NEGATIVE VARIATION OF THE MUSCLE-CURRENT. 205 



extracted is quite certain. E. du Bois-Keymond showed 

 this in the human subject in the following way. The 

 ends of the wire of the multiplier are connected with 

 two vessels filled with liquid, and the index finger of 

 both hands is dipped in these vessels, as in fig. 56. 



FIG. 56. DEFLECTION OK THE MAGNETIC NEEDLE BY THE WILL. 



A rod arranged in front of the vessel serves to steady 

 the position of the hands. Currents are then present 

 in the muscles of both arms and of the breast, which, 

 since the groups of muscles are symmetrically arranged, 

 cancel each other, acting one on the other. If for any 

 reason any current remains uncancelled, it may be 

 compensated in the way before described. When all 

 is thus arranged, and the man strongly contracts the 



