Ability to feel depends on the maintenance of a certain temperature. This also is a general truth of which somo proof is furnished to every individual by his own experience — or, at any rate, to every individual inhabiting a climate where the winter's frost suffices greatly to chill the extremities. Evidence much stronger but indirect, is given him by those who have undergone surgical operations in parts deprived of feeling by freezing mixtures or by etherspray. Loss of local sensibility from local cold, ordinarily not very manifest unless the cold is great, becomes manifest when the cold is slight if the circumstances supply a delicate test. This is interestingly shown among compositors. The air of a printing-office has to be kept very warm, even at I the expense of unhealthy closeness; otherwise the fingers of the compositors cease to lay hold of, and manipulate, the types with the requisite nicety and speed.
Few persons have immediate experience of the fact that defect of blood in a part causes defective sensibility of that part; but all persons have immediate experience of the local exaltation of sensibility that accompanies local excess of blood. The inflamed neighbourhood of a wound, or even the surface of a pimple, yields to consciousness when touched, an amount of feeling far greater than is yielded by a part of the skin supplied with the ordinary amount of blood. Special organs of touch show us well the increased sensitiveness thus caused. When one of those sacs containing the bulbs of the small hairs scattered over the skin, is congested, the rubbing of the clothes against the hair growing from it, especially if it has been broken short, produces an unbearable smart. Among evidences yielded by the other senses, a familiar one is the intolerance of light that goes along with inflammation of the eyes. And there is an unfamiliar one particularly worth noting, because is exhibits the effect due to increased quantity of blood apart from increased temperature. The observation may be made when taking a hot bath. Let the water be above blood-heat — say 100° Ph. After remaining quiet for a time until equally heated all over, stand up and rub one portion of the body with a flesh -brush until it is red. Pause for a few moments, and Me down again in the water. It will then be perceived that to the reddened part the water seems much hotter than it does to any other part.* That degree of feeling is affected by quality of blood as well as by quantity,, is a truth not easily discerned within the * This fact yields proof, if there needs any, that the nerves which, appreciate temperature are not the nerves of touch. "Violent friction must produce a momentary incapacity of the nerves of touch; and this incapacity would be shown in a decreased, instead of an increased, appreciation 01 temperature, were they the agents concerned.
experiences of each individual, if attention is limited to those variations of feeling that accompany naturally -produced variations in quality of blood. For such variations cannot he identified with precision; and they arise so slowly that the concomitant mental states cannot be brought into close contiguity,, so as to bring out their contrasts clearly. But by making certain artificial additions to the blood, every one gets proof of the connection between its quality and the genesis of feeling. The effects of stimulants on consciousness are mostly traced in the intensification of those internally-initiated feelings with which we shall deal presently; but they may also sometimes be traced in the intensification of the externally - initiated feelings. In nervous subjects, ordinary impressions on the senses are often rendered abnormally acute by tonics. When under the influence of opium, music that was previously uneiijoyed may be greatly enjoyed; and it is a well-known result of hashish to give an excessive vividness to the sensations.
How, contrariwise, there are substances which, when added to the blood, render sentiency less vivid, is shown by other facts similarly reached. We have sedative medicines — medicines that diminish the amounts of painful consciousness caused by irritations at the periphery of the nervous system. And we have agents of the same class called anaesthetics, which, in a still greater degree, hinder the genesis of feelings by the actions that usually generate them. These effects so caused, help us to understand the stupor produced by the natural anaesthetics, carbonic acid and urea; and prove that some variations in degree of feeling are determined by variations in the activities of excreting organs.
