the tubes, according to the speaker's experiments, both ways from any point where the equilibrium has been disturbed; being capable of an almost infinite number of variations or gradations, and of so peculiar a character as to require the unimpaired condition of the nervous structure. "} S6 THE DATA OF PSYCHOLOGY.
a discharge alon<* out-going nerves, it thereupon becomes less capable of emitting such discharges in response to such stimuli. The quantity of molecular motion locked up in a nerve-centre, is measured by the contained quantity of unstable nerve-matter; and decomposition of that part of the unstable nerve-matter which was most favourably placed for beine acted on, leaves not only a diminished rsuantitv but a quantity that is less favourably placed for being* acted on — leaves, therefore, a decreased readiness to undergo change when disturbed, as well as a decreased stock of molecular motion to be liberated. Consequently., other things remaining the same, every excitation of a nerve-centre reduces, for a time,, its impressibility and its energy.
This temporary enfeeblement of a nerve-centre, when caused by moderate action, is inconspicuous. The disinte- grated mass quickly re -integrates itself from the materials brought by the blood. But if the stimulation and con- sequent discharge are violent, or if stimulations and dis- charges are repeated very rapidly, then repair falls so far in arrear of waste that- partial or entire incapacity of the nerve-centre results. All its unstable substance within easy reach of in-coming disturbances has been decomposed; leaving such part only of its unstable substance as is most removed from disturbances, and can be affected only by excessive ones. A well-known experiment on the vaso- niotor system of a frog, may be cited in illustration. If a frog's foot be placed under a microscope, and so adjusted thai the arteries ramifying through the transparent mem- brane between the toes are brought into view, then, if a powerful irritant be applied to this membrane, the first re- sult observed is that these arteries are violently constricted — the strong impression conveyed to the vase-motor centres there liberates an excessive discharge along the fibres supplying these arteries, causing spasmodic contractions of their muscular coats. The second result is that these S STIMULATION AND NERVOUS DISCHARGE. 87 arteries dilate: losing their normal contractility they become distended with blood, and the part is, as we say, congested. That this is due to extreme prostration or tem- porary paralysis of the vaso-rnotor centre, has been clearly proved; for if the nerve-trunk containing the vaso-motor fibres be dissected out and artificially irritated, the dilated arteries instantly contract. How a nerve-centre may be prostrated by a rapid succession of moderate stimuli and discharges, instead of by one violent stimulus and discharge, is shown by the familiar effect of friction on the human skin. A single moderate rub causes only a slight reflex action oa its vessels, and leaves the vaso-motor apparatus ready to act afresh with no apparent diminution of power. But a series of rubs is followed by temporary congestion of the vessels: it is some little time before the vaso-motor centre regains its full control over them. And if the skin be continuously chafed, the excessive waste and debility of the vaso-motor centre entail that enduring redness called congestion. Those parts of the nervous system con- cerned in muscular action, daily illustrate the same general relation. Fatigue is a state in which the ability to generate motion has been greatly diminished by long-continued genesis of motion; and every tired horse shows, by the small response he makes to a cut of the whip, that a more violent impulse must be propagated to the nerve-centres to cause the ordinary evolution of nervous energy.
Irregularities in the manifestation of this truth, are due to that entanglement of the conditions which was indicated at the close of the last chapter. It frequently happens, for instance, that after performing its function for some time, a nerve-centre responds to the demands on it better than at first — a fact apparently at variance with the foregoing con- clusion. But this conclusion supposes all the circumstances to have remained the same; and in such cases they have not remained the same. There has been an exaltation of the heart's action, or a ]ocal increase in the quantity of blood, or £3 TEE DATA OF PSYCHOLOGY.
a more rapid aeration of blood, or all of these. When every appliance which furthers the disintegration and re-integra- tion of a- nerve-centre, has been brought into full play, both waste and repair go on faster; and there result greater impressibility and energy than when the previously-unused centre contained but little blood languidly circulating.
