Problems of Life and Mind. Second series, George Henry Lewes [e book reading free TXT] 📗
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81. Hitherto we have been considering phenomena manifested in the absence of the cerebral hemispheres, because it is in these that the majority of writers place the sensorium. There are, indeed, many authoritative writers who regard the ganglionic masses at the base of the cerebrum, and even those of the medulla oblongata, as participating in this sensorial property, which they refuse to the lower ganglia in the spinal cord. I cannot follow their logic. The cerebrum is by its position as a centre of centres, and its detachment from all direct innervation of organs, so different from the rest of the neural axis, that we can understand how it should be assigned a special function; although being of the same tissue as the other ganglionic masses, it must have the same property. And what that special function is I shall hereafter endeavor to set forth. But that the upper region of the spinal axis should differ so profoundly from the lower region as to be the seat of psychical processes, while the lower region is simply the seat of mechanical processes, is what I cannot understand, so long as the anatomical structure and physiological properties of the two regions are seen to be identical. The various centres innervate various organs, and have consequently various functions. As each centre is removed, we observe a corresponding loss of function—the organism is truncated, but continues to manifest such functions as have still their mechanisms intact. Let us suppose the brain or upper regions of the cord detached from the lower regions by a section of the cord; the animal will still live, and perform almost all its functions in the normal way, but there will be little or no consensus between the lower and the upper regions. Granting Sensibility to both, we must still see that the sensation excited in one will not be felt in the other. And this is the ground on which physiologists deny that the lower regions have Sensibility. Without pausing here to examine this point, which will occupy us in the next chapter, I assume that the positive evidence of Sensibility suffices to discredit that argument; and in furtherance of that assumption will cite an example of sensation and volition manifested by the lower portion of the cord when separated from the brain and upper portion.
82. The function of Urination is one which notoriously belongs to the voluntary class, in so far as it is initiated or arrested by a voluntary impulse, and it is one which, according to the classic teaching, has its centre in the brain. The grounds on which this cerebral centre is assigned are very similar to those on which other functions are assigned to cerebral centres, namely, observation of the suppression of the function when the pathway between certain organs and the brain is interrupted. But the careful experiments of Goltz287 have demonstrated that the “centre” of Urination is not in the brain, but in the lower region of the cord. When the cord is completely divided, Urination is performed in the normal way—not passively, not irregularly, but with all the characters of the active regular function. And, what is also noticeable, this function is so intimately dependent on Sensibility that it will be arrested—like any other function—by a sensation excited from the periphery—to be resumed when the irritation ceases. Now this arrest from a stimulation of sensory nerves takes place when the brain is cut off from the spinal centre, just as when the brain is in connection with it.
The same is true of Defecation, and the still more complex functions of Generation and Parturition. I can only refer the reader to the very remarkable case of Goltz’s bitch with the spinal cord divided in the lumbar region, if evidence be wanted for the performance of complex functions so long as the spinal centres were intact. It is true that Goltz considers these functions to have been independent of sensation; but that is because he has not entirely emancipated himself from the traditional views; for my purpose it is enough that he admits the functions to be dependent on sensorial processes.
83. To sum up the evidence, we may say that observation discloses a surprising resemblance in the manifestations of the cord and brain. In both there are reflex processes, and processes of arrest; in both there are actions referable to conscious and unconscious processes; in both depression and exaltation are produced by the same drugs; in both there are manifestations interpretable, as those of Discrimination, Logic, Instinct, Volition, Acquisition, Memory; in both there is manifestation of Sensibility—how then can we deny Sensation to the one if we accord it to the other?
NEGATIVE INDUCTIONS.
84. I fancy some reader exclaiming: “All your reasoning, and all your marshalled facts, are swept away by the irresistible evidence of human patients with injured spinal cords, whose legs have manifested reflex actions, and who nevertheless declared they had no sensation whatever in them. We can never be sure of what passes in an animal; but man can tell us whether he feels an impression, or does not feel it; and since he tells us that he does not feel it, cannot, however he may try, we conclude that reflex action may take place without sensation.”
As this is the one solitary fact which is held to negative the mass of evidence, anatomical and physiological, in favor of the Sensibility of the spinal cord, it is necessary that we should candidly examine it. No reader will suppose that during the twenty years in which I have advocated the doctrine expounded in this volume, I have not been fully alive to the one fact which prevented the general acceptance of the doctrine. From the first it has seemed to me that the fact has been misinterpreted.