§ 43. Now^that we have noted how ^fe^lings^and nervous changes are facilitated or hindered by the same conditions, we I may go on to collate them in detail. Let us begin by distin-f flushing those nervous changes which are accompanied "by feelings from those which are not. For, as we noted in; passing, several classes of them have objective aspects only | — d0 not present inner faces to consciousness; and others (have subjective aspects in early life but cease to have them. ;!in adult life.
r Chief among the nervous changes that have able subjectivg^aspectSj are those occurring in J^.."V ' ^° lorLo as "^ney are normal in their I amounts, the stimulations and discharges of which the ^sympathetic is the seat, go on without sensations; and even when abnormal, the resulting discomfort or pain is probably not due to them but to disturbance of those cerebro -spinal fibres whichaccompany the sympathetic through allitsbranchings. Similarly with the local ganglia and fibres of the heart. Ordinarily there is no consciousness of the heart's action; and even when the pulsations are violent, the modifications of consciousness do not arise from the state of the heart's nervous system,, but from disturbance of cerebro-spinal nerves caused by the bounds of the heart against adjacent structures. The like holds with the vaso -motor nerves. Under ordinary conditions these regulate the diameters of the arteries without our knowing anything about it; and though where, as in a blush, great dilatation of the vessels has been produced, we are made aware of their action, yet we are made aware of it indirectly, through the local change in the quantity of blood and the consequent effect on the nerves that appreciate temperature.
I The majority of stimulations and discharges^ occurring^ in.
I the spinal cord, have subjective accompaniments. These, I however, are not localized at those points in the spinal cord where the essential nervous changes take place; as is proved by the fact that when some lesion of the spinal cord which has not injured its lower part, has cut off communication with the brain, the reflex acts performed by this lower part are unconscious. Proceeding upon the inference before drawn (§21) tliat wlien a wave of disturbance brought by an afferent nerve to a spinal centre, liberates a quantity of molecular motion, a portion of it, not discharged along the efferent nerves, is propagated through a centripetal nerve to a higher centre, we may conclude that it is this portion which comes, in the higher centre, to have a subjective aspect as a sensation: being there joined with other sensations and feelings of other orders into a chain of states of consciousness, out of which no sensation is ever known to exist. For recognition of a sensation as such or such, necessitates the bringing of it into relation with the continuous series of sentient states, from some of which, simultaneously experienced, it is dissociated by perceived unlikeness, and with others of which, previously experienced, it is associated by perceived likeness; and the implied comparisons of sentient states are impossible unless the correlative nervous changes are put in connexion at one place. It does not follow, as it at first seems to do, that feelings are never located in the.inferior.Jiervous jcentres. On the contrary, it may well be that in lower types the homologues of these inferior centres are the seats ofjconsciousness. The true implication is that in any case the seat of consciousness is that nervous centre to which, mediately or immediately, the most heterogeneous impressions are brought; and it is not improbable that in the course of nervous evolution, centres that were once the highest are supplanted by others in which co-ordination is carried a stage further, and which thereupon become the places of feeling, while the centres before predominant become automatic.
Quite congruous with this conception is the above-named i fact, that ^certain nervous changes which...tave^ubjecti^e:f sides ^any in life cease 'to "lave thent later jnj.ife. Many* acts performed by the child slowly and consciously, the adult performs rapidly and unconsciously. Every step taken during the first efforts to wa]k has its accompanying 106 THE DATA Otf PSYCHOLOGY.
