ix ELECTRICAL EXCITATION OF NERVE 151 



the electrical current, in the" one case at the kathode, in the 

 other at the anode. 



A law which appears to hold for all excitable substances 

 depends upon the fact that, after prolonged or repeated closure 

 of a battery current, with unaltered position of electrodes and 

 direction of current, the effect of the closure excitation declines 

 more and more, and finally fails altogether. We have already 

 pointed out for muscle that this depends not upon a gradually 

 developing inexcitability of the entire tract traversed by current, 

 but upon a local alteration of that point (or points) at which the 

 excitatory process was discharged primarily, and indeed during 

 the entire closure of the current, i.e. the physiological kathode. 

 The simplest proof of this is given in the fact that the muscle 

 reacts vigorously on reversing the current, as a rule even 

 more vigorously than before. The same is true of indirect 

 excitation of the muscle from the nerve. Volta, and after him 

 Marianini, came to the conclusion that each direction of current 

 diminished excitability towards itself, and raised it for the opposite 

 direction. " For if current is led through a galvanic prepara- 

 tion so that one leg is traversed in the ascending, the other 

 in the descending direction, the twitches will gradually die out 

 in both legs according to the duration of closure of the current. 

 On reversing the current, lively contractions reappear in both 

 muscles." This phenomenon is termed " the Voltaic Alternative " 

 (supra). Rosenthal (26) has recently made the facts relating to 

 it the subject of a thorough investigation, the results of which 

 are summed up in the observation, " Every constant current that 

 traverses a motor nerve for any length of time throws it into a 

 state of increased excitability to the opening of the same, and 

 closure of the opposite, current, of diminished excitability to the 

 closure of the former and opening of the latter" Ritter pointed 

 out that the opening tetanus disappeared, and the muscle 

 became relaxed instantaneously, when the battery current was 

 closed in the same direction as before, just as in direct excita- 

 tion of the muscles the anodic persistent opening contraction is 

 suppressed by closure of the homodromous current. Rosenthal 

 adds that closure of the current in the opposite direction not 

 merely fails to abolish Ritter's tetanus, but even increases it con- 

 siderably ; while opening of the circuit acts like closure of the 

 homodromous current, i.e. neutralises the tetanus. An extinguished 



