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. 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 anÆsthetics 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 gray 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, modifying 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 evidence of sensation is merely mechanical reflexion. One would think that Physiology and Pathology had been silent on the facts of analgesia without anÆsthesia, 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. 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. Instead 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 exciting 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 equivalent 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 in 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 an impression is indirectly the reaction of the whole organism, and that no organ detached from the organism has more significance than a word detached from a sentence, is of far-reaching importance, and peculiarly worthy of attention in considering the Reflex Theory, because almost all the evidence urged in support of that theory presupposes the legitimacy of concluding what takes place in the organism from what is observed in an organ detached from its normal connections. No experimental proof is necessary to show that many actions take place unconsciously; the fact is undisputed. But does unconsciously mean insentiently? It is certain that the unconscious actions take place in a sentient organism, and involve organic processes of the same order as the actions which are conscious. It is also certain that many sentient processes take place unconsciously. For thousands of years men used their eyes, and saw as their descendants see, yet were unconscious of the blue sky and green of the grass. Were their visual reactions not of the same order as our own? So far as the optic apparatus is concerned, there cannot be a doubt on the point; yet in them the sensorium having a somewhat different disposition—the neural elements being differently combined—their reactions correspondingly differed. They too had optical Sensibility, and visual sensations; but they did not feel precisely what we feel.

34. I have chosen these somewhat remote illustrations for the sake of their psychological interest; but I might have confined myself to more familiar examples. Thus the contents of the consciousness of a man born blind cannot be the same as the contents of one who has had visual experiences, which will enter into the complex of every conscious state, because the visual organs will have affected his sensorium; nevertheless in the organism of the blind man there are conditions so similar to those of other men, and his experiences will have been so similar, that in spite of the modifications due to the absence of visual experiences, his consciousness will in the main resemble theirs. But now let us in imagination pursue this kind of modification, let us take away hearing, taste, and smell, and we shall have proportionately simplified the contents of consciousness—the reactions of the sensorium—in thus simplifying the organism. There still will remain Touch, Temperature, Pain, and the Systemic Sensations. There will still remain an organism to react on impressions. So long as there is a living organism, however truncated, there is a sentient mechanism. When the brain has been removed, the removal causes both a disturbance of function and a loss of function; the mechanism has been seriously interfered with; yet all those parts of the mechanism which still co-operate manifest their physiological aptitudes. The animal can live without its brain, ergo it can feel without its brain. Observation proves this, for it discovers the brainless animal manifesting various sensibilities, and combining various movements. The vision of the brainless animal is greatly impaired, but it nevertheless persists. The intelligence is greatly impaired, the spontaneity is reduced to a minimum; but still both intelligence and spontaneity are manifested.

35. The physiologist has only two conclusions open to him. Either he holds Sensation to be a property of nerve-tissue—and in that case he must assign it to the spinal cord as to the brain; or else he holds Sensation to be a function of an organ—and in that case, although analytically he may decompose the organism into separate organs, assigning special sensations to the reactions of each, he must still admit that in reality these organs only yield sensations as component parts of the organism. The notion of a separate organ, such as the brain, being the exclusive seat of sensation is thus seen to be untenable.

In popular phrase, “it is not the eye which sees, but the mind behind the eye.” It is not the stimulus which is the object felt—it is the change in consciousness—the reaction of the sensorium. No one would propound the absurdity that the retinal cells see, or the auditory cells hear (although by a conventional ellipsis these cells are said to be “percipient” of colors and sounds), yet many writers have no hesitation in asserting that the cerebral cells are the seats of these and all other sensations. In a hundred treatises may be read the most precise description of the transformation of molecular changes in the retinal cells into molecular changes in the cerebral cells, where, it is said, “we know that the stimulations become sensations.” Now who knows this? How can it be known? Nay, who, on reflection, fails to see that this cannot be so? If a sensation of sight were not much more than a molecular change in the cerebrum stimulated by a molecular change in the optic tract, three conclusions would follow, each of which is demonstrably erroneous:—

I. The cerebrum in a decapitated animal would respond by a sensation of sight to a retinal stimulation.

II. The animal deprived of its cerebrum could not respond by a sensation of sight to a retinal stimulation.

III. The same retinal stimulation would always produce the same cerebral process and the same sensation; whereas the sensation depends on the condition of the sensorium at the time.