^distinct feelings; but eventually,, the successive steps are made while consciousness is wholly or almost wholly occupied with other feelings. Still better is the illustration furnished by speech. Each muscular adjustment of the vocal organs and each articulate sound made, have, in childhood, concomitant sentient states that are vivid, and, for the moment, all-absorbing. Gradually, however, these become less dominant in consciousness; until at maturity there is entire oblivion of the one, and sometimes partial oblivion of the other: witness the not unfrequent verbal mistakes unconsciously made in the heat of discussion. Now facts of this kind, countless in number and of many varieties, are explicable if we regard feelings as the subjective sides of such nervous changes only, as are brought to the general centre of nervous connections. When we remember that early in life each inferior ganglion, or cluster of cooperating interior ganglia, is imperfectly organized, and the connections among its fibres incomplete; we shall see that if there comes to it a disturbance, the gush of molecular moiion liberated, not having in the incompletely-connected cornmissnral and efferent fibres, adequate channels of escape, will part of it escape along a centripetal fibre to a higher centre, so awakening a feeling. And it will manifestly happen that the approach to automatic action, of the lower centre, will be an approach to a state in which the liberated molecular motion, having in the efferent fibres fully-opened channels of emission, will little or none of it be forced into centripetal fibres, and will so awaken little or no feeling. It is a corollary from this interpretation, that all gradations will exist between wholly unconscious nervous actions and wholly conscious ones; since there will be all gradations in the relative amounts of the disturbances which take their courses along centripetal fibres. It obviously follows, too, that in adult life a nervous action may or may not have an identifiable subjective aspect,, according as it is strong or weak; since, if there conies to a finished ganglion constructed as described, a feeble disturbance, the whole of the small quantity of molecular motion liberated may be drafted off by the efferent fibres; whereas, if the disturbance is great, the disengaged molecular motion, beiug more than can find its way along the efferent fibres, will some of it take a centripetal course and cause a subjective change.
§ 44. A kindred aspect of this correlation presents itself when we contemplate feeling as occupying time. A subjective state becomes recognizable as such, only when it has an appreciable duration: it must fill some space in the series of states,, otherwise it is not known as present. This general truth harmonizes with a general truth before pointed out respecting nervous action,, as well as with the above interpretation.
The observed fact that time is taken in the transit of a nerve-wave, is not to the point; for this transit has no concomitant subjective state. But the inferred fact that the change set up in a nerve-centre must take time, and a more considerable time (§ 85), is relevant; for what is I objectively a change in a superior. nerve- centre is subjectively! a feeling, and the duration of it under the one aspect measures the duration of it under the other. • That feeling persists after the_force arousing it ceases, is not proved by the lengthened sensation produced by a moderate blow on the skin, or by that which follows dipping the hand into hot-water, or by those which the palate and the nostrils experience from pungent substances momentarily applied; for though in such cases the external; action of the exciting agency is brief, the local changes it; sets up, lasting some time, continue for some time to disturb the local nerve-fibres. But good evidence is supplied by im^e^sian^_on^the_retina. To quote the words of Professor Huxley: — " A flash of lightning is, practically; instantaneous, but the sensation of light produced "by that 108 THE PATA OF PSYCHOLOGY.
flash endures for an appreciable period. It is found, In fact, that a luminous impression lasts for about one-eighth of a second; whence it follows,, that if any two luminous impressions are separated by a less interval, they are not distinguished from one another. For this reason a ' Catherine-wheel/ or a lighted stick turned round very rapidly by the hand, appears as a circle of fire; and the spokes of a coach-wheel at speed are not separately visible, but only appear as a sort of opacity, or film, within the tire of the wheel/' As above said, this general truth that feeling implies.time,, harmonizes with the interpretation given in the preceding section; and supplies a further elucidation of the relation between conscious and unconscious nervous action. For manifestly, in proportion as nervous co-ordinations become more automatic they become nic-re rapid; and for this reason also, cease to present such conspicuous subjective aspects. Returning to the inferior ganglion, or cluster of co-operating ganglia, above described, it will be obvious that a state in which the local organization is incomplete, and the various afferent and comniissural fibres not brought into definite relations with vesicles, and through them with efferent fibres, must be a state in which the molecular motion liberated by an incoming shock of change, will pass through the imperfectly differentiated structure with comparative slowness; and there will therefore be an appreciable time during which centripetal fibres may receive disturbance. But as fast as the local connections of fibres and cells become complete, the gush of molecular motion, following the completelyformed channels, will escape rapidly; and the period during which excitement of the centripetal fibres may take place will be abridged. The concomitant subjective state will therefore be rendered shorter by the same change that rondcrs it feebler.
