CHAP, x.] OF THOUGHT. 437 



that impressions, strong emotions, modify the beatings of the 

 heart, the colouration of the cheeks, &c. (see p. 220). It was this 

 interesting fact which served M. Mosso as a starting-point. He 

 formed the design of finding a practical experimental means of 

 measuring with some precision this influence of the nervous 

 centres upon the vaso-motory nerves. For this purpose he made 

 use of a large glass cylinder, closed at one of its extremities, 

 open at the other, a kind of large cylindrical flask, sufficiently 

 wide to accommodate easily the hand and entire forearm. A 

 large armlet of caoutchouc fixes the tube to the bend of the 

 elbow ; at the same time shutting the upper orifice, while exer- 

 cising only the most moderate compression. The wall of the 

 cylinder is furnished with three orifices. One, which is closed 

 with a stopper, serves to fill the vessel with tepid water. A 

 second opening permits the introduction of the ball of a thermo- 

 meter, which indicates the temperature of the water. To the 

 third is adjusted a curved tube, very analogous to the hsemo- 

 dynamometer of Poiseuille. This tube communicates with the 

 cavity of the cylinder, and is so arranged that a small column 

 of water rises therein. Finally, it is furnished at its upper 

 extremity with a movable needle, adapted to note the oscilla- 

 tions of this column upon the paper of a registering tambour. 

 Things being thus arranged, it is easy to see that the slightest 

 sanguineous afflux in the forearm will diminish the volume of 

 the member, and consequently will cause a part of the liquid 

 column of the hsemodynamometer to flow back into the receiver. 

 Every congestion, every dilation of the vessels will produce 

 an inverse effect. In both cases the needle will write upon 

 the registering paper the oscillations of the liquid column. 



With this apparatus Dr. Mosso has been able to prove that 

 every cerebral phenomenon has its repercussion upon the peri- 

 pheric circulation. The following are the principal facts which 

 he has observed with regard to man during wakefulness and 

 slumber. 



In the waking state, every sensation, every moral or physical 



