23. The evidence is of two kinds: deductions from the general laws of nervous action, and inductions from particular manifestations. The former furnish a presumption, the latter a proof. The central process which initiates a reflex action may be excited by the external stimulation of a peripheral nerve, by the internal stimulation of a peripheral nerve, or by the irradiation from some other part of the central tissue. The last-named stimulations are the least intelligible, because they are so varied and complex, and so remote from observation; among them may be placed, 1°, the organized impulses of Instinct and Habit, with their fixed modes of manifestation; 2°, the organized impulses of Emotion, which are more variable in their manifestations, because more fluctuating in their conditions; 3°, the organized impulses of Intellect, the most variable of all. Whether we shrink on the contact of a cold substance or on hearing a sudden sound,—at the sight of a terrible object,—at the imaginary vision of the object,—or because we feign the terror which is thus expressed,—the reflex mechanism of shrinking is in each case the same, and the neural process discharged on the muscles is the same; but the state of Feeling which originated the change—or, in strictly physiological terms, the inciting neural process which preceded this reflex neural process—was in each case somewhat different, yet in each case was a mode of Sensibility.
491 24. The property of Sensibility belongs to the whole central tissue; and we have every reason to believe that unless it is excited no reflex takes place, whereas when it is exaggerated—as in epilepsy, or under strychnine—the reflex discharges are convulsive. When an?sthetics are given, consciousness first disappears, and then reflexion. When the sensorium is powerfully excited by other stimuli, the normal stimulus fails to excite either consciousness or reflexion. Hence our conclusion is that for consciousness, on the one hand, and normal reflexion, on the other, the proximate condition is a change in the sensorium; or—to phrase it more familiarly—Feeling is necessary for reflex action.
The difficulty in apprehending this lies in the ambiguity of the term Feeling. Many readers who would find no difficulty in admitting Sensibility as a necessary element in reflex action, will resist the idea of identifying Sensibility with Feeling. But this repugnance must be overcome if we are to understand the various modes of Sensibility which represent Feeling in animals, and its varieties in ourselves. We understand how the general Sensibility manifests itself in markedly different sensations—how that of the optic centre differs from that of the auditory centre, and both from a spinal centre. The tones of a violin are not the same as the tones of a violoncello, both differ from the tones of a key-bugle: yet they all come under the same general laws of tonality. So, as I often insist, the tissues in brain and cord being the same, their properties must be the same, their laws of excitation, irradiation, and combination the same, through all the varieties in their manifestations due to varieties of innervation. Hence it is that there are reflex cerebral processes no less than reflex spinal processes: the motor impulse from, the hemispheres on the corpora striata, or from posterior gray substance on anterior gray492 substance, is similar to that from the anterior gray substance on the motor nerves. The difference in reflexes arises from the terminal organs; as the difference in sensations arises from the surfaces stimulated. But not only are there reflex processes in the brain, of the same order as those in the cord, there are volitional processes in the cord of the same order as those in the brain. And in both the processes are sometimes conscious, sometimes unconscious. No evidence suggests that in the conscious action there is a sensorial process, and a purely physical process in the unconscious action—only a different relation of one sensorial process to others.
25. Let us contrast a cerebral and a spinal process, in respect to the three stages of stimulation, irradiation, and discharge. A luminous impression stimulates my retina, this excites my sensorium, in which second stage I am conscious of the luminous sensation; the final discharge is a perception, or a mental articulation of the name of the luminous object. But the irradiation may perhaps not have been such as to cause a conscious sensation, because the requisite neural elements were already grouped in some other way; in this case there is an unconscious discharge on some motor group, and instead of perceiving and naming the luminous object, I move my head, or my band, or my whole body, avoiding the object, or grasping at it. A third issue is possible: the irradiation, instead of exciting a definite perception, or a definite movement, may be merged in the stream of simultaneous excitations, and thus form the component of a group, and the discharge of this group will be a perception or a movement.
It is the same with a spinal process. An impression on the skin is irradiated in the cord, and the response is a movement, of which we are conscious, or unconscious. Here also a third issue is possible: the irradiation may be merged in a stream of simultaneous excitations, modifying493 them and modified by them, thus forming a component in some ulterior discharge.
