals that produce a numerous offspring may carelessly abandon them, but when the progeny is sparse, there is no other way to preserve the species than through the greater and more prolonged attention on the part of the parents.

Let us for a moment study the character of the monkey. I quote from the celebrated book by Brehm, who conscientiously relates what he himself noticed.

'When the monkey-suckling is unable to do anything for itself, the mother is all the more gentle and tender with it. She occupies herself with it unceasingly, sometimes licking it, sometimes running after it or embracing it, looking at it as though revelling in the sight of it; then she lays it against her breast and rocks it to sleep. When the little monkey grows bigger the mother grants him a little freedom, but she never loses sight of him; she follows his every step and does not permit him to do everything he likes. She washes him in the brooks and smooths his fur with loving care.

'At the least danger she rushes to him with a cry, warning him to take refuge in her arms. Any disobedience is punished with pinches or cuffs, but this seldom happens, for the monkey does not do what its mother objects to. The death of the young one is, in many cases, followed by that of the mother from grief.[11] After a fight monkeys generally leave their wounded on the field; only the mothers defend their young against every enemy, however formidable. At first the mother tries to escape with the young one, but if she falls, she emits a loud cry of pain and remains still, in a threatening attitude, with wide-open mouth, gnashing her teeth, and menacing the enemy with outstretched arms.’

Davancel tells of the profound emotion he experienced after having killed a monkey. 'The poor animal had a young one with her, and the bullet hit her in the region of the heart. She made a last effort, placed the young one on the branch of a tree and then fell down dead. I have never felt,’ he says, 'greater remorse at having killed a creature, which, even in dying, showed feeling so worthy of admiration.’[12]

Whether this is instinct or affection, whether there is any difference between the love of man and of the monkey, I do not feel called upon to decide. I acknowledge that it is necessary for the maintenance of the species that things should be thus, nor need our admiration for mechanisms made in this way suffer any diminution.

I do not think I deserve praise for loving my mother. I remember what she did for me; and even if all our affection were only a simple automatic correspondence of instincts, if I knew that neither had the power to act otherwise, I should be just as glad to be constituted in such a manner that I cannot repress the throbbings of my heart whenever her face rises in my memory. I do not think that my tears and sorrow show less of love on that account.

And if I still feel myself drawn to the grave of the mother who died long years ago, thus cherishing her memory by visiting it in the greatest joys and sorrows of my life, I am glad to be an automaton feeling the religion of love in this renewal of the grief and tears of the last farewell.