§ 45. Tlie fact that each feeling lasts an appreciable timeT introduces us to the allied fact that each, feeling produces a greater or less incapacity for a similar feeling, which also lasts an appreciable time. This, too., is the subjective side of a, phenomenon before noticed under its objective side (§ 36). For as the duration of a feeling answers to the duration of the molecular disintegration in a disturbed nerve-centre; so the subsequent interval of diminished ability to feel, answers to the interval during which the disintegrated nerve-centre is re-integrating itself. Let us observe how among sensations of all kinds we may trace conformity to this law.
An illustration is supplied by the sense of touch. If the fingers be repeatedly swept rapidly over something covered bv numerous small prominences, as the papillated surface of an ordinary counterpane,, a peculiar feeling of numbness in them results: the objects touched the moment after seem smoother than usual; implying that the small irregularities on them produce less vivid impressions. That the sensation of muscular tension undergoes a variation similarly caused-, everyone knows. After carrying- a very '• heavy body in the hand for some time, a small body held;, in the same hand appears to have lost its weight; showing that the nerve-centre which is the seat of the sensation has been, for the moment, rendered obtuse. How the ' gustatory faculty is exhausted for a time by a strong taste, daily experience teaches. When sugar or honey has just •• been eaten, things that are but slightly sweetened seem to have no sweetness. While the palate is still hot with a curry, an un-flavoured dish seems insipid; and a glass of liqueur is fatal to the appreciation of a choice wine. Even more marked is that incapacity of the sense of smell caused in like manner. The intensity of tlie "pleasurable feeling given by a rose held to the nostrils, rapidly diminishes; and when the sniffs have been continued for some time, scarcely any scent can be perceived. A few minutes5 rest partially restores tlie impressibility; but a long interval must elapse before the odour •is enjoyed as keenly as at first. This quick exhaustion,, producing in such cases some disappointment,, lias its correlative advantage when, the smells are disagreeable. Very soon these become much less perceptible; and to those living in it a stench gives scarcely any annoyance. The feelings generated by sonorous vibrations rarely show us this variation in a marked degree; being, as they commonly are,, too short to leave much nervous prostration. A strong taste,, or odour, or sensation of muscular tension, is due to an action on the nerves that is maintained for a considerable time; but the actions to which are due those loud sounds required to cause temporary unixnpressibility, are mostly very brief. Illustrations are to be expected only in special cases; and in these we find them. The bang of a cannon is described as deafening by those who are close to the cannon when it is fired, because they are rendered for a time partially deaf to ordinary sounds. On men engaged in artillery-practice, the repeated explosions entail a dulness of hearing that lasts for hours; and this dulness of hearing becomes permanent in those who are permanently occupied in such practice. Numerous and very conclusive proofs are supplied by the feelings we receive from light. There are two classes of them: those showing us a variable sensibility^ to light in general, as contrasted with darkness; and those showing us a variable sensibility to each kind of light — each colour. Under the one head the reader may first be reminded of the experience that on going shine into a dimly-hghted place, it is i^ the "surrounding objects: only after a "time do they become faintly visible, and a considerable interval elapses before they are seen with clearness. Disabilities similarly caused are disclosed, when, instead of acting on the retinae as wholes, we act differently on their different parts. Hence what are called £STEO-PHY8IOLOGY. Ill negative images. If, after gazing for some moments at an object presenting strong contrasts of light and dark parts, the eyes are turned towards a shaded space, containing nothing conspicuous, there will be perceived a transient image of the object, in which the light and dark parts are reversed. The interpretation of this fact is that those portions of each retina on which strong light had fallen, together with the answering portions of the optic centres, having undergone the most change with corresponding production of the most feeling, are the next instant less capable of undergoing change and evolving feeling than the portions on which feeble light had fallen; and hence, when they are together exposed to the same feeble light, the unexhausted parts appreciate it more than the exhausted parts, and a negative image results. The cases of the second class are the well-known phenomena of subjective complementary colours. After looking intently at a surface of bright red, an adjacent surface of white seems to have a greenish tint. The explanation is obvious. Those nervous elements changed by the rays which produce in us the sensation of redness, having been partially incapacitated, the red rays contained in the white light cause less of their appropriate effect than usual; while the blue and yellow rays causing their usual effects, and therefore relatively-predominant effects, a sensation of greenness arises.
