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 THE DATA OF PSYCHOLOGY.
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 pro- duced, 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 nerve- centre involves waste; and that restoration of the nerve- centre 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 nutri- tion 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 con- trary. "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 fol- low that, when re-integration is slow, the like sounds im- mediately 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 sen- sation indirectly produced through the nerves proceeding in- wards from the skin, some of which are nearly always disturbed by each bodily motion; but it is a sensation directly pro- duced, 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 be- longing to each separate contraction. We are aware with- out 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 feel- ings 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 feel- ing 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. Some- times, indeed, the feelings that go along with discharges into the vaso-motor and sympathetic nerves, are the pre- dominant 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 con- nection between a physical change in the nervous system and the psychical change accompanying it, that we may 116 THE DATA OF PSYCHOLOGY.
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 affirma- tive 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 sub- jective 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 con- nection between feelings and nervous changes is con- ditioned 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 be- tween 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 in- termediate phases the amount of feeling must bear a vary- ing ratio to the amount of nervous change which the act implies. Again, if we assume that what is present to consciousness as a sensation of given strength, is the correlate of a proportionate molecular disturbance in all the nervous structures concerned, how shall we interpret the sensations distinguished as subjective? In sundry ab- normal states, strong feelings of cold or heat are felt throughout the body, though its actual temperature has remained unaltered. As in any case of this kind the total nervous change cannot have been the same as if the skin had fallen or risen in temperature to the degree ordinarily required to produce the feeling, we cannot say that there is a. quantitative equivalence between the amount of nervo?is 'bange and the amount of feeling. The disagreeable smell which, 011 the approacli of a fit, tlie epileptic patient fre- quently complains of, affords a yet better illustration. Here the outer ends of the afferent nerves being undis- turbed, and only certain central structures irritated, the quantity of nervous action is not the same as if the sensation had been generated by an actual smell. More conspicuously still do we see the variability of this rela- tion, when we compare the feelings called efforts with the discharges and muscular strains produced by them under different conditions. If the psychical force known as effort were transformable into a constant quantity of physical force,, then,, in any two cases, equal efforts should produce equal contractions. But they do not. Great exertion in a child fails to evolve from its motor organs the dynamic effect which a small exertion evolves from those of a man. Any one who is fatigued finds that an intenser feeling of strain is requisite to generate a given degree of muscular tension, than when he is fresh. And those pros- trated by illness show us that immense expenditures of feel- ing are needed to perform acts which, during health, need scarcely appreciable expenditures of feeling. Doubtless these differences are partly due to differences in the muscles; which, when undeveloped or when wasted, are excited to smaller amounts of tension by equal amounts of discharge. But we must regard them as partly due to the imperfect development, or the worn state, of the interme- diate motor centres and efferent nerves, in which a given feeling excites a smaller molecular disturbance than when they are finished in struct are and in complete repair — a conclusion enforced by the familiar experience that purely nervous acts, as those of thought, require unusual efforts when the brain is tired.
This variability of the quantitative relation between nervous actions and psychical states, is equally seen when we limit our comparisons to those nervous actions and psychical states which occur in the same individual under 11.5 THE DATA OF PSYCHOLOGY.
tlie same bodily conditions. To show that unlike but equally intense sensations may be produced by peripheral disturbances widely unlike in their amounts,, providing they arise in different external sense-organs, is scarcely possible without comparing the amounts of the incident forces; and this we cannot properly do, since we are here confining our attention to correlations within the organism. We are similarly debarred from going at length into the quantita- tive contrasts between the muscular tensions produced by the same feeling of effort, according as the muscles excited are large or small; for we cannot well establish these con- trasts without measuring the muscular tensions by the external actions they are equivalent to. There is, however, one class of appropriate cases — those in which irritations arising within the organism, set up sensations that cause undirected motor discharges. Violent toothache, for ex- ample, is due to waves of molecular change sent through one or two minute afferent nerve-fibres; but the bodily contortions show us that the feeling so produced, suffices to send waves of molecular change through various large bundles of efferent nerve- fibres, and to contract numerous muscles with much force, To which of these disturbances, centripetal or centrifugal, is the feeling equivalent? We cannot say to both,, for one is many times the other in amount; and we have no reason to say that it is equivalent to one rather than to the other: the rational inference being that- it is not equivalent to either.
