392 



ELECTRO-PHYSIOLOGY 



CHAP. 



causes an effect in the direction of an ascending current 

 in the arm, which, according to the later measurements of 

 Hermann, has a very low potential (0'0014 0'0023 Dan.) 

 An analogous result is obtained on leading off from both feet. 

 In order that the experiment may succeed it is essential that the 

 voluntary muscular action should be as vigorous as possible. Du 

 Bois-Eeymond strained his arm until " the muscles appeared as 

 hard as boards, the arm shook violently, and after some seconds 

 a lively sensation of warmth was experienced." Sometimes, as 



Fia. 124. Du Bois' "voluntary experiment." (Du Bois-Reymond.) 



proposed by Mousson, a battery was formed by the co-operation 

 of several persons, a vessel of concentrated salt solution being 

 placed between two, into which each person dipped a finger, and 

 simultaneously stretched one arm (on the same side). All these 

 galvanic manifestations were characterised by a long after-effect, 

 as well as by inability to evoke secondary excitation in the 

 physiological rheoscope, to which we shall return later. This fact 

 in itself is in no way prejudicial to du Bois-Eeymond's dictum that 

 the effect under discussion is the expression of the negative 

 variation of the muscle current in the human limb. 



On the other hand, various other considerations have been 