36. The difference between the Reflex Theory and that here upheld is important in its general relations, and yet turns on a point which may easily appear insignificant. The Reflex Theory asserts that when a sensory nerve is stimulated, the excitation of the centre may either subdivide into two waves, one of which passes directly to the brain and there awakens sensation, the other passes over to the motor-roots and causes muscular contractions; or, instead of thus subdividing, the wave may pass at once to the motor-nerves, and then there is movement without sensation. This is obviously a restatement in anatomical terms of the observed fact that some reflexes take place consciously and some unconsciously. But what evidence is there for this anatomical statement? We have seen that there is none. According to all we actually know, and reasonably infer, the continuity of tissue and the irradiation of excitation are such that the stimulus wave must always affect the whole system, so that brain and cord being structurally united, their reactions must co-operate with varying energy dependent on their statical conditions at the time.243 37. The physiological fact that the irradiation is restricted to certain paths, and therefore only certain portions of the whole system are excited to discharge—the fact that stimulation takes effect along the lines of least resistance—is that which gives the Reflex Theory its plausible aspect. But this fact of restriction is not dependent on an anatomical disposition of structure, it is, as we have already seen (Problem II. §166), dependent on a fluctuating physiological disposition—a temporary statical condition of the centres. And it enables us to understand why the reflex action which is at one moment a distinctly conscious or even a volitional action, is at another sub-conscious or unconscious. When an object is placed in the hand of an infant the fingers close over it by a simple reflex. This having also been observed in the case of an infant born without a brain,244 one might interpret it as normally taking place without brain co-operation, were there not good grounds for concluding that normally the brain must co-operate. Thus if the object be placed in the hand of a boy, or a man, the fingers will close, or not close—not according to an anatomical mechanism, but according to a physiological condition: if the attention preoccupy his sensorium elsewhere, his fingers will probably close, probably not; if his sensorium be directed towards the object, either by the urgency of the sensitive impression, or by some one’s pointing to the object, the fingers will close or not close, just as he chooses—perhaps the hand will be suddenly drawn away. The centre of innervation for the fingers is in the cord, and from this comes the final discharge of the sensitive stimulation; but the neural processes which preceded this discharge, and were consequent on the stimulation, were in each case somewhat different. In each case the impression on the skin was carried to the cord, and thence irradiated throughout the continuous neural axis, restricted to certain paths by the resistance it met with, but blending with waves of simultaneous excitations from other sources, the final discharge being the resultant of these component forces. We may suppose the brain to be the seat of consciousness, and yet not conclude that the brain was unaffected because the fingers closed unconsciously; any more than we conclude that the retina of the unoccupied eye is unaffected by light when with the other we are looking through a microscope, and only see objects with this eye—though directly we attend to the impressions on the other eye we see the objects which before were unseen. We know that the muscles of the back are all involved in walking, standing, etc., but we are seldom conscious of their co-operation till rheumatism or lumbago makes us painfully alive to it.

38. The two main positions of the Reflex Theory are, 1°, that reflex actions take place without brain co-operation,—as proved by observation of decapitated animals; 2°, that they take place without brain co-operation,—as proved by our being unconscious of them.

To these the answers are: 1°. The proof drawn from observation of decapitated animals is defective, because the conditions of the organism are then abnormal—there is a disturbance of the mechanism, and a loss of some of its components. The fact that a reflex occurs in the absence of the brain is no proof that reflexes when the brain is present occur without its participation. 2°. The absence of consciousness cannot be accepted as proof of the brain not being in action, because much brain-work is known to pass unconsciously, and there are cerebral reflexes which have the same characters as spinal reflexes.

39. A prick on the great toe traverses the whole length of the spinal axis with effects manifested in various organs—the muscles of the limb, the heart, the chest, the eyes, etc. The leg is withdrawn, the heart momently arrested, the eyes turned towards the source of irritation, the thoughts directed towards relief. These effects can be observed—there are others which lie beyond our observation, and can only be revealed by delicate experimental tests. But even the observable effects are very fluctuating, because they depend on fluctuating conditions. All we can say is, that so long as there is continuity of structure, there must be continuity of excitation; and the brain structurally connected with the centre of a sensory impression, must necessarily co-operate more or less in the reactions of that centre. In other words, the brain, although not the exclusive seat of sensation, plays a part in every particular sensation, so long as it forms a part of the stimulated organism.

