Such are the phenomena which in the various species of animals follow the removal of the true brain. Many of the acts are seemingly so purposive, and certainly so complicated, as to suggest that they must be conscious. It has, however, been shown that the fact that an act is apparently purposive and complicated does not prove that it originates in consciousness, and certainly in the brainless animal the past, present and future have been blotted out. There is absolutely no conscious memory, else the needed food would be taken when offered and spontaneous movements would occur. It is hard to conceive of consciousness without memory, and it is certain that no purposive act can be directed by consciousness when memory does not exist in any degree or form. If all memory be lost, though consciousness be preserved, that consciousness would not have the knowledge which should enable an animal to perform a complicated purposive act; nor could it acquire knowledge by experience, because each movement would be forgotten as fast as produced. The phenomena exhibited by the brainless animals must therefore rest upon some other basis than consciousness. The first point to be observed in looking for this basis is that movements never occur so long as there is no external irritation. The frog, the pigeon, the rabbit, all maintain the same absolute repose unless the impulse comes from without. The fish is a seeming, but not a real, exception to this rule. The frog, the pigeon, the rabbit, all are quiet on the land, because their surface is not irritated: the fish in the water rushes forward, because the play of the liquid is all the time irritating the exterior of the body. Throw the frog into the water, and it is seized with the madness of the fish; toss the pigeon in the air, and it dashes forward; set the rabbit once in motion, and its course also is a headlong fury. Placed under parallel conditions, these various animals exhibit parallel phenomena, and remain quiet unless disturbed by surface-irritations. The facts show that for action in the animal whose upper brain has been removed some external irritation must generate the impulse, which travels upward to a nerve-centre, and then brings into activity certain masses of nervous tissue (ganglia), which, thus aroused, send impulses out to the various muscles without the intervention of consciousness. Movements generated in this way are reflex or automatic. In brainless[2] animals the reflex actions are not different in their essence, but only in their degree, from those performed in the frog with a cut spine; or, in other words, the acts originating in the lower brain are reflex and similar to those arising in the spinal cord, only more complicated and more apparently purposive.
The complexity of the reflex movements which are produced through the lower brain indicates a corresponding complexity in the apparatus concerned. In accordance with this, we find that whilst only one kind of nerves capable of carrying impulses from the surface to the nerve-centres enters the spinal cord, to the lower brain pass not less than five distinct varieties of afferent nerves, which carry impulses of as many different characters to the centres. Contact is necessary to arouse reflex movements through the spinal cord. The effect of a pistol report upon a brainless animal demonstrates, however, that its nerve of hearing is capable of carrying to the middle brain an impulse which stirs that centre to action. The brainless pigeon follows with its head the lighted candle: its nerve of sight is therefore capable of taking part in the creation of a reflex movement. The same bird will eat largely when appropriate food is placed in its mouth—an indication that the nerve of taste is also active. In a word, to the middle brain the nerves of sight, of hearing, of tasting, of smelling, as well as those of common sensibility, bear impulses which find their appropriate nerve-centres and give origin to complicated reflex movements. Partly in the number and variety of the afferent nerves, and partly in the number and variety of the nerve-centres crowded into the lower brain, lie the causes of the great intricacy of the automatic movements which originate in this region.
Of all the acts performed by the brainless frog, fish, bird or mammal, the most difficult to understand are those connected with standing, jumping, swimming, walking, flying, running, etc.; or, in other words, with equilibration, or the function of maintaining the equilibrium. Why does the brainless frog, the automaton, shift his position as the board upon which he sits is slowly tilted? There are apparently no new contacts of the skin: the motion is so quiet, so gentle, that it would seem as if there was nothing to produce irritation of the surface of the body so as to cause reflex acts. If it be true, as is asserted by some observers, that taking off the skin of the legs of the frog (a procedure which causes no pain, as the frog has no consciousness) prevents his shifting himself to maintain his equilibrium when his resting-place is moved, it is plain that the surface-irritations which cause the reflex alterations of position in the brainless frog originate in the skin of the legs and through the sense of touch. There are, however, certain facts which indicate that the impulses under discussion are not of so simple a character.
