The Physical Basis of Mind / Being the Second Series of Problems of Life and Mind.

by George Henry Lewes

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 constituent of that whole. The medulla oblongata and spinal cord innervate certain parts; the mesencephalon innervates others; the cerebrum rises above the whole. If after removing one limb, then another, we continued truncating the organism till we left only the head, should we call that the man? Clearly not. Should we even suppose that the intact brain—the supposed seat of sensation and volition—still felt, and willed? Clearly not. There is absolutely no evidence, however faint, of the isolated head manifesting any sensational and volitional phenomena; whereas there is ample evidence of the truncated spinal cord manifesting some of these phenomena. And this is intelligible when we understand that the nerve-centres stimulate into action the organs they innervate, but do not by themselves play any other part.

90. “The man” then does not feel the prick on his leg, but his leg feels it. The man has no consciousness of what takes place outside the sphere of his sensitive mechanism; and the leg is now outside that sphere. Consciousness—as distinguished from Sentience in general—we have seen to be a resultant of the composition of forces co-operating at the moment; the Sensibility of the spinal cord in the regions below the injury cannot now enter into that composition. It is detached from the upper organs. But inasmuch as the organs it innervates are still living and active, the functions of this detached portion are still displayed. We have seen the dog with divided cord capable of Urination, Defecation, Generation, etc.; its hinder legs, though not moving in a consensus with the forelegs, yet moved independently; and all the normal reflexes of the parts followed on stimulations. To say that “the dog” showed no signs of Sensibility when its hinder limbs were irritated, is identifying “the dog” with the anterior half of the organism which was not in connection with the posterior half. It is equally true that the posterior half showed no signs of Sensibility when the anterior was irritated. The two halves were united by the circulation, nutrition, etc., but disunited as to sensation and volition.

91. Do I then suppose the separated half of an animal to feel pain and pleasure, hope and terror? The reader who has attentively followed the exposition will be at no loss to answer. Pain, pleasure, hope, and terror, are special modes of Sensibility, dependent on particular neural combinations. The organs comprised in the anterior half of the animal furnish the main conditions for these special modes, whereas the organs comprised in the posterior half furnish few or none of those—they contain none of the special Senses, and they are without the chief combining centre, the brain. But since we know that a large amount of normal Sensation is wholly without the special characters of pain, pleasure, hope, or terror, we need not hesitate to assign Sensation to the spinal cord because these characters are absent.

92. All I contend for is that the spinal centres have Sensibility of the same order as the cerebral centres; and that in the normal organism this Sensibility enters as a factor into the general Consciousness—no one portion of the nervous system being really independent of all the others, all co-operating in every result. Over and over again I have had to insist that the property of Sensibility is only the general condition of Sensation; and that each particular sensation receives its character from the organs innervated, plus the reaction of the whole organism. Obviously, therefore, the peculiar character of a sensation, or “state of consciousness,” must vary with the variations in either of these factors. To say that every segment of the spinal cord has Sensibility, is not saying that an excitation of that segment will produce a particular sensation of definite character; because for this definite character there is needed the co-operation of all those parts of the mechanism which enter into the complex product.

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93. And here attention must be called to a double fallacy pervading the arguments on the other side. It is always assumed that the reactions of an organ, or part of the organism, when separated from the rest, are typical of their reactions when forming constituents of the normal organism. Nothing of the kind. The movement of a muscle or a limb separated from the body may resemble that movement when normally effected—but only as the movements of a mechanical bird resemble those of a living bird: the modes of production are different. So that were we to grant the postulate of the brain being the exclusive seat of sensation, we should still deny that an action which was effected after removal of the brain was typical of the action effected when the brain was present. The leg of Hunter’s patient jerked when the skin was irritated; but this action could not be altogether the same as the similar action in a leg united with the rest of the sensitive mechanism. Nor is this all. The leg may have been insensible, the spinal segment which innervated it may have been wholly without Sensibility, and still we should have to question the logic which extended such an inference to the very different and far more complex actions of decapitated animals. On this ground:—The leg is, by the hypothesis, insensible because cut off from all connection with the sensitive mechanism. But this is not the case with the decapitated animal: there still remain the essential parts of a sensitive mechanism—all the chief organs are still in activity, still manifesting their functions. Decapitation has produced a great disturbance in the mechanism, and has removed an important centre; but nevertheless every impression excites a connected group of centres, and this group responds.

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