122 THE SIGNS OF LIFE [LECT. 



celebrated " willkiirversuch," by which he considered that he 

 had demonstrated on the normal human subject the electrical 

 effects of voluntary muscular contraction, and I think you may 

 be interested to see the actual figure by which he illustrated 

 the experiment (Fig. 52). 



The usual criticism quoted of this experiment is that of 

 Hermann, who explains the deflection observed in du Bois- 

 Reymond's experiment as being the effect of a secretion current 

 provoked in the skin of the contracting side. He says that 

 in the skin of that side such current will be directed from 

 without inwards, giving current ascending in the active arm. 



This criticism is based upon observations by Hermann 

 and Luchsinger concerning the effects of atropine on the 

 sweat currents of cats, and he expresses himself as follows : 

 " A curarised man could give the du Bois current in the 

 absence of muscular contraction. In the case of an atropinised 

 man it would be absent, in spite of the presence of muscular 

 contraction." * 



I do not myself think that the alternative explanation is 

 necessary. To my mind, du Bois-Reymond's experiment does 

 not demonstrate the existence of contraction currents on man ; 

 nor do Hermann's experiments on cats show that du Bois' 

 currents on man are secretion currents. Neither the contraction 

 current nor the secretion current has been separately obtained 

 on man ; the currents that we have witnessed are susceptible 

 of a far simpler explanation. 



I think they are simply capillary currents arising at the 

 surface of separation between salt solution and skin. Let me 

 show you a couple of experiments in point. 



Instead of dipping the two fingers simultaneously, I will dip 

 them successively, so that the skin of one finger may be pretty 

 completely soaked when the skin of the second finger com- 

 mences to be moistened. There is no deflection so long as 

 only one finger is introduced, but on introduction of the second 

 finger there is current through the galvanometer from the first 

 to the second finger, therefore through the body from the second 



* Hermann, Handbuch, vol. i., p. 225. 



