

ELECTRICAL BREAK-EXCITATION. 107 



great differences here, since usually the exciting current is kept 

 closed for barely a second. 



It is an analogous fact that if with a weak current there is no 

 break-contraction, one occurs if a stronger current, at the opening 

 of which there may have been an excitation, be first passed through 

 the nerve in the same direction. For the nerve is strongly polarised 

 by the last-mentioned current; the quickly following opening 

 of a weak current, which previously had no effect, now elicits 

 a contraction, since there is now a stronger polarisation-current 

 than before. This is also the explanation of the fact that the 

 phenomenon of the 'hiatus' discovered by me, did not appear, 

 or at least not usually, when I changed the current from a higher 

 to a lower strength. Biedermann 1 and Tigerstedt 2 recently ob- 

 served similar facts. 



The strength of the polarisation-current increases, moreover, 

 with the strength of the primary current ; hence it is that at 

 indifferent points in a nerve or muscle break-contractions do not 

 occur until strong exciting currents are employed, and increase 

 with the current strength. 



Tigerstedt has also found that the sciatic nerve of a frog is 

 easier to polarise near the point of section, or after dilute alcohol 

 has been applied to it. Both these conditions also favour the 

 occurrence of break-contractions, as was shown by my earlier 

 experiments, and those of Biedermann. 



The polarisation- current can also be increased by the use of 

 polarisable, instead of unpolarisable electrodes. In this case there 

 is an external polarisation-current between the metal and moist 

 nerve, and an internal one between the various constituents of the 

 nerve. As, however, the closure through the nerve of the external 

 polarisation-current is determined by the same, or nearly the same 

 conditions as determine that of the internal one, and as the former 

 current is added to the latter, a series of phenomena which depend 

 on the closure through the nerve of polarisation-currents are in 

 this case unusually well-marked. It is thus very easy to convince 

 oneself that if instead of unpolarisable electrodes ordinary metallic 

 electrodes are used, and with the same resistance, in order that the 

 conditions may be as like as possible, break-contractions at break 

 of the main-circuit always appear earlier than when unpolarisable 

 electrodes are used. An experiment may be cited to exemplify this. 



1 Wiener Sitzungsberichte, Part iii. vol. Ixxxiii. p. 328, 1881.. 



2 Tigerstedt, p. 55 of this book. 



