IY. 



INTRODUCTION. 



IN a research carried on in conjunction with P. Moschner, 

 student of medicine *, I found that, in a large number of cases, the 

 excitatory effect of break of a current passing through a nerve or 

 muscle was in reality due, not to the disappearance, but to the 

 appearance of the current : that there is thus a series of apparent 

 break-excitations which are in reality make-excitations. These 

 cases occurred when nerve-currents were present in the piece of 

 nerve experimented on. As is well known, nerve-currents are of 

 considerable magnitude in the neighbourhood of the cross-section, 

 and have a most important influence on the effects of excitation. 

 If, for instance, the nerve-current and the exciting current were in 

 the same direction if, that is to say, I excited with so-called 

 ' like ' currents exceedingly weak currents sufficed to produce 

 very great effects. If, on the other hand, I excited with ' counter- 

 currents,' it was necessary to use very strong currents to elicit any 

 response at all. When there was any response, it was far smaller 

 other things being equal, than in the first case. 



Excitation with counter-currents led us to a peculiar phenomenon 

 hitherto unknown the ' hiatus' in the series of apparent break- 

 contractions. If one electrode was at the cross-section and the 

 other a few mm. (5 to 7) away from it, and the nerve was excited 

 with an ascending current, whose strength was gradually raised 

 from zero, the following phenomena were observed. The break- 

 contractions first increased in size: as the current strength was 



1 Pfliiger's Archiv, vol. xxviii. p. 130. 