This decrease in the susceptibility to a feeling of any kind, which immediately follows a feeling of that kind, is not a constant decrease. It is a decrease that varies greatly in degree; and from its variation we may derive further instructive evidence. Other things equal, it is small or great ^ according to the.great or small constitutional vigour. One of these disabilities lasts for a scarcely appreciable time when the vital activities are high; and lasts for a time that becomes longer and longer as the vital activities flag. Abundant proof of this is famished by tie negative Images just described, la youth these are scarcely if at all to be observed: only when an extremely-vivid retinal impression lias been produced, as by looking at the Sun, is the negative image perceptible. But in middle life and afterwards, especially in debilitated persons, negative images of ordinary objects are very commonly perceived, and often have considerable durations.* Feeling being the subjective correlate of that which we know objectively as nervous action, these facts are obvious corollaries from facts set down in the last chapter. We there saw that the excitement of a nervecentre involves waste; and that restoration of the nervecentre to a state of equal susceptibility can be effected only by repair. Hence the return of fitness for what is objectively stimulation and subjectively feeling, will vary in quickness according to the rate of repair. When the blood is rich and rapidly circulated; the partial disability will be but momentary; and, unless the sensation has been intense, will be inappreciable. But along with failing nutrition of the tissues, the disability will become marked and its duration longer. In further illustration of this, I may name the fact that negative images are most. _ conspicuous on awaking in the morning, when the circulation is slow. The sense of hearing yields parallel evidence; though evidence of which the parallelism is not * This change comes on so gradually that very few remark it; and the usual supposition is that negative images are much the same at all ages and in all persons. I am able, however, to give personal testimony to the contrary. "When about twenty years of age, my attention was drawn by my father to a case in which the circumstances were favourable for perceiving the negative image, and in which he perceived it clearly. To me it was invisible; and I well remember Hs remark, that I should begia to see suck images as I became older. He was right. I now see them distinctly; and, moreover, I observe that they are most distinct at times of least Ti'{.-iir. It is worth while inquiring how far this change affects the ar.;.ref?ation of the chromatic harmonies. It seems inferable that the 2^^i>iiifis___of _coi::plrmeiitaiy colours become more immediately obvious. Persons on whom old age or debility brings deafness, frequently describe themselves as having no difficulty in hearing sounds, but as being unable to disentangle and identify words when they are indistinctly or rapidly uttered. Supposing that in such cases the nervous structures concerned suffer from faulty nutrition, we have an explanation of this peculiarity. For if each of the successive sounds entails waste of the auditory centres, and leaves them less sensitive to like sounds, it must follow that, when re-integration is slow, the like sounds immediately afterwards received will produce less than their due amounts of sensation. These defects of sensation will show themselves most in a comparative deadness to those delicate consonantal modifications by which words are mainly distinguished from one another — the utterances listened to will seeni a series of vowel-sounds joined by blurred consonants. Hence the reason why persons thus affected, ask those who address them to articulate slowly and clearly. The confusion of impressions produced by rapid speech on auditory centres thus debilitated, may be conceived by supposing debilitated optic centres to be similarly treated. If a person in whom the negative images are strong, has a series of objects passed before his eyes so fast that he can have only a momentary glance at each (to parallel the momentary opportunity which the ears have of identifying each successive articulation); then it will manifestly happen that the negative image of each object will interfere with, and confuse, the positive image of the next; and such a person will therefore not identify the successive objects so readily as one whose optic centres are repaired with normal speed. As confirming the be-Lief that this defect of hearing is so caused, I may add that it frequently co-exists with the defect of vision to which I have compared it j and also that the one, like the other, is most marked early in the day, and is diminished by whatever invigorates the circulation.
I ] ] 4 THE DATA OP PSYCHOLOGY.
