Chapter XI

, others we shall examine under the heads of Instinct and Emotion--but it innervates the muscles generally. M. Féré has given very curious experimental proofs of this. The strength of contraction of the subject's hand was measured by a self-registering dynamometer. Ordinarily the maximum strength, under simple experimental conditions, remains the same from day to day. But if simultaneously with the contraction the subject received a sensorial impression, the contraction was sometimes weakened, but more often increased. This reinforcing effect has received the name of _dynamogeny_. The dynamogenic value of simple _musical notes_ seems to be proportional to their loudness and height. Where the notes are compounded into sad strains, the muscular strength diminishes. If the strains are gay, it is increased.--The dynamogenic value of _colored lights_ varies with the color. In a subject[355] whose normal strength was expressed by 23, it became 24 when a blue light was thrown on the eyes, 28 for green, 30 for yellow, 35 for orange, and 42 for red. Red is thus the most exciting color. Among _tastes_, sweet has the lowest value, next comes salt, then bitter, and finally sour, though, as M. Féré remarks, such a sour as acetic acid excites the nerves of pain and smell as well as of taste. The stimulating effects of tobacco-smoke, alcohol, beef-extract (which is innutritious), etc., etc., may be

## partly due to a dynamogenic action of this sort.--Of _odors_, that of

musk seems to have a peculiar dynamogenic power. Fig. 85 is a copy of one of M. Féré's dynamographic tracings, which explains itself. The smaller contractions are those without stimulus; the stronger ones are due to the influence of red rays of light.

[Illustration: FIG. 85.]

Everyone is familiar with the _patellar reflex_, or jerk upwards of the foot, which is produced by smartly tapping the tendon below the knee-pan when the leg hangs over the other knee. Drs. Weir Mitchell and Lombard have found that when other sensations come in simultaneously with the tap, the jerk is increased.[356] Heat, cold, pricking, itching, or faradic stimulation of the skin, sometimes strong optical impressions, music, all have this dynamogenic effect, which also results whenever voluntary movements are set up in other parts of the body, simultaneously with the tap.[357]

These 'dynamogenic' effects, in which one stimulation simply reinforces another already under way, must not be confounded with reflex acts properly so called, in which new activities are originated by the stimulus. All instinctive performances and manifestations of emotion are reflex acts. But underneath those of which we are conscious there seem to go on continually others smaller in amount, which probably in most persons might be called fluctuations of muscular _tone_, but which in certain neurotic subjects can be demonstrated ocularly. M. Féré figures some of them in the article to which I have already referred.[358]

* * * * *

Looking back over all these facts, it is hard to doubt the truth of the law of diffusion, even where verification is beyond reach. _A process set up anywhere in the centres reverberates everywhere, and in some way or other affects the organism throughout, making its activities either greater or less._ We are brought again to the assimilation which was expressed on a previous page of the nerve-central mass to a good conductor charged with electricity, of which the tension cannot be changed anywhere without changing it everywhere.

* * * * *

Herr Schneider has tried to show, by an ingenious and suggestive zoological review,[359] that all the _special_ movements which highly evolved animals make are differentiated from the two originally simple movements, of contraction and expansion, in which the entire body of simple organisms takes part. The tendency to contract is the source of all the self-protective impulses and reactions which are later developed, including that of flight. The tendency to expand splits up, on the contrary, into the impulses and instincts of an aggressive kind, feeding, fighting, sexual intercourse, etc. Schneider's articles are well worth reading, if only for the careful observations on animals which they embody. I cite them here as a sort of evolutionary reason to add to the mechanical _a priori_ reason why there _ought_ to be the diffusive wave which our _a posteriori_ instances have shown to exist.

I will now proceed to a detailed study of the more important classes of movement consequent upon cerebro-mental change. They may be enumerated as--

1) Instinctive or Impulsive Performances;

2) Expressions of Emotion; and

3) Voluntary Deeds;

and each shall have a chapter to itself.

* * * * *

[345] Emotions and Will, pp. 4, 5.

[346] Cf. Féré. Sensation et Mouvement (1887), p. 56.

[347] La Paura (1884), p. 117. Compare Féré: Sensation et Mouvement, chap. xvii.

[348] Revue Philosophique, xxiv. 570.

[349] Revue Phil., xxiv. pp. 566-7.--For further information about the relations between the brain and respiration, see Danilewsky's Essay in the Biologisches Centralblatt, ii. 690.

[350] Quoted from the report of Tarchanoff's paper (in Pflüger's Archiv, xlvi. 46) in the American Journal of Psych., ii. 652.

[351] Archiv f. Psychiatrie, vii. 652; ix. 129.

[352] Sensation et Mouvement, 57-8.

[353] R. Accad. dei Lincei (1881-2). I follow the report in Hofmann Schwalbe's Jahresbericht, x. ii. 93.

[354] Cf. Féré, Sensation et Mouvement, chap. xiv.

[355] The figures given are from an hysterical subject, and the differences are greater than normal. M. Féré considers that the unstable nervous system of the hysteric ('ces grenouilles de la psychologie') shows the law on a quantitatively exaggerated scale, without altering the qualitative relations. The effects remind us a little of the influence of sensations upon minimal sensations of other orders discovered by Urbantschitsch, and reported on page 29 of this volume.

[356] Mitchell in (Philadelphia) Medical News (Feb. 13 and 20, 1886); Lombard in American Journal of Psychology (Oct. 1887).

[357] Prof. H. P. Bowditch has made the interesting discovery that if the reinforcing movement be as much as 0.4 of a second late, the reinforcement fails to occur, and is transformed into a positive inhibition of the knee-jerk for retardations of between 0.4' and 1.7'. The knee-jerk fails to be modified at all by voluntary movements made later than 1.7' after the patellar ligament is tapped (see Boston Med. and Surg. Journ., May 31, 1888).

[358] Revue Phil., xxiv. 572 ff.

[359] In the Vierteljahrschrift für wiss. Philos., iii. 294.

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