§ 37. Were Life uniform in its rate — were terrestrial con- iditions such that actions of all kinds could be performed as readily at one time as at another, repair and waste of all » organs, including nervous organs, would have to keep an ap- proximately-even pace, one with the other. But the alterna- tion of clay and night entails an alternation of greater and less I facility for actions; and there has resulted in organisms an I adapted alternation in the relative rates of waste and repair. ' The adaptation is manifestly due to survival of the fittest. An animal so constituted that waste and repair were balanced from moment to moment throughout the twenty-four hours, would, other things equal, be overcome by an enemy or competitor that could evolve greater energy during the hours when light facilitates action, at the expense of being less energetic during the hours of darkness and concealment. : Hence there has necessarily established itself that rhythmical ] variation in nervous activity, which we see in sleg]3_ancL i waking. Let us observe how these are interpretable, the one as a state of the nervous centres in which waste has got considerably in excess of repair, and the other as a state in which repair has made up for previous excess of waste.
Confining ourselves to persons whose functional rhythms have not been deranged by undue excitements,, we see that after some sixteen or eighteen hours of sustained impressi- bility and energy, there is a diminished readiness to respond to stimuli that fall on the eyes, ears, and surface of the body at large; and presently this becomes so pronounced that loud sounds and the irritations produced by strained atti- tudes^ fail to evoke movements. When great exertion has STIMULATION AJSTD NERVOUS DISCHARGE. 89 "been gone through, or when previous intervals ot sleep have "been omitted, the decrease of impressibility is such that tickling the nostrils or pinching the skin does nothing more than cause, perhaps., a reflex start. This change, so marked and often so rapidly established,, seems greater than the alleged cause can produce; but it is fully accounted for when we include an indirect effect of this cause. The waste of the nerve-centres having become such that the stimuli received from the external world no longer suffice to call forth from them adequate discharges,, there results a di- minished impulse to those internal organs which subserve nervous activity, including, more especially, the heart. Consequently the nerve-centres, already working feebly, are supplied with less blood and begin to work more feebly — respond still less to impressions, and discharge still less to the heart. And so the two act and re-act until there is reached this state of profound unimpressibility and inactivity.
Between this state and the waking state, the essential j distinction is a great reduction of waste. Certainly in some j nervous centres and probably in all, waste does not abso- 1 lutely cease: there continue those emissions of force which I keep up the vital processes; and it is, I think, unlikely that; there is ever an entire stoppage of those changes which take place in the highest centres. But the rate of waste falls so low that the rate of repair exceeds it. It is not that during 1 the period of activity waste goes on without repair, while I during the period of inactivity repair goes on without waste; ] for the two always sgo on together. Very possibly — probably j even—^repair is as rapid cTurtng" the day as during the night: perhaps even more rapid: for the blood is on the average richer and circulates faster. But during the day the loss is gTeaterJfchan the gain, whereas during the night the gain is clm^ished by scarcely any loss. Hence results accumula- J tion: there is a restoration of the nerve-tissue Jo Litsjtate of;; integrity.
In the course of some hours this restoration begins to 90 THE DATA OE PSYCHOLOGY.
