HERMANN VON HELMHOLTZ 



the living, and the electromotive force has its seat 

 in the demarcation zone between the living and the 

 dying. To this he adds a rider, that not only death, 

 but irritation as well, causes the affected substance to 

 become negative to the unaffected portion. He 

 further shows that the really important electrical 

 phenomenon is the negative variation, that is the 

 current flowing in the reverse direction when the 

 muscle is caused to contract, now called the action 

 current. Still it must be observed that Hermann's 

 statement is no final explanation. It does not explain 

 why the dying muscle becomes negative to the living, 

 and it is possible that again we may be obliged to have 

 recourse to some such hypothesis as that of Du Bois 

 Reymond. 



Helmholtz, when he was showing electrical experi- 

 ments of this nature to his audience of students at 

 Konigsberg, hit upon the device (not original, how- 

 ever) of attaching a bit of silvered glass to the astatic 

 needle of his galvanometer, and by this means he 

 reflected a beam of light on a screen, thus making it 

 possible to see at a distance the smallest movement of 

 the needle. This method was independently employed 

 for the galvanometer and electrometer by Thomson 

 (now Lord Kelvin), and it has adaptations well known 

 in every laboratory. It was about this time also 

 that he perfected the arrangements for equalising the 

 opening and closing shocks of the induction coil 

 described in chapter iv., p. 36. 

 no 