To understand the real relations between objective and subjective changes in the nervous system, we need but to recall certain of the conclusions reached in preceding chapters. The essential principle of nervous organiza- tion we have seen to be that the small amounts of mo- tion received, liberate larger amounts, and these again still_ larger amounts. A disturbance in the end of an afferent nerve is multiplied as it traverses the nerve, and the degree of multiplication varies with the length of the nerve; it is much, more multiplied in the first ganglion reached, and increases further in traversing the centripetal nerve; it is again multiplied in the superior centre, to be afterwards augmented in its subsequent centrifugal course; and it is once more multiplied, probably in a far greater degree, in the contractile substance of the excited muscles. Hence the accompanying feeling, which is the subjective aspect of this disturbance at one of its intermediate stages, can be a quantitative equivalent neither of the initial nervous change nor of the terminal nervous change. Moreover, since the multiplication varies in degree, being much greater in the organs of the higher senses than in those of the lower, it follows that the ratio between the amount of feeling and the amount of initial change is far from constant; and the evidence clearly indicates a like inconstancy of the ratio between the amount of feeling and the amount of terminal change, according as one or other muscle or set of muscles is made to act.
How then can there be any quantitative relation, it will be jisked. If there is no equivalence between a disturbance set up at the periphery and the produced feeling, and no equivalence between the produced feeling and the motor discharge that follows — if the feeling does not even bear the same ratio to either the initial or the terminal nervous change in different cases; what quantitative relation can there be? The reply is simple. There is a quantitative relation between nervous change and feeling when all other things rernsin the same; and there is a quantitative relation between feeling and resulting contraction when all other things remain the same. Supposing every condition to continue unaltered, then the stimulus conveyed through a given nerve to a given centre, will evoke a feeling that increases and decreases in something like the same pro- portion as the stimulus increases and decreases; and, sup- posing a given muscle to be contracted, then the amount of its contraction will bear a tolerably constant ratio to 120 THE DATA OP PSYCHOLOGY.
the feeling of effort that accompanies the contraction of it. The nature of these correlations may best be expressed by numbers. If, coming through a given afferent nerve, a disturbance represented by 1 generates a feeling repre- sented by 5, then disturbance 2 will generate feeling 10, and disturbance 5 feeling 25; and if, acting through a given efferent nerve, feeling 5 results in muscular tension 60, feeling 10 will result in muscular tension 120. But to complete this numerical expression of the facts we must suppose these ratios to vary with every set of afferent nerves and every set of efferent nerves. If we say that 1 to 5 represents the ratio of disturbance to feeling in the sense of touch, then to represent it in the sense of hearing will need, say, 1 to 100, and in the sense of sight perhaps I to 1,000; and similarly with the ratios throughout the motor apparatus, according as the muscles are large or small.
; In brief, then, the quantitative correlation of feeling i and nervous change, holds true only within narrow limits. (We have good reason to conclude that at the particular place in a superior nervous centre where, in some mys- terious way, an objective change or nervous action causes a subjective change or feeling, there exists a quantitative equivalence between the two: the amount of sensation is proportionate to the amount of molecular transformation that takes place in the vesicular substance affected. But there is no fixed, or even approximate, quantitative relation between this amount of molecular transformation in the sentient centre, and the peripheral disturbance originally causing it, or the disturbance of the motor apparatus which it may eventually cause.
j § 48. The feelings called sensations have alone been con- Isidered thus far; leaving out o?' view the feelings cGs- Itinguished as ^is^ion^Tfluch less definite as they are, land not capable^oFTJeing made at will the objects of obserration and experiment, the emotions are more difficulty to deal with. But having discerned certain general laws to which the simpler feelings conform,, we may now ask •whether, so far as we can see,, they are conformed to by the more complex feelings. We shall find that they are.