85. Certain injuries to the spinal cord destroy the connection of the parts below the injury with the parts above it; consequently no impression made on the limbs below the injured spot is transmitted to the brain, nor can any cerebral incitation reach those limbs. The patient has lost all consciousness of these limbs, and all control over them. Hunter’s patient on being asked if he felt any pain when the prick caused his leg to kick, answered, “No: but you see my leg does.” This answer has been regarded as a drollery; I think it expressed a physiological truth. For on the assumption that the whole of the cerebro-spinal axis had one uniform property, corresponding with its uniform structure, and various functions, corresponding with the variety of organs it innervates, a division of this axis would necessarily create two independent seats of Sensibility, and interrupt the consensus of their functions. In such a case it would be absurd to expect that the cerebral segment could be affected by, or co-operate with, what affected the spinal segment.
Now, when a man has a diseased spinal cord, the seat of injury causes, for the time at least, a division of the whole group of centres into two independent groups. For all purposes of sensation and volition it is the same as if he were cut in half; his nervous mechanism is cut in half. How then can any cerebral control be obeyed by his legs; how can any impression on his legs be felt by his cerebrum? As well might we expect the man whose arm has been amputated, to feel the incisions of the scalpel, when that limb is conveyed to the dissecting-table, as to feel by his brain impressions made upon parts wholly divorced from organic connection with the brain.
86. But, it may be objected, this is the very point urged. The man himself does not feel the impressions on his legs when his spine has been injured; he is as insensible to them as to the dissection of his amputated arm. Very true. He does not feel it. But if the amputated arm were to strike the anatomist who began its dissection, if its fingers were to grasp the scalpel, and push it away, or with the thumb to rub off the acid irritating one of the fingers, I do not see how we could refuse to admit that the arm felt although the man did not. And this is the case with the extremities of a man whose spine is injured. They manifest every indication of sensibility. In the frog and pigeon the legs manifest the unmistakable control which we ascribe to volition. It is true that the man himself, when interrogated, declares that he feels nothing; the cerebral segment has attached to it organs of speech and expressive features, by which its sensations can be communicated to others; whereas the spinal segment has no such means of communicating its sensations; but those which it has, it employs. You can ask the cerebral segment a question, which can be heard, understood, and answered; this is not the case with the spinal segment: yet if you test its sensibility, the result is unequivocal. You cannot ask an animal whether it feels, but you can test its sensibility, and that test suffices.
87. The question we have to decide, therefore, is not whether a patient, with an injured spine, can feel impressions on, or convey voluntary impulses to, limbs below the seat of injury—for as respects the nervous mechanism these limbs are separated from him, no less than if actual amputation had taken place—the question is, whether these separated limbs have any sensibility? And the answer seems to me unequivocally affirmative. I assert, therefore, that if there is ample evidence to show that the spinal centres have sensibility, when separated from the cerebral centres, such evidence can in no respect be weakened by the fact that a man with an injured spine is unconscious of impressions made below the seat of injury; since such a fact necessarily follows from the establishment of two centres: the parts above are then not sensitive to impressions on the parts below; nor are the parts below sensitive to impressions on the parts above; but each segment is sensitive to its own affections.
88. Every one knows that there are animals, low down in the scale, which may be cut in two, each half continuing to live, and each capable of reproducing its lost segments. Would any one, seeing these separated halves move and manifest ordinary signs of sensibility, venture to say that the one half was a living, the other an insentient, mechanism? And since the one half had eyes, mouth, tentacles, etc., while the other half had none of these, would the observer be surprised that the functions of the one differed from those of the other in these respects? Why, then, should he not conclude the same of the two halves of the human mechanism, when disease had divided them?
89. The man, you urge, does not feel the prick on his leg. This is true, because “the man” here designates the seeing, hearing, tasting, smelling, talking, thinking group of organs—to the exclusion of the limb or limbs which are no longer in sensitive connection with this group. When a leg is amputated “the man” remains—a truncated man, indeed, yet still one having all the distinguishing human characters. Yet obviously in strict language we can no longer say that the man is the same as he was. “Man” or “animal” means the complex whole; and each anatomically separable part forms one
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