374 PSYCHOLOGY. 



particular effect of startling fails to occur if the nerve 

 be cut. 



In general, liowever, the stimulating effects of a sense- 

 impression preponderate over the inhibiting effects, so that 

 we may roughly say, as we began by saying, that the wave 

 of discharge produces an activity in all parts of the body. 

 The task of tracing out all the effects of any one incoming 

 sensation has not yet been performed by physiologists. 

 Eecent years have, however, begun to enlarge our informa- 

 tion ; and although I must refer to special treatises for the 

 full details, I can briefly string together here a number of 

 separate observations which prove the truth of the law of 

 diffusion. 



First take effects upon the circulation. Those upon the 

 heart we have just seen. Haller long ago recorded that 

 the blood from an open vein flowed out faster at the beat of 

 a drum.* In Chapter III. (p. 98) we learned how instan- 

 taneously, 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 Char- 

 pentier, 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 

 Tjlood-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 vol- 

 ume in surprising fashion." t Figure 82 (from Fere X) 



* Cf . Fere . Sensation et Mouvement (1887), p. 56. 

 t La Paura (1884), p. 117. Compare Fere : Sensation et Mouvement, 

 chap. XVII. 



I Revue Pbilosophique, xxiv. 570. 