Before inquiring into these facts it should be observed that there is no movement which the uninjured frog ever performs to restore his equilibrium that the brained frog does not also make with equal promptness. Lay it on its back, on its head, twist its legs into unnatural positions, fix it as you may, so soon as released this unconscious automaton restores itself to its sitting posture. This being the case, it is plain that all the machinery of equilibration must be present in the mutilated frog, and must therefore be situated in the lower brain and its dependencies; and, further, that when the uninjured frog consciously attempts to maintain the erect position or to alter the gait, it simply calls into action the machinery provided for it in the lower regions of the nervous system. What is true of the frog is also true of the man; and the question naturally arises, What is the character of this machinery which the conscious will employs? This apparatus consists of two parts: first, certain exterior parts which are affected by disturbances of the equilibrium, and which when thus excited send up impulses to the lower brain; beyond, certain nerve-centres which when aroused by impulses derived from the external parts send back in a reflex manner impulses to the various muscles, which by their contraction produce motion or rectify the mistakes of position. Touch has much to do with equilibration: sight also has much to do with it. There is a disease of the spinal cord known as locomotor ataxia which destroys the sense of touch in the legs. A person suffering from this disorder is said to be ataxic. When a completely ataxic man puts his feet upon the pavement he feels nothing. Under these circumstances the man is unable to walk with his eyes shut. Even if the ataxia be not complete and some sense of feeling remain, the gait becomes so uncertain that progression is impossible. The pavement feels nearer or farther off than it is, and the result reminds one of his experiences in going up stairs in the dark and stepping out at the top in the belief that another step exists. Long before sensation is completely paralyzed the power of walking in the dark is entirely lost by the ataxic; for, indeed, the man, who has still as much muscular power as ever in his legs, may be unable to walk under any circumstances or even to stand unaided by a cane. The movements are vigorous, but uncontrollable: the legs fly about in all directions, refusing to obey at all the most strenuous efforts of the will.
The loss of the sense of touch in the skin is not, however, the sole or even chief reason that the ataxic man cannot walk. I once saw a patient who could march very well by night or by day, although the skin of his legs was so dead that a live coal would scarcely awaken it. The sense that is wanting in locomotor ataxia is that form of general sensibility which is known as the muscular sense; that is, that sense or feeling which tells the lower brain exactly how much a muscle is contracted, and when to urge it more, when to let it relax. This is evidently a guiding sense, of whose action we are barely conscious, but of whose existence there is no doubt. We do not feel a muscle contract ordinarily, but we do so when attention is directed to a muscle at work. Thus we judge of the weight of a body by the amount of force which our muscles must put forth to lift it. Any one can satisfy himself by a very simple experiment that the judgment of weight is not founded upon pressure on the skin. Lay the hand upon the table, place the heavy body upon it and try to judge of the weight. Again, whenever we endeavor to estimate accurately how heavy a body is, we raise it again and again into the air, evidently that we may feel the muscles contract again and again, and by repeated efforts judge how much of force they put forth.
The phenomena of ataxia are of great importance as corroborating the experimental proofs spoken of a few pages back, which show that walking is automatic and not simply performed by a conscious power of the will. Thus the ataxic may be able to walk with his eyes open, when he cannot even balance himself erect with his eyes shut. If the conscious will really did by a direct effort produce walking, it should be able to control the movements by itself, and the ataxic man should be able to walk although impulses from the exterior of the body no longer reached his lower brain. The man who turns a cog-wheel himself is independent of external power, but the man who directs a clockwork moved by a spring can only push back the stop and release the spring: if the spring be broken he is powerless. The impulses from the exterior are the springs of locomotion, and all the will can do is to withdraw the checks and call the machinery of walking into action. When the external impulses are no longer transmitted to the lower brain walking becomes impossible.
As already shown, general sensibility, including in the term the sense of touch and the muscular sense, is of prime importance in equilibration, but it is unquestionable that the nerves of the other senses carry to the nerve-centre impulses from the external parts of the body which are necessary to the highest development of the function. The partially ataxic man can walk with his eyes open, although he does not feel the floor, because sight replaces touch. The blind man, certainly, cannot balance himself so well as he whose eyes are perfect. We all know that the sight of a yawning abyss or the gazing upon whirling objects is prone to produce giddiness.
Some experiments made by the English physiologist Crum Browne show that there must be guiding impulses which are connected with equilibration besides those already discussed. The observer mentioned found that if a blindfolded man lies on a table with a movable top placed upon a central pivot, he can judge in regard to the movements lateral or vertical, even if they be made so carefully and slowly that the man is perfectly quiescent. The subject under experiment is almost always able to decide correctly not only the direction of the motion, but also the angle through which the motion has extended. It is possible that the guiding impulses under these circumstances originate in all parts of the body. Thus, when we lie with the head downward we are at once sensible of a feeling of fulness or pressure due to the gravitation of the blood and other liquids of the body toward the head. Position undoubtedly affects the gravitation of liquids in all parts of the body: the man whose forces are reduced by a low fever gets a congestion of the back of the lungs if he lies too long upon his back. It may be that this flow of fluids toward any unusually dependent part of the body makes an impression upon the nerves of touch, which pass through all parts of the organism, and that in this way peripheral impulses are generated which reach the lower brain.
