VII. 



DU BOIS' EXPERIMENT 



121 



left hand connected with the S terminal, and my right hand 

 with the N. The forefinger of each hand dips in salt solution, 

 there is little or no difference of potential between my two 

 hands, and the spot is at rest. 



FlG. 52. Du Bois-Reymond's " Willkurversuch," to demonstrate a negative 

 variation during voluntary muscular contraction. The current is ascending in 

 the active arm. (From du Bois-Reymond's Thierische Elektncitaf). 



I now firmly contract the muscles of my right forearm ; 

 the spot moves to my right (your left), or clockwise in the 

 circuit, or in my body from right to left. The spot is " pulled." 



Now I contract the muscles of my left forearm, and every- 

 thing is reversed. You have witnessed du Bois-Reymond's 



