Chapter III

. (Vol. I. p. 98) we learned how instantaneously, according to Mosso, the circulation in the brain is altered by changes of sensation and of the course of thought. The effect of objects of fear, shame, and anger upon the blood-supply of the skin, especially the skin of the face, are too well known to need remark. Sensations of the higher senses produce, according to Couty and Charpentier, the most varied effects upon the pulse-rate and blood-pressure in dogs. Fig. 81, a pulse-tracing from these authors, shows the tumultuous effect on a dog's heart of hearing the screams of another dog. The changes of blood-pressure still occurred when the pneumogastric nerves were cut, showing the vaso-motor effect to be direct and not dependent on the heart. When Mosso invented that simple instrument, the _plethysmograph_, for recording the fluctuations in volume of the members of the body, what most astonished him, he says, "in the first experiments which he made in Italy, was the extreme unrest of the blood-vessels of the hand, which at every smallest emotion, whether during waking or during sleep, changed their volume in surprising fashion."[347] Figure 82 (from Féré[348]) shows the way in which the pulse of one subject was modified by the exhibition of a red light lasting from the moment marked _a_ to that marked _b_.

[Illustration: FIG. 82.]

[Illustration: FIG. 83.--Respiratory curve of B: _a_, with eyes open; _b_, with eyes closed.]

_The effects upon respiration_ of sudden sensory stimuli are also too well known to need elaborate comment. We 'catch our breath' at every sudden sound. We 'hold our breath' whenever our attention and expectation are strongly engaged, and we sigh when the tension of the situation is relieved. When a fearful object is before us we pant and cannot deeply inspire; when the object makes us angry it is, on the contrary, the act of expiration which is hard. I subjoin a couple of figures from Féré which explain themselves. They show the effects of light upon the breathing of two of his hysteric patients.[349]

[Illustration: FIG. 84. Respiratory curve of L: _a_, with yellow light; _b_ with green light; _c_, with red light. The red has the strongest effect.]

_On the sweat-glands,_ similar consequences of sensorial stimuli are observed. Tarchanoff, testing the condition of the sweat-glands by the power of the skin to start a galvanic current through electrodes applied to its surface, found that "nearly every kind of nervous

## activity, from the simplest sensations and impressions, to voluntary

motions and the highest forms of mental exertion, is accompanied by an increased activity in the glands of the skin."[350] _On the pupil_ observations are recorded by Sanders which show that a transitory dilatation follows every sensorial stimulus applied _during sleep_, even if the stimulus be not strong enough to wake the subject up. At the moment of awaking there is a dilatation, even if strong light falls on the eye.[351] The pupil of children can easily be observed to dilate enormously under the influence of _fear_. It is said to dilate in pain and fatigue; and to contract, on the contrary, in rage.

As regards _effects on the abdominal viscera_, they unquestionably exist, but very few accurate observations have been made.[352]

The bladder, bowels, and uterus respond to sensations, even indifferent ones. Mosso and Pellicani, in their plethysmographic investigations on the bladder of dogs, found all sorts of sensorial stimuli to produce reflex contractions of this organ, independent of those of the abdominal walls. They call the bladder 'as good an æsthesiometer as the iris,' and refer to the not uncommon reflex effects of psychic stimuli in the human female upon this organ.[353] M. Féré has registered the contractions of the sphincter ani which even indifferent sensations will produce. In some pregnant women the fœtus is felt to move after almost every sensorial excitement received by the mother. The only natural explanation is that it is stimulated at such moments by reflex contractions of the womb.[354] That the glands are affected in emotion is patent enough in the case of the tears of grief, the dry mouth, moist skin, or diarrhœa of fear, the biliary disturbances which sometimes follow upon rage, etc. The watering of the mouth at the sight of succulent food is well known. It is difficult to follow the smaller degrees of all these reflex changes, but it can hardly be doubted that they exist in some degree, even where they cease to be traceable, and that all our sensations have some visceral effects. The sneezing produced by sunshine, the roughening of the skin (goose-flesh) which certain strokings, contacts, and sounds, musical or non-musical, provoke, are facts of the same order as the shuddering and standing up of the hair in fear, only of less degree.

_Effects on Voluntary Muscles._ Every sensorial stimulus not only sends a special discharge into certain particular muscles dependent on the special nature of the stimulus in question--some of these special discharges we have studied in