216 ELECTRO-PHYSIOLOGY CHAP. 



only, the possibility of bipolar excitation with stronger induction 

 currents is indicated by these experiments. The excitation at 

 the kathode must, of course, be regarded as a closing, that at the 

 anode as an opening, excitation. 



We have already seen that the direction of current, with 

 true longitudinal passage through a muscle with parallel fibres, 

 would theoretically have no effect upon the consequences of stimula- 

 tion, but that the sartorius in this very respect gives a varying 

 reaction, owing, no doubt, fundamentally to its asymmetrical 

 structure, and the consequent difference in current density at 

 either end. On careful gradation of current intensity with the 

 rheochord, it may be seen in every case that the closure of the 

 descending current regularly produces the first excitation in the 

 longitudinally traversed sartorius ; it is only with greater intensity 

 of current that the closure of the ascending current also becomes 

 effective ; a more or less evident difference in favour of the 

 downward direction of current is still noticeable in many cases. 

 As a rule, however, this difference, which is at first conspicuous, 

 grows less and less, until at last with stronger currents it becomes 

 imperceptible. The opposite effect occurs with the break excita- 

 tion, to which the ascending direction of current is favourable. 

 The point of the greatest density of current is found on sending 

 current longitudinally through the sartorius at the lower end of 

 the muscle, and corresponds with descending direction of current 

 to the point at which it leaves, with ascending current to 

 the point at which it enters, the muscle-substance. Since in the 

 former case the closure twitch, in others the opening twitch, 

 appear earliest, these facts alone show the probability though 

 only for currents of not too great in tensity that the closing 

 excitation proceeds from the kathode, the opening excitation from the 

 anode (24). 



Again, with respect to the duration of the latent period, the 

 difference in density at the two ends of the longitudinally 

 traversed sartorius is very conspicuous. This is as true of the 

 make as of the break excitation, the latent period being in fact 

 invariably shorter when the excitation starts at the lower (knee) 

 end of the muscle, provided the strength of current in both cases 

 is uniform (Fig. 87, a, I). Tigerstedt subsequently obtained 

 the same results (2, p. 185 ff.) 



In view of the fundamental importance of the law of polar 