show its effects in returning impressibility. While in sleepiness we see a decreasing readiness to respond to ex- ternal stimuli, the approach to a waking state is character- ized by an increasing readiness to respond to external stimuli. Throughout the period of quiescence the afferent nerves remain subject to incident forces. The pressure of the body on the bed affects some of them., and others are affected by the touch of the bed-clothes; degrees of heat a little above or below the average, act on others; and yet others receive sonorous vibrations constantly occurring. But whereas sleep results because the centres worn by action become less and less sensitive to these stimuli, waking results because the centres repaired during rest become more and more sensitive to them. The strains of muscles and liga- ments which during the first part of the night fail to cause changes of attitude, cause such changes towards morn- ing. The amount of light that traverses the eye-lids pre- sently suffices to call forth movements. Some slight noise which., hours before, would have had no effect, now produces • a start. Even in the absence of external stimuli (which, however, can never be absent) there are the stimuli from the viscera, and especially from the alimentary canal: an empty stomach eventually sends to the cerebro-spmal system enough disturbance to end the quiescent state. The longer repair goes on unopposed by appreciable waste, the greater must become the instability of the nerve-centres, and the greater their readiness to act; so that there must at length come a time when the slightest impressions will produce motions. Such impressions, however slight, are necessary antecedents. The re -integrated nerve-centres do not resume their activity until an impulse arriving from the periphery overthrows some of their molecules. Evidence of this is furnished to most every morning. On awakening from refreshing sleep, there commonly occurs an involuntary stretching of the muscles of the whole body; showing an immense undirected motor discharge. But this is not the KERYOlfs STIMULATION AND NERVOUS DISCHARGE. 91 initial fact. No one awakes to find himself then and tliere stretching; which might happen were the discharge spon- taneous. It conies after those stronger disturbances that are propagated to the centres,, as soon as some slight distur- bance has led to the slight movements that ac company waking*. A trifling sound causes opening of the eyes and a turn of the head. Thereupon follow vivid impressions through the eyes,, through the skin that rubs against the bed-clothes,, and through the muscles that set up the movements. And a relatively -large aggregate of stimuli being sent from the periphery, there results this relatively- large gush of motor excitement.
On pursuing the argument we may understand why the energies continue to rise for some time after awaking. We saw that when once sleepiness has commenced,, it increases because in proportion as the nervous centres fail in their discharges, the heart, losing part of its stimulus, begins to flag, and that the flagging of the heart leads to a greater inertness of the nerve-centres, which, re-acts as before. Conversely, it will here be manifest that when the nerve-centres, repaired by sleep, become again ready for discharging with vigour, there take place an action and re- action which have the opposite effect. The pulsations on awak- ing are comparatively feeble. As soon as stimuli begin to be received through the sensory organs, and the discharges of the nerve-centres are renewed, the heart comes in for its sharo of these and acts more vigorously. By so doing it supplies the nerve-centres with more blood in quicker gushes. A greater nervous discharge is thereby made possible, which again, among other results, exalts the heart's action. And' so the mutual aid goes on: the greatest nervous vigour being reached when the vascular activity has been still further raised by a meal, and the blood has been enriched by the absorbed materials.
§ 88. As implied by much that has gone before, and as 02 THE DATA OF PSYCHOLOGY.
especially implied by the last section, nervous stimulation and nervous discharge have always both special and general results. Beyond the primary and definite effect wrought on a particular part by a particular impression, there are in evervcase secondary and indefinite effects diffused through the •whole nervous system,, and by it through the body at large. It was pointed out (§§ 10, 11) that the simplest nerve-centre puts in relation not afferent and efferent fibres alone; but that through other fibres, cominissural and centripetal, con- nections are made between it and other nerve-centres of the same grade and of a higher grade. Further, we saw that when such a nerve-centre is excited through an afferent nerve, the disengaged molecular motion does not escape wholly along one or more efferent nerves; but that part of it, propagated to higher centres, there sets up supplemen- tary changes. The diffusion does not stop here — remoter parts are reached; and thus the disturbance of a single nerve-fibre, if at all considerable, reverberates throughout the entire nervous system, and affects all the functions con- trolled by it. Digging a pin into the foot may cause a con- vulsive contraction not of the leg-muscles only, but of many other muscles throughout the body. At the same time it may alter the rate of pulsation, and send waves of constriction along the arteries. The excreting structures of the skin may be so affected that a burst of perspiration results; and the actions going on throughout the alimentary canal may be deranged. Such reverberations, which become conspicuous when the disturbances are decided, take place also when they are slight. A more vivid light, causing as it does stronger pulses of change through the optic nerve, increases the rate of respiration; and doubtless the other vital functions are simultaneously exalted. So that each nervous impression, beyond a direct response in the shape of increased action from, one or more organs, calls forth an indirect response in the shape of increased action of the organism as a whole.