26. The obstacle in the way of recognizing that cerebral processes and spinal processes are of the same order of sensorial phenomena, and have the same physiological significance when considered irrespective of the group of organs they call into activity, is similar to the obstacle which has prevented psychologists from recognizing the identity of the logical process in the combinations of Feeling and the combinations of Thought, i. e. the Logic of Feeling and the Logic of Signs. This obstacle is the fixing attention on the diversity of the effects when the same process operates with different elements. Because the spinal cord manifests the phenomena of sensation and volition, we are not to conclude that it also manifests ideation and imagination; any more than we are to conclude that a mollusc is capable of musical feelings because it is affected by sounds.
27. The careless confusion of general properties with special applications of those properties, and of functions with properties, has been a serious hindrance to the right understanding of Sensibility and its operations. Instead of recognizing that the nervous system has one general mode of reaction, which remains the same under every variety of combination with other systems, physiologists commonly lose sight of this general property, and fix on one mode of its manifestation as the sole characteristic of Sensibility. Sometimes the mode fixed on is Pain, at other times Attention. Thus, when an animal manifests no evidence of pain under stimulations which ordinarily excite severe pain, this is often interpreted as a proof that all sensation is absent; and if with this absence of pain there is—as there often is—clear evidence of the presence of some other mode of sensibility, the contradiction is evaded by the assumption that what here looks like evidence494 of sensation is merely mechanical reflexion. One would think that Physiology and Pathology had been silent on the facts of analgesia without an?sthesia, and of so much conscious sensation which is unaccompanied by pain.239 Who does not know that a patient will lose one kind of sensibility while retaining others—cease to feel pain, yet feel temperature, or be insensible to touch, yet exquisitely alive to pain?240 Inasmuch as Sensibility depends on the condition of the centres, an abnormal condition will obviously transform the reaction of the centres into one very unlike the normal reaction. For example, Antoine Cros had a patient who was quite unable to feel the sensation of cold on her left side—every cold object touching her skin on that side was felt as a very hot one; whereas a hot object produced “the sort of sensation which followed the application of an intermittent voltaic current.”241 Thus also the experiments of Rose242 and others have exhibited the effects of a dose of Santonine in causing all objects to be seen as yellow in one stage, and violet in another.
495 28. If, then, certain alterations in the organic conditions are accompanied by a suppression or perversion of some modes of Sensibility, without suppressing the rest, it is but rational to suppose that profound disturbances of the organic mechanism, such as must result from the removal of the brain, will also suppress or pervert several modes of Sensibility, and yet leave intact those modes which belong to the intact parts of the mechanism. Assuming that the spinal centres with the organs they innervate are capable of reacting under certain modes of sensation, these will not necessarily be suppressed by removal of the brain—all that will thereby be suppressed is their co-operation with the brain. I know it will be said that precisely this co-operation is necessary for sensation; and that the spinal reactions are simple reflexions in which sensation has no part. This, however, is the position I hope to turn. Meanwhile my assumption is that sensation necessarily plays a part in the reflex actions of the organism, and when that organism is truncated, its actions are proportionately limited, its sensations less complex. The spinal cord, separated from encephalic connections, cannot react in the special forms of Sensation known as color, scent, taste, sound, etc., because it does not innervate the organs of these special senses, nor co-operate with their centres. But it can, and does, react in other modes: it innervates skin and muscles; and the sensibilities, thus excited, it can also combine and co-ordinate. It has its Memory, and its Logic, just as the brain has: both no longer than they are integral parts of an active living organism: neither when the organism is inactive or dead. We do not expect the retina to respond in sounds, nor the ear to respond in colors: we expect each organ to have its special mode of reaction. What is common to both is Sensibility. What is common to brain and cord is Sensibility—and the laws of Grouping. Instead496 of marvelling at the disappearance of so many modes of Sensibility when the brain is removed, our surprise should be to find so many evidences of Sensibility remaining after so profound a mutilation of the mechanism.