The conditions essential to the one are essential to the other. Emotions, like sensations, may be increased or decreased in intensity by altering either the quantity or the quality of the blood. That general abundance of blood is a cause of emotional exaltation, though tolerably certain, is not easily proved; but there is sufficient evidence of the converse fact that, other things equal, depletion is a cause of apathy. The effect of local abundance of blood is undoubted: there is no question that, within limits, the amount of emotion varies as the amount of blood supplied to the great nervous centres. That nervous stimulants in- tensify the emotions, or, as we say, raise the spirits, is even more manifest than that they make the sensations keener. And it is a familiar truth that sedatives diminish what is distinguished as moral pain, in the same way that they diminish pain arising in the trunk or limbs.
That a feeling lasts an appreciable time, is no less true of an emotion than of a sensation: indeed the per-; sistence is relatively conspicuous. The state of conscious- - ness produced by a flash of lightning, is so brief as to seem instantaneous: only by the help of artificial tests are sensations of this kind found to have measurable durations. But no such tests are needed to prove that emotions con- tinue through appreciable periods. Even a simple emotion, as of angj3£ or fear, does not reach its full strength the moment the cause presents itself; and after the cause is removed it takes some time to die away. When hereafter we deal with the origin of emotions, and recognize the fact that they are of far more involved natures than sensa- tions, and imply the co-operation of extremely intricate 122 THE DATA OF PSYCHOLOGY.
nervous structures, we shall understand how this greater duration is necessitated.
Tliat an emotion, like a sensation, leaves behind it a tern- porary incapacity, is also true; and as the emotion produced by a momentarv cause lasts longer than a sensation pro- duced by a momentary cause, so does the partial incapacity for a like emotion last longer than the partial incapacity for a like sensation. Passions of all kinds come in gushes or bursts. That they often continue for hours and days, is true; but they are never uniform throughout hours and days. Be it in grief, or joy, or tenderness, there is always a succession of rises and falls of intensity — a paroxysm of violent feeling with an interval of feeling less violent, followed by another paroxysm. And then, after a succession of these comparatively -quick alternations, there comes a calm — a period during which the waves of emotion are feebler: succeeded, it may be, by another series of stronger waves. As in the case of the sensations so in the case of the emotions, this follows from the fact that what is objectively a nervous action and subjectively a feeling, involves waste of the nervous structures concerned. The centres which are the seats uf emotions undergo dis- integration in the genesis of emotions; and, other things remaining equal, thereupon become less capable of generating emotions until they are re-integrated. I say, other things remaining equal, because the^jrise of jm._emption brings blood to the parts implicated, and so long as the afflux is increasing the intensity of the emotion may in- crease, notwithstanding the waste that has taken place; but the several conditions on which activity depends having become constant, a diminished capacity for emotion inevit- ably follows each gu^F*oi*^motion.
That daily rises and falls of strength, consequent on daily periodicities of waste and repair, occur in the emotions as in the sensations, is also tolerably mani- fest. Cultivated people, mostly leading lives that exercise their bra'ns too much and their muscles too little, and placed in social conditions that commonly bring- the strongest excitements towards the close of the day, are subject to an abnormal periodicity. But those whose lives conform best to the laws of health, exhibit early in the day a general joyousness and emotional vivacity greater than they do towards its close, when approaching sleepi- ness is shown by a flagging interest in the things and actions around.
These complex feelings that are cent-'ally initiated are also like the simple feelings that are peripherally initiated, in having general discharges as well as special discharges: indeed their general discharges are the more conspicuous of the two. A sensation is often visibly followed only by local movement: unless very strong its effect on the organ- ism as a whole is unobtrusive. But an emotion, besides the more obvious changes it works in the muscles of the face, habitually works changes, external and internal, throughout the body at large. The respiration, the circula- tion, the digestion, as well as the attitudes and movements, are influenced by it even when moderate; and everyone knows how strong passions, pleasurable or painful, pro-. foundly disturb the whole system.
§ 49. Nothing has yet been said about the most con- spicuous and most important distinction existing among the feelings. Every feeling, besides its minor variations of intensity, exists under two strongly-contrasted degrees of intensity. There is a vivid form of it which we call an actual feeling, and there is a faint form of it which we call an ideal feeling, What is the nature of this difference as interpreted from our present stand-point?
When studying nerve-structure, we saw that, in addition to connections formed by grey matter between the central ends of afferent and efferent nerves, these have connec- tions with centripetal and commissural nerves, \rfiicli 12-i THE DATA OF PSYCHOLOGY.