332 ELECTRO-PHYSIOLOGY CHAP. 



opening the deriving circuit. A maximum difference of electrical 

 potential in the points of the muscle, from which the electrodes 

 lead off; as well as lead in, is the only indispensable condition. 

 In view of the preceding discussion, there can be no doubt 

 that the striking difference of effect on breaking the circuit at 

 two different points, is solely due to the fact that the demarca- 

 tion current in the one case finds an external circuit of com- 

 paratively low resistance on opening the battery current, which 

 is wanting in the other case. The twitch, though coincident 

 in time with the moment of breaking the circuit, cannot 

 be regarded as a true opening twitch due to internal reaction 

 of the muscle, but is much rather a closure twitch, discharged 

 by external short-circuiting of the muscle current (Bieder- 

 mann, 6). 



If the distance between the two electrodes is very small, 



there will, as a rule, even with minimal currents, be hardly any 



perceptible difference in the magnitude of the break twitches, 



whether the battery circuit or the muscle circuit is opened. 



Intermediate electrode points may be found, in which there is a 



certain difference in the magnitude of twitch, according as it is 



discharged at break of the principal, or deriving, circuit, since 



in the latter case it decreases in proportion as the point of 



entrance of the atterminal battery current recedes from the limit 



of the thermic section, the kathodic contact at the cross-section 



remaining unaltered. This is easily explained in view of the 



pronounced internal short-circuiting of the muscle current that 



always occurs in the immediate vicinity of the electromotive 



surface. For if countless lines of current pass out at the surface, 



in parts that are still excitable, near each transverse section of 



each single primitive fibre, and thus of the entire muscle, a 



battery current entering at this region of internal short-circuiting 



must ipso facto compensate a portion of these lines of current, 



some completely, some imperfectly, while others again may be 



over-compensated. This, however, implies that those spots more 



or less entirely lose their character as kathodic points of the 



muscle current, or even become anodic points of the battery 



current. If the latter is opened again, the former condition 



is instantly recovered ; the points once more become kathodic 



points of the muscle current, and are excited by it. The 



battery current therefore abolishes in part the internal closure 