29. The current hypothesis, which assumes that the brain is the sole organ of the mind, the sole seat of sensation, is a remnant of the ancient hypothesis respecting the Soul and its seat; and on the whole I think the ancient hypothesis is the more rational of the two. If the Soul inhabits the organism, using it as an instrument, playing on its organs as a musician plays on his instrument, we are not called upon to explain the mode of operation of this mysterious agent; but if the Soul be the subjective side of the Life, the spiritual aspect of the material organism, then since it is a synthesis of all the organic forces, the consensus of all the sentient phenomena, no one part can usurp the prerogatives of all, but all are requisite for each. And this indeed is what few physiologists would nowadays dispute. In spite of their localizing sensation in the cerebral cells, they would not maintain that the cerebral cells, nor even the whole brain, could produce sensation—if detached from the organism; the cheek of the guillotined victim may have blushed when struck, but who believes that the brain felt the insult, or the blow? Obviously, therefore, when we read that thought is “a property of the gray substance of the brain, as gravitation is of matter,” or that the brain is the exclusive organ of Sensation, the writers cannot consistently carry out their hypothesis unless they silently reintroduce other organs as co-operating agents; for a neural process in the cerebrum is in itself no more a sensation than it is a muscular contraction, or a glandular secretion: the muscles must co-operate for the contraction, the gland for the secretion, the neural process being simply the exciting497 cause. In like manner the Sensorium is necessary for the sensation, the neural process—in cerebrum, or elsewhere—being simply the exciting cause.
30. And what is the Sensorium? A long chapter would be required to state the various opinions which have been held respecting its seat, although amid all the disputes as to the organ, there has been unanimity as to the function, which is that of converting stimulations into sensations. I cannot pause here to examine the contending arguments, but must content myself with expounding the opinion I hold, namely, that the Sensorium is the whole of the sensitive organism, and not any one isolated portion of it. When light falls on the optic organ, or air pulses on the auditory organ, the reaction of each organ determines the specific character of the sensation, but no such sensation is possible unless there be a reaction of the organism; and the nature of the product will of course vary with the varying factors which co-operate—a simple organism, a truncated organism, an exhausted or otherwise occupied organism, will react differently from a complex, a normal, or an unoccupied organism. Detach the optic organ with its centre from the rest of the organism, and no normal sensation of Sight will result from its stimulation; and in a lesser degree this is equally true of a stimulation of the optic organ when the sensorium is exhausted, or powerfully affected by other stimuli. Because of the great importance of the cerebrum, and its predominance in the nervous system, it has been supposed to constitute the whole of the sensorium, in spite of the evidence of varied Sensibility after the cerebrum has been removed. I do not wish to understate the cerebral importance (see p. 166), yet I must say that the modern phrase cerebration, when employed as more than a shorthand expression of the complex processes which a cerebral process initiates, and when taken as the objective equivalent498 of Consciousness or of Thought, seems to me not more justifiable than to speak of Combustion as the equivalent of Railway Transport. The railway wagons will not move unless the fuel which supplies the boiler be ignited; the organism will not think unless the cerebrum excites this peculiar mode of Sensibility by its action on the organs. It is the man, and not the brain, that thinks: it is the organism as a whole, and not one organ, that feels and acts.
31. Consciousness, or Sensation, is a complex product not to be recognized in any one of its factors. Cerebral processes and spinal processes are the elements we analytically separate, as muscular contractions are the elements of limb-movements. The synthetic unity of these elements is a reflex; this we analytically decompose into a sensation and a movement; and then we speak of sensation as the reaction of the sensory organ, the movement as the reaction of the muscular organ. By a similar procedure we separate the stimulation of a sensory nerve from the reaction of the sensory organ, and that from the reaction of the sensorium; and in this way we may come to regard Cerebration as Thought. But those who employ this artifice should remember that the organism is not an assemblage of organs, made up of parts put together like a machine. The organs are differentiations of the organism, each evolved from those which preceded it, all sharing in a common activity, all inter-dependent.
32. That co-operation of the Personality which is conspicuous in conscious actions is also inductively to be inferred in sub-conscious and unconscious actions. We know that a man reacts on an impression according to his physical and mental state at the moment—that through his individuality he feels differently, and thinks differently from other men, and from himself at other epochs, and in other states. Because he resembles other men in499 many and essential points we conclude that he will resemble them in all; but observation proves this conclusion to be precipitate. Other men see a blue color in the sky, or feel awe at sight of the setting sun; but he has perhaps not learned to discriminate this sensation, is not conscious of the blue; nor has he learned to feel awe at the setting sun. Why—having normally constructed eyes—does he not see the blue of the sky? For the same reason that a dog, or an infant, fails to see it. The color has no interest for him (and all cognition is primarily emotion), nor has this want of personal interest been rectified from an impersonal source: he has never been taught to distinguish the color of the sky; and his eye wanders over it with the indifferent gaze with which a savage would regard a Greek codex.
33. The point here insisted on, namely, that every reaction on ............