There is no remedy. He who wishes to explain a scientific subject in a clear and simple way must stop from time to time; he must come out of himself and take his reader’s place, forget all he knows in order to listen impartially to his own voice, and to judge if what he has said may be easily understood. And this I shall do, but the reader must not be repulsed by the first difficulties: our first steps cost the greatest effort. In order to comprehend the physical nature of man, and to know how this exquisite machinery of ours works, we must first examine attentively some of the most important organs which are constantly at work in our nervous system. It is in science as in the study of languages, one must first learn the meaning of the most indispensable words in order to understand what is said to us in the foreign tongue.
Till the beginning of this century very confused notions prevailed as to the activity of the brain and spinal cord. Luigi Rolando, the celebrated physiologist of the University of Turin, was the first who clearly showed that the medulla oblongata (that part of the spinal cord which lies nearest the brain) must be regarded as the centre of the whole nervous system. No one in his time knew the structure of the nerve-centres better than he, and it was he who proved that the medulla oblongata 'is the first rudiment of the nervous system, the seat of physical sensibility, of instinct, the director of voluntary movements, the centre of life, and the wonderful cause of most surprising phenomena known under the names of sympathies and consents.’[7]
If one cuts the head of a duck off at a blow, it does not remain motionless but moves, flaps its wings and flutters along, as though it meant to make its escape. It is said that the Emperor Commodus caused the heads of the ostriches in the circus to be shot off with curved arrows, and that the birds still ran on till they reached the goal. If we cut the head of a dog off with a hatchet, we see that the trunk wags the tail. There is a curious irony in the fact, but it need not shock us, for the animal no longer feels. If an irritant is applied to the skin, it draws its tail between its legs as though it were afraid, although it is headless.
V
A difficult question confronts us here. There are some physiologists who maintain that the maid is blind, and that she performs her work without knowing what she does; that she pulls the cord when the bell rings, heats the stoves, cooks, cleans the utensils, sweeps the house, gives the rubbish to the dustman, and so on—but all this without power of discernment, acting like an automaton, unable to make the slightest change in what she does merely from habit. Others, again, maintain that she does possess a few fragments of intelligence, that at certain times she reasons too, and that the soul of the house does not dwell in the master alone.
It is a very difficult question; because, if it can be proved that the maid is blind and does everything from habit, one may also say that the master—poor man!—does not see much either, and that he has certainly not been able to teach the maid anything.
I say the question is difficult also because the names of the greatest living physiologists are connected with it. Goltz and Foster took a frog, destroyed its brain, and then plunged it into a vessel full of water. If the frog were then touched it might be seen, like other frogs in similar circumstances, to respond by swimming about and even jumping out of the vessel. The water was then warmed up to 40°. The frog remained motionless, nor did it feel that the water was growing hot; it did not try to leap out, and thus allowed the heat to increase until it was boiled without making any movement which might indicate sensation. Therefore the spinal cord alone cannot think. The frog moves like a machine whenever it feels those stimuli to which it is accustomed (like an automaton of which one must press a certain knob in order to produce a particular movement); it is indifferent to everything else, allowing itself to be burnt and boiled and never moving, because no pain is felt.
My friend Tiegel, professor of physiology in Japan, made another experiment. He took a snake and severed the head at a blow. While the trunk was writhing on the ground he touched it with a red-hot iron bar, and the snake wound itself round it and did not desist, although its flesh was burnt and skin charred. And so, in this case too, the spinal cord producing these movements is unreasoning.
But how to explain all the other apparently reasoning acts?
The structure of the nerve-centres can itself give an appearance of intelligence to results which are purely mechanical. Let us assume that the nerve-paths passing to the various muscles from one side or the other transmit more or less easily the stimuli given off from the spinal cord. A drop of vinegar having been put on the leg of a frog, as before mentioned, certain muscles will at once move—that is, those of which the nerves oppose the least resistance to the stimuli produced in the centre. But if the animal cannot remove the cause of the irritation, the latter accumulates in the spinal cord, so increasing in force that the nervous tension makes a way for itself along more resisting paths, thus giving rise to other less usual movements.