§ 46. Another class of correlations demands a. passing notice. Up to tliis point, the feelings considered have been subjective aspects of those changes which objectively are nervous stimulations. We have now to consider certain other feelings which are the inner faces of what on their onter faces are nervous discharges. Having traced pretty fully the concomitance of sentient states and redpio -motor acts, it will suffice to trace briefly the concomitance of sentient states and dirigo -motor acts.
Certain inferior dingo-motor acts are unconscious; but omitting these,, the law is that with each muscular contraction there goes a sensation more or less definite. This is not a sensation indirectly produced through the nerves proceeding inwards from the skin, some of which are nearly always disturbed by each bodily motion; but it is a sensation directly produced, either by the discharge itself or by the state of the muscle or muscles excited. It is most clearly distinguished when, without touching anything and without moving, a leg or arm is held out at right angles to the body.
Vague as are feelings of this class in comparison with most feelings accompanying nervous stimulations, and much less numerous as are the varieties of quality among them, they are nevertheless so far definite and different that we can, to a certain extent, recognize..the separate feeling belonging to each separate contraction. We are aware without looking at it, and without touching anything with it, which finger has been bent by the discharge sent to its flexor muscles; and, by the particular combination of feelings accompanying the act, the placing of a limb in a given attitude is present to consciousness without aid from the eyes or hands. I say we can to a certain extent recognize the changes we thus set up; because the differences among the sensations of muscular tension soon lose much of their distinctness. It is a curious fact that when a limb has been held for some time in any position, especially if the position is one involving but little strain, the subjective state assoelated with, the nervous discharge to its muscles, becomes so indefinite that the attitude of the limb is unknown,, if there loes not happen to be a recollection of it.
Besides the connection between what we know objectively \ as a. particular motor act, and subjectively as a particular feeling of muscular tension, there is a connection between the; accompanying motor excitement propagated throughout the muscular system,, and a certain diffused feeling of which it is the seat. How along with each special nervous discharge;, there goes a general nervous discharge, we saw in the lastj chapter; and here we recur to the relation only to observe = that there is a parallel relation between the concomitant! states of consciousness. Thus the vivid sensation caused? by putting the foot into scalding water, does not lead only to the muscular contractions and muscular feelings which accompany the sudden withdrawal of the leg, but also to contractions of countless other muscles throughout the body, and a feeling called a shock or start.
Nor are these subjective states, special and general, that accompany special and general discharges to the muscles, the only subjective states that accompany discharges. As before pointed out, the vascular system and the alimentary system receive their shares of each discharge — very appre- -ciable when it is intense, and probably in no case wanting; and these, too, present inner aspects to consciousness. Sometimes, indeed, the feelings that go along with discharges into the vaso-motor and sympathetic nerves, are the predominant ones; as instance the thrill diffused through the body by certain acute creaking sounds said to ff set the teeth on edge;" or the nausea produced by particular kinds of disagreeable odours.
§ 47. Are these correlations between..iiervpus^ji the concomitant feelings quantitative, *? Is there such connection between a physical change in the nervous system and the psychical change accompanying it, that we may regard the one as an equivalent of tlie otter, in the same sense as we regard so mucli heat- as the equivalent of so much motion? The reader will perhaps expect an affirmative answer; but if an affirmative answer is to be given, it must be given in a greatly-qualified form.
On remembering that many nervous actions are always unconscious; on also remembering that various objective states of the nervous system, which have associated subjective states early in life, cease to have them later in life; and on remembering,, farther, that at the same period of life a change set up in an afferent nerve may cause an appreciable feeling, or may not cause it, according as the attention is free or occupied; we shall see that the connection between feelings and nervous changes is conditioned in a very complex way, and that if they are quantitatively related it can be only within the narrow limits implied by the complex conditions. If between a purely voluntary act and a purely automatic act there are gradations — if, at the one extreme, feeling is a conspicuous accompaniment, and, at the other extreme, ceases to be an accompaniment; then, clearly, in the intermediate phases the amount of feeling must bear a varying ratio to the amount of nervous change which the act implies. Again, if we assume that what is