On the other hand, the extreme delicacy of perception of movement which some persons evince when laid upon the table-top would seem to require a more delicate apparatus than that just spoken of; and there are many facts which point to a peculiar structure in the inner ear as having connection with equilibration. If in the frog the disk back of the eye be wounded deep enough to affect the nerve of hearing, the creature falls upon one side, entirely deprived of its power of balancing itself. Perfectly similar phenomena are seen not only in the mammals operated upon by the physiologist, but also in human beings, in whom wounds of the nerve of hearing, as well as ruptures of blood-vessels in the inner ear, produce a peculiar vertigo, with staggering and loss of power which have been mistaken for apoplexy. Some years since there was under my professional care a man who had been shot in the face, the bullet passing backward toward the inner ear. In this case there was complete loss of hearing on the injured side, and a peculiar giddiness, with staggering gait similar to that which follows hæmorrhage into the inner ear. The bullet had certainly penetrated into the aural region, and the vertigo was evidently like the deafness due to an injury of the inner ear. In the inner ear of all animals are the so-called semicircular canals, which are provided with membranous walls, and are filled with liquid. At the end of each of these canals is an enlargement known as an ampulla, upon which is a delicate expansion of nerve-tissue derived from the nerve of hearing. These semicircular canals are so placed that every motion of the head must produce disturbance of the liquid contents of at least one of them, and consequently alterations of pressure on the nervous tissue in the ampulla. The structure and peculiar arrangement of these canals and their contents suggest very naturally that they have some other function than that of aiding in hearing, and that they are in some way connected with equilibration—that they are, as it were, the spirit-levels of the body, and that by the shifting of their contents impulses are constantly sent up to the lower brain to direct it in the maintenance of position. This suggestion is confirmed by the results of experiment: in the pigeon and in some mammals the canals can be readily reached and divided. Such injuries to them are followed by great disturbance of the motor function of the animal, the nature of the disturbance being chiefly dependent on the seat and character of the injury. Repeated somersaults backward or forward, bizarre contortions, spinning around worthy of a whirling dervish, loss of the power of balancing on a moving perch or board, staggering gait,—these and other similar phenomena mark the disturbance of equilibration produced by wounds of the semicircular canals.
The balancing of the body which occurs even in standing, much more that of walking, running or flying, is the result of a very complicated series of movements, numerous muscles antagonizing one another by regulated contraction, so that just the right position may be secured. To preserve the equilibrium innumerable unfelt impulses are continually passing from the eyes, from the semicircular canals, from the various muscles employed, up to the nerve-centres in the lower brain, where they are, as it were, assorted and reflected back as co-ordinated or arranged impulses to all parts of the muscular system, and produce just such contractions as are required for the purposes of equilibration and locomotion. When a child is learning to walk it is simply educating this intricate machinery and developing its latent powers. Very much as the will of man aids a setter in developing the natural instinct to hunt, so does the child's will direct, check and in every way assist the complicated and delicate machinery which presides over locomotion. Perhaps a better comparison is to be found in the drill-sergeant training and educating his squad of men, who at first are utterly unable to obey his will, but who by his reiterated efforts are finally so trained that they move as one piece in strict obedience to his word or go through complicated manœuvres without command. No wonder the child requires so many days of effort to get all its delicate machinery of walking, running, etc. so trained that it works smoothly and without conscious effort of the will. But as the training becomes more complete, the lower brain becomes more and more independent of the conscious will which resides in the upper brain or cerebrum, until at last the automatic action is so perfect that walking without consciousness is possible. Very many of my readers have no doubt in their younger days, when hard pressed with a lesson, walked to school studying as they went, their attention riveted on the book, their feet carrying them along the well-known pathway. Under such circumstances consciousness does not direct progression. Walking in the sleep is only one step beyond this. In the days of Antietam a friend of the writer's, worn out with the forced marching, whilst on guard as a sentinel, erect and soldier-like in posture, slept until the dark lantern of the relief officer appalled him with its sudden flash. Once after a long tramp I myself, laden with a heavy pack, nearing home, trudged in the unconsciousness of sleep along the oft-trodden road. In the cavalry raids around Richmond during our late war it was not very unusual for men and beasts to become so exhausted that both would go to sleep on the homeward night-march when they were straining all their powers to escape. The whole regiment asleep, horses staggering along in loose order, men swaying to and fro in their saddles, when there was a sharp turn in the road it was necessary to post sentinels to waken the passing ranks, which otherwise in the unconsciousness of sleep would have continued right on into bush or brake. Indeed, in one instance that came to my notice a horse with an officer on his back did in this way walk over a precipice some twenty feet high.