NERVOUS STIMULATION AND NER70US DISCHARGE..9-3 Kemembering tliat every instant the disturbance thus echoing throughout all passages of the nervous system is not solitary, but that there are many such disturbances, here arising from pressure there from touch, in this place pro- duced by sound and in that by light, at one part by muscular strain and at another by heat or cold; it will be manifest that, besides the few distinct waves of nervous change working their distinct effects, there are multitudinous indistinct waves, secondary and tertiary, travelling in all directions working their indistinct effects.
§ 39. Since such reflected and re-reflected disturbances everywhere act as stimuli, we must regard the entire nervous system as at all times discharging itself. The unstable molecules of its centres, exposed to this confused reverberation, are liable to be decomposed wherever a concurrence of small waves makes the local agitation con- siderable "y and the molecular motion thereupon disengaged, adds to the centrifugal gush perpetually going on. Rightly to conceive nervous action then, we must think of the con- spicuous emissions of force from parts of the nervous system that are strongly disturbed, as standing out from a vague back-ground of inconspicuous emissions from the whole nervous system, which is slightly disturbed.
To this general nervous disturbance with its consequent general discharge, is probably due a certain general action of the motor organs. No muscles are ever in a state of absolute^ rest. What we distinguish as muscular motion is produced by the greater contraction of some muscles than of others. The others, however, are all slightly contracted; and would severally produce motion were they not balanced or out-balanced by their antagonist muscles. This per-: vading activity of the muscles is called their tonic state.. And while we regard particular contractions as the results of particular nervous discharges, we have good reasons for concluding that this universal contraction is the result 01 THE DATA OF PSYCHOLOGY.
of ilie universal nervous discharge. Here are a few of them. Sleep, as above explained, implies diminished nervous discharge,, special and general. A dimi- nution of the general discharge ought, then, to be shown in a decrease of the tonic contraction. It is so shown. Falling asleep is accompanied by muscular relaxation: though previously the attitude was such that no effort seemed requisite to maintain it; yet that there was some muscular strain, and that it has suddenly become less, is proved by the sliding down of a limb, or of the head, to a more stable position. Certain disorders, as palsy, yield further proof. The flexors and extensors which, when duly contracted, serve by their balanced antagonism to hold a limb steady, cease to do this when the general nervous discharge is not great enough to keep them and all other muscles braced up: in default of sufficient stimulus for both, now one set and now the other fails to put the due check on its opponent. That such shakings are so caused, we see clearly in persons debilitated by over-stimulation; for in them this symptom may be temporarily mitigated, or almost cured, by temporarily in- creasing the general nervous discharge. The drunkard who early in the clay cannot lift his glass without spilling the contents, is able to do this after his brain has been excited by the usual doses of alcohol.
Of course it is not the muscles alone on which this con- tinuous centrifugal gush is expended. Through the inter- mediation of nerves connecting the cerebro-spinal system with the sympathetic system, the viscera receive their share of it. Hence the overflow of nervous energy which, without special solicitations, diffuses itself throughout the motor structures, giving elasticity to the step, and producing the concave bend of the back, the opened-out shoulders, the raised head, £c., has, for its simultaneous results, an accelerated circulation, an invigorated digestion, and an exaltation of the vital processes at large.
r X^RYOTTS STIMULATION AND NEBVOUS DISCHARGE. 05 § 40. Briefly reviewed from a somewhat different stand- point, the following are the leading facts which it concerns us to remember.
Nervous stimulations and discharges consist of waves of molecular change, that chase one another rapidly through nerve-fibres. The stimulus or discharge formed of such waves, arises at some place where unstable nerve-substance lias been disturbed; and is the same no matter what agent caused the disturbance. The successive waves severally travel with a velocity which, though considerable compared with ordinary sensible motions, is extremely slow compared with other kinds of transmitted molecular motions. And each set of waves, while itself caused by the decomposition of unstable nerve-matter, is a means of decomposing other unstable nerve-matter: so generating further and often stronger sets of waves, which similarly chase one another into many and distant parts of the nervous system.
