394 



ELECTRO-PHYSIOLOGY 



CHAP. 



much later period by Hermann, to whom we are indebted for 

 the first proof of true galvanic muscular effects produced in the 

 living human subject by the current of action. In supplementing 

 his investigations on the action current in frog muscles, Hermann 

 endeavoured in the first place to demonstrate on a single con- 

 venient group of muscles the anticipated decremental current of 

 action in tetanus. For this purpose he selected the forearm, 

 leading off from the thick part of the flesh, and from the prox- 

 imity of the wrist, by appropriate electrodes. These electrodes 

 consisted of thick ropes, saturated with ZnS0 4 , looped round the 

 parts of the arm as above. Yet the expected (descending) current 

 failed to appear here, as in corresponding experiments on the 

 thigh ; only small and irregular deflections were visible. It 

 thus seemed questionable whether, under the conditions described, 

 there was any development of a decremental action current in 

 human muscle during voluntary excitation. Hermann in con- 

 sequence applied himself, with 

 far greater result, to the task of 

 investigating the phasic action 

 current under the same condi- 

 tions, but with artificial excita- 

 tion from the nerve (2V). As 

 was stated above, a diphasic 

 current may be demonstrated by 



FIG. 1-25. Diphasic action current in the meailS of the I'lieotOine method, 



between every two points of an 

 uninjured muscle, directly or in- 

 directly excited, the first phase being abnerval, the second adner- 

 val, in direction. In consequence of the decrement of the ex- 

 citatory wave in excised muscle, the second phase is distinctly 

 weaker than the first. The arrangement of the experiment is 

 shown in Fig. 125, after Hermann. 



The stimuli must be so strong that vigorous twitches ensue 

 in the muscles of the forearm. The results, which consisted in 

 the appearance of a- diphasic action current, at first descending 

 (atterminal), and subsequently ascending (abterminal), were so 

 regular that Hermann was able to denote this experiment as one 

 of the most certain in electro-physiology, "giving, without ex- 

 ception, better and more extensive results in man than in the 

 frog." The same results were obtained on leading off from the 



human forearm. On the right, an un- 

 polarisable rope electro' l' j . 