40. This view being so widely opposed to the views current in physiological schools, I was gratified to find Dr. Crichton Browne led by his researches to a conclusion not unlike it in essential features. In his essay on the Functions of the Optic Thalami245 (well worthy of attention on other grounds) he says: “Allowing the spinal cord a power of independent action, it may still be that it generally acts reflexly through, or in association with, a superior centre. The sensorial ganglia can undoubtedly act alone in a reflex manner, but they almost invariably consult the cerebrum before dealing with the impressions which they receive; so it may be that the spinal cord, though capable of spontaneous reaction, may yet commonly refer to some higher seat of compound co-ordination before sending forth an answer to any message brought to it.” What is here stated as a possible and occasional process, I consider to be a necessary and universal process. Dr. Browne acutely remarks that if “what may be termed the encephalic loop were an integral part of every reflex act, then the influence of an intracranial lesion in checking reflex action would not be difficult to understand”—and we may add the notorious influence of the brain in arresting reflex actions, and modifying them by the will, which is only explicable on the supposition that the cerebral and spinal centres are functionally associated. Dr. Browne further remarks: “In experimenting upon myself I have sometimes thought that when the toe is pricked the sensation of pain actually precedes the movement of withdrawal; and in experimenting upon patients with sluggish nervous systems I have certainly noticed that after the pricking of the toe the little cry of pain has anticipated the muscular contractions of the leg. Now this cry of pain is a secondary reflex act through the sensorial centre; it is the result of a discharge from efferent nerves from the summit of what we have spoken of as the encephalic loop line; and we should certainly not expect that it would be developed earlier than the primary reflexion upon the motor apparatus, unless indeed what we have regarded as the primary reflexion really itself took place by way of the loop line.”

41. The difference between a voluntary and involuntary act is not, I conceive, that in the one case the brain co-operates and in the other is inactive, but that while in both the brain co-operates, the state of the sensorium known as mental prevision or ideal stimulation, is present in the one, and absent or less conspicuous in the other. So likewise the difference between a normal reflex action accompanied, and the same action unaccompanied by consciousness, is not that the brain co-operates in the one and is inactive in the other, but that the state of the sensorium is somewhat different in the two cases. Movements which originally were voluntary and difficult of execution—accompanied therefore by brain co-operation—become by frequent repetition automatic, easy of execution, and unconscious—they are then said to depend on the direct action of the established mechanism. Granted. But what are the components of this mechanism? Are they not just those centres and organs which at first effected the movements? In becoming easy and automatic, the movements do not change their mechanism—the moving organs and the motor conditions remain what they were; all that is changed is the degree of consciousness, i.e. the state of the sensorium which precedes and succeeds the movement. It is this which constitutes the difficulty of the question. Some readers may consider that all is conceded when unconsciousness is admitted. But this is not so. My present argument is the physiological one that the brain co-operates in reflex actions whenever the brain is structurally united with the reflex centres; the psychological question as to whether consciousness is also involved in this brain co-operation must be debated on other grounds; and we have already seen that consciousness operates in gradations of infinite delicacy.

Observe a man performing some automatic action, such as planing a deal board, or cutting out a pattern, which he has done so often that he is now able to do it “mechanically.” It is certain that his brain co-operates, and that he could not act thus with an injured brain; yet he is said to act unconsciously, his brain occupied elsewhere as he whistles, talks to bystanders, or thinks of his wife and children. Yet the brain is acting as an overseer of his work, attentive to every stroke of the plane, every snip of the scissors; and this becomes evident directly his attention is otherwise absorbed by an interesting question addressed to him, or an interesting object meeting his eye: then the work pauses, his hands are arrested, and the automatic action will only be resumed when his attention is released—when he has answered your question, or satisfied himself about the object.

42. This is a step towards understanding the co-operation of the brain even in those connate reflexes which were not originally voluntary acts, but were from the first organized tendencies, and are capable of being realized in the absence of the brain. I admit that it is difficult to find proof of brain co-operation here, though I think the anatomical and physiological evidence render it highly probable. But distinct proof to the contrary would not suffice for the Reflex Theory—would not prove that reflex actions were insentient—unless there had previously been proved that which seems to me contradicted by the clearest and most massive evidence, namely, that the brain is the sole seat of sentience. This contradictory evidence we will now furnish.