There is a triple rhvthm^ln these nervous stimulations and discharges — each form of rhythm being due to the greater or less incapacity for action which an action produces. We have seen that every wave of %isomeric transformation, passing along a nerve-fibre, entails on it a momentary unfitness to convey another wave; and that it recovers its fitness only when its lost molecular motion has beea replaced and its unstable state thus restored. We have also seen that any portion of grey matter in a nerve-centre, which having been disturbed and partially decomposed has emitted a shock of molecular change, is proportionately incapacitated; and that it recovers its original ability only as fast as it re-integrates itself from the materials brought by the blood. And then there comes the further rhythm constituted by the alterna- tions of sleep and waking — a rhythm having the same origin as the last, and being supplementary to it.
The remaining truth which we have contemplated is that pach special stimulation and the special discharge produced by it, do not together form the whole of every nervons act; 9t> THE DATA OF PSYCHOLOGY.
but that there is always an accompanying general stimula- tion and general discharge. Every part of the nervous system is every instant traversed by waves of mole- cular change — here strong and here feeble. There is a universal reverberation of secondary waves induced by the stronger primary waves, now arising in this place and now in thai: and each nervous act thus helps to excite the general vital processes while it achieves some particular vital process. The recognition of this fact discloses a ranch closer kinsliip between the functions of the nervous system and the organic functions at large, than appears on the sur- face. Though unlike the pulses of the blood in many respects, these pulses of molecular motion are like them in being perpetually generated and diffused throughout the body; and they are also like them in this, that the cen- tripetal waves are comparatively feeble while thb centrifugal waves are comparatively strong. To which analogies must be added the no less striking cue, that the performance of its cEee by every part of the body, down even to the smallest, just as much depends on the local gushes of nervous energy as it depends on the local gushes of blood.
CHAPTER VI.
§ 41. Throughout tlie foregoing chapters nervous pheno- mena have been formulated in terms of Matter and Motion. If from time to time the phrases used have tacitly referred to another aspect of nervous phenomena, the tacit references have formed no parts of the propositions set down; but have * This new word will possibly be condemned as not legitimately com- pounded. The objection that the root from which its prefix is derived, is shorn of its fair proportions, admits, I am. told, of a satisfactory answer: from the proximate root, appeal may be made to the original root, which, following the Greek method of forming derivatives, would admit of the required modification. But to the criticism that the word involves the logical inconsistency of uniting a verb with a noun, there is no such suffi- cient answer. Nevertheless, I deliberately adopt JEstliQ-pliysiology in pre- ference to the more cumbrous and cacophonous ^tEsthesi-pliysiology. A. progressive integration by which the originally-distinct and numerous parts of compound words become fused together, blurred, and some of them lost, is one of the essential processes in the development of language. If man- kind had refrained from the obliteration and di&ftgurement of roots, and parts of roots, language would have continued wholly inadequate for all but its simplest functions. Omitting tho-se formed by onomatopoeia, the best words are those from which long use has worn away all, or nearly all, traces of their origin. We may as well, therefore, begin with abbreviated and modified words when we have to coin them; instead of leaving time to bring about the needful shortening and shaping. Those who, dealing with, words as counters, see that their convenience as counters is the chief con- sideration, will probably coincide in this view; though I suppose it will be wholly disapproved by those who regard words not as counters but as money.
K 98 THE DATA OF PSYCHOLOGY.
been due to lack of fit words: — words free from unfit associa- tions. As already said, the nervous system can be known only as a structure that undergoes and initiates either visible changes; or changes that are representable in terms furnished by the visible world. And thus far we have limited ourselves to generalizing the phenomena which it thus presents to us objectively.
Now, however, we turn to a totally-distinct_a,sgect of our subject. There lies before us a class of facts absolutely without any perceptible or conceivable community of nature with the facts that have occupied us. The truths here toj)e ?set down are truths of wrhichthe very elements are unknown to physical science. Objective observation and analysis fail us; and subjective observation and analysis must supple- ; ment them.
In. other words, we have to_treat_of nervpjj£j^hgaQmena as phenomena of consciousness. The changes which, re- garded as modes of the Non-Ego, have been expressed in terms of motion,, have now, regarded as modes of the Ugo, to be expressed in terms of feeling. Having contemplated these changes on their put sides, we_haye to contemplate