What then is lost? We have only to remember that the cerebrum is continuous with the thalami and corpora striata, and, through its crura, with the medulla oblongata and medulla spinalis, to foresee that its removal must more or less affect the whole neural axis, and consequently disturb the actions of the whole organism; this disturbance will often have the appearances which would be due to the removal of a central apparatus, so that we shall be apt to attribute the cessation of a function to the loss of its organ, when in fact the cessation is due simply to an arrest of the organ by irritation. Thus the cessation of consciousness, or of any particular movements, when the cerebrum is removed, is no decisive proof that the cerebrum is the organ of consciousness, or of the movement in question. This point will be duly considered hereafter. What we have now to consider is the facts observed after removal of the cerebrum.
First, we observe a loss of that power of combining present states with past states, present feelings with feelings formerly excited in conjunction with them, the power which enables the animal to adjust its actions to certain sensations now unfelt but which will be felt in consequence of the adjustment. Secondly, we observe a loss of Spontaneity: the bird, naturally mobile and alert, now sits moveless for hours in a sort of stupor, occasionally preening its feathers, but rarely quitting its resting-place. All the most conspicuous phenomena which we assign to Intelligence and Will seem absent. The sensations are altered and diminished. Many Instincts have disappeared, but some remain. The sexual feeling is preserved, although the bird has lost all power of directing its actions so as to gratify the desire. But these effects are only observed when the whole of both hemispheres have been removed. If a small portion remain the bird retains most of its faculties, though with less energy. In frogs and fishes there is little discernible effect observed when a large portion of the cerebrum is removed.
31. Now take away from this mutilated bird its cerebellum: all the functions continue as before except that some combined movements can no longer be effected; flight is impossible; walking is a mere stagger. Remove only the lateral lobes, and though flight is still possible great incoherence of the wings is observed, whereas walking is not much affected. If only the cerebellum be removed, the cerebrum being intact, the phenomena are very different. All the perceptions and almost all the emotions, all the spontaneity and vivacity are retained; but the sexual instinct, which was manifested when the cerebrum was removed, is now quite gone. What we call Intelligence seems unaffected. The bird hears, and understands the meaning of the sounds, sees and perceives, sees and fears, sees and adjusts its movements with a mental vision of unseen consequences.[92]
32. Are we from these facts to conclude that the cerebrum is the “organ of the mind”; that it is “the seat” of sensation, thought, emotion, volition; and that the cerebellum is the “seat” of the sexual instinct, and muscular co-ordination? Such conclusions have found acceptance, even from physiologists who would have been startled had any one ventured to affirm that the medulla oblongata was the “organ” of Respiration, because Respiration ceases when this centre is destroyed. I shall have to combat this notion at various stages of my exposition. Here let me simply say that it is irreconcilable with any clear conception of organ and function; and is plainly irreconcilable with any survey of psychical phenomena in animals in whom the cerebrum does not exist, and in animals from whom it has been removed.
What the facts indisputably prove is that the cerebrum has an important part in the mechanism by which the most complex psychical combinations are effected, and that the cerebellum has an important part in the mechanism by which the most complex muscular combinations are effected. The supreme importance of the cerebrum may be inferred from its dominating all the other centres, and from its preponderance in size. In man it stands to all the other cranial centres together in the relation of 11 to 3. It is about five times as heavy as the spinal cord—that is to say from 1,100 to 1,400 grammes, compared with 27 to 30 grammes. The quantity of blood circulating through it is immense. Haller estimated the cranial circulation as one fifth of the whole circulation. If, therefore, the Nervous Centres are agents in the production of Sensation and Intelligence, by far the largest share must be allotted to the cranial centres, and of these the largest to the Cerebrum.
33. It is, however, one thing to recognize the Cerebrum as having an important part in the production of psychical phenomena, another thing to localize all the phenomena in it as their organ and seat—a localization which soon becomes even more absurd, when of all the cerebral structure the multipolar cells alone are admitted as the active agents!
As was said just now, we recognize in the Medulla Oblongata the nervous centre of Respiration, but we do not suppose that Respiration has its seat there, nor that this centre is absolutely indispensable for the essential part of the process. We respire by our skin, as well as by our lungs; many animals respire who have nothing like a medulla oblongata; as many animals feel, and manifest will, who have nothing like a cerebrum. The destruction of centres is of course a disturbance of the mechanisms which they regulate. But even the observed results of a destruction require very close examination, and are liable to erroneous interpretations. The disappearance of a function following the destruction, or disease of a particular part, is not to be accepted as a proof that this part is the organ of the lost function; because precisely the same phenomena may often be observed following the destruction of a totally different part.[93] But one result may always be relied on, and that is the persistence of a function after removal of a particular part. Thus there is a certain spot of the cerebral convolutions from which movements of the limbs are excited when the electrodes are applied to it; removal of the substance is immediately followed by paralysis of the limbs. Are we to conclude that this spot is the organ of the function? It is true that the function is called into action by a stimulus applied to this spot: true that the function suddenly vanishes when the substance of this spot is destroyed. Nevertheless, what seems a loss of function is only a disturbance. In two or three days the paralysis begins to disappear, and at the end of a week the limbs are moved nearly in the normal manner. And the same is true when the spot in question is destroyed on both sides. The recovery of the function shows that the absent part was not its organ. There is a paradoxical experiment recorded by M. Paul Bert which may be cited here. He removed the right cerebral hemisphere from a chameleon, and found that the limbs on the left side were paralyzed; but on his then removing the left cerebral hemisphere the limbs of the left side recovered their activity. A similar result was obtained by Lussana and Lemoigne by extirpation of the thalami. When we find combined movements persisting after the cerebellum has been destroyed, we may be sure that the cerebellum is not the organ by which such combinations take place; and when we find sensation and volition manifested after the cerebrum has been removed, we may be sure that the cerebrum is not the organ for these sensations and volitions.
34. And this we do find. Physiologists, indeed, for the most part, deny it; or rather, while they admit the observed facts, they refuse to admit the only consistent interpretation, biassed as they are by the traditional conception of the brain. After having for many years persistently denied Sensibility to any centre except the cerebrum, they are now generally agreed in including the medulla oblongata within the privileged region; but they still exclude the medulla spinalis.
35. If all the cranial centres as far as the medulla oblongata are removed from young rabbits, dogs, or cats, there are unmistakable evidences of Sensibility in their cries when their tails are pinched, their moving jaws (as in mastication) when bitters are placed in their mouths, and their raised paws rubbing their noses, when irritating vapors are applied. It is said indeed that the cries are no signs of pain; and this is probable; but they are assuredly signs of Sensibility.
35. The frog thus mutilated has lost indeed all its special senses, except Touch, but it still breathes, struggles when grasped, thrusts aside the pincers which irritate it, or wipes away acid dropped on its skin. If the eye be lightly touched, the eyelid closes; if the touch be repeated three or four times, the foreleg is raised to push the irritant away; if still repeated, the head is turned aside; but however prolonged the irritation, the frog neither hops, nor crawls away, as he does when the cerebellum remains. Place the brainless frog on his back, and if the medulla oblongata remains he will at once regain the normal position; but if that part is absent he will lie helpless on his back. The power of preserving equilibrium in difficult positions—which of course implies a nice co-ordination of muscles—resides in the so-called optic lobes of the frog (what in mammals are called the corpora quadrigemina).