them from their insides. To speak with exactness, indeed, it cannot be said that we have so to contemplate these changes; for this expression implies that these changes can be simultaneously seen by more than one, which is not true. Rigorously limiting the proposition to that which is alone possible, it amounts to this: — I have to describe the laws of relation between the states of feeling occurring in ray own consciousness, and the physical affections of that nervous system which _I_ conclude ^possess; and the reader "has to observe whether in himself there exist parallel rela- tions between such known states of consciousness and such supposed nervous affections.
This will perhaps be thought a needlessly roundabout, if not a sceptical, statement; but it is in fact not roundabout enough. It does not bring sufficiently into view the re- J:STHO-PHYSIOLOGY.
motoly -inferential character of the belief tliat feeling and nervous action are correlated. Before proceeding on this belief, let us observe how indirect is the path which leads to it. — 1. Each individual is absolutely incapable of knowing any feelings but his own. That there exist other sensations and emotions,, is a conclusion implying, in the first place, the reasonings through which he identifies certain objects as bodies of like nature with his own body; and implying, in the second place, the further reasonings which convince him that along with the external actions of these bodies, there go internal states of consciousness like those accom- panying such external actions of his own body. 2. This conclusion that there exist beings like himself, and that under like conditions they experience like feelings, even supposing it entirely true (and it is not entirely true, for many facts unite to prove that under like conditions both the quantities and the qualities of sensations and emotions in different individuals differ considerably), by no means implies that what he knows under its subjective aspect as feeling, is, under its objective aspect, nervous action. The average observer has no direct evidence that these other like beings have nervous systems, any more than that he has himself a nervous system; and he has no direct evidence in the one case any more than in the other, that nervous excitations are the causes of feelings. Experi- mental physiologists and pathologists only have proofs; and even their proofs are mostly indirect. The experiments which yield them are usually made on beings of another and much inferior order. The contractions of muscles and arteries, caused by irritating nerve-trunks in frogs, the convulsive movements, and sometimes the sounds, made by birds and mammals whose nerve-centres are variously in- jured— these are the phenomena from which it is inferred that the human nervous system is the seat of the human feelings, and that these feelings are the correlatives of its excitations:, the only important verifications of the inference being those THE DATA OP PSYCHOLOGY.
^jjW.ainecl. during surgical operations where nerve-trunks arc Jkrt through, and those furnished by post mortem examina- tions of morbid nervous structures in the bodies of those who when alive displayed abnormal excesses or defects of feel- ing. 8. And then,, having learnt at second hand, through the remotely-inferential interpretation of verbal signs, that in now one and now another of the bodies he recognizes as like his own there has been found a nervous system, and that the stimulations of this produce those manifestations which in himself accompany feelings, the reader imagines a nervous system contained in his own body, and concludes that his sensations and emotions are due to the disturbances which the outer world sets up at its periphery, and arouses by indirect processes in its centres. Such, stated as briefly as possible, is the long and involved series of steps by which alone the connection between nervous action and feeling can be established.
Nevertheless, the evidence of this connection is so largo in amount, presents such a congruity under so great a variety of circumstances, and is so continually confirmed by the correct anticipations to which it leads, that we can entertain nothing more than a theoretical doubt of its truth. " Hero accepting the belief, alike popular and scientific, that all the human beings known objectively have feelings like those which each knows subjectively; and accepting also the belief, originating with science but now diffused through the general mind, that feelings arc the concomitants of nervous changes; we will proceed to consider the relation between feelings and nervous" changes under its leading aspects, ;.. s^ 42. And first let us observe that the circumstances :< conducive to the one are identical with the circumstances ;, conducive to the other. The^onditions which we. before foundLcssential to the production of servo us action, we shall now find^s^ntial^tp the pioduction of feeling^ We may pass over the evidences briefly as being many of tliera the Inner aspects of phenomena already observed under their outer aspects.
That without continuity of nerve-fibre between periphery and centre,, a disturbance at the one causes no feeling1 at the other, is proved to every one who has cut himself deeply: for a long time the part that has had its nervous com- munication destroyed^ remains numb. This experience, usually very limited in each person, is borne out by the testimony of those seriously injured; and especially by the testimony of those whose sensations over large parts of their bodies have ceased, and who, after death, are found to have lesions in the conducting structures of the nervous centres.
The hindrance or prevention of feeling by pressure, is illustrated by the numbness of a limb so placed that its whole weight, and perhaps the weight of another limb lying over it, comes on the edge say of a table; so that} great stress is borne by some portion of the chief nerve- trunk. Local anaesthesia thus caused in strong persons, is caused still more readily in feeble persons; who, on awaking, not unfrequently find complete insensibility of the parts that have been pressed against the bed daring sleep.
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 ex- tremities. 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 ether- spray. 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 I 102 THE DATA OF PSYCHOLOGY.
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 con- taining 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, pro- duces 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 in- capacity 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 con- tiguity,, 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 conscious- ness are mostly traced in the intensification of those in- ternally-initiated feelings with which we shall deal pre- sently; 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 usu- ally 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 304 THE DATA OF PSYCHOLOGY.
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 allitsbranch- ings. 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 centri- petal 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 ex- perienced, 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 impres- sions 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 occu- pied 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 be- come 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 co- operating 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 mani- festly 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 disturb- ances 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 sub- jective 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 dip- ping the hand into hot-water, or by those which the palate and the nostrils experience from pungent substances mo- mentarily 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 dis- turb 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 pre- ceding 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 or- ganization 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 in- coming 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 completely- formed 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 per- 110 THE DATA OF PSYCHOLOGY.
ceived. A few minutes5 rest partially restores tlie impressi- bility; 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 annoy- ance. The feelings generated by sonorous vibra- tions 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 tempo- rary 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, be- cause they are rendered for a time partially deaf to ordi- nary 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 sensi- bility^ 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 dis- closed, 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 no- thing conspicuous, there will be perceived a transient image of the object, in which the light and dark parts are re- versed. The interpretation of this fact is that those por- tions of each retina on which strong light had fallen, to- gether with the answering portions of the optic centres, having undergone the most change with correspond- ing production of the most feeling, are the next in- stant 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 inca- pacitated, 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.