in ELECTRICAL EXCITATION OF MUSCLE 287 



with the polarising battery current, may therefore be explained 

 as the summation of two intrinsically inadequate stimuli, and 

 the increased response at the kathode appears to be not so 

 much a peculiar effect of current introductory to the excitatory 

 process as the actual result of that process. This theory is quite 

 compatible with the contradictory behaviour of a muscle during,- 

 and immediately after, protracted weak polarisation, or with the 

 application of stronger currents. 



The after-effects observable in the last case were referred 

 above to local " fatigue " of the kathodic points of fibres, induced 

 by current. The facts before us show that almost immediately 

 after closure of a medium current there is, according to the 

 duration of closure, a progressive diminution, or even complete in- 

 hibition, of response to induction currents at the kathode. The 

 direct dependence of the depression of excitability during the 

 passage of the current upon its duration, with low polarisation 

 intensity, makes it highly probable that in this case the excitatory 

 process itself, or, more correctly speaking, the fatigue induced by 

 the same at the seat of direct excitation, must be regarded as the 

 cause of the decreased, response at the kathode. 



The protracted condition of weak excitation at the kathode 

 gradually produces alterations in the contractile substance of the 

 muscle, as expressed not merely during closure of the current, 

 but also for some time after it has been broken, in a diminished 

 excitability, which is usually explained as a fatigue effect. It 

 in ust be asked, however, how the diminution of response at 

 the kathode immediately after the closure of stronger currents 

 is to be understood and explained. Here there can be no ques- 

 tion of " fatigue " in the ordinary sense of the word, because no 

 conspicuous after-effect outlasting the stimulus can, as a rule, be 

 demonstrated, owing to the brief duration of closure. 



That it is not wholly wanting is shown by the fact that in a 

 series of twitches produced by closing the constant current at 

 short intervals, its direction remaining unaltered, the height of 

 each twitch is perceptibly lower than that which immediately 

 precedes it ; this insignificant after-effect of a single short closure 

 would not, however, suffice to explain the continuously marked 

 depression of excitability at and during closure of the same 

 current. An induction current which produces maximal twitches 

 in the muscle not traversed by the constant current is totally 



