x ELECTROMOTIVE ACTION" IN NERVE 311 



We have farther to examine the reasons brought forward by 

 Griitzner and Tigerstedt (48) for their contention that certain 

 forms, perhaps indeed all opening twitches, produced by negative 

 polarisation currents are really closing twitches. In view of the 

 above, it is evident that this current, when of adequate strength, 

 may play the same part along the continuity of the nerve as the 

 demarcation current at the transverse end, i.e. that it can eventu- 

 ally set up " false " opening twitches. 



And, in fact, Peltier (who in 1836 was the first to observe 

 negative polarisation in the limbs of frogs through which current 

 was passing, and whose investigations formed the starting-point 

 of du Bois-Eeymond's labours in this direction) had already 

 interpreted the opening twitch by the polarisation current. Du 

 Bois-Eeymond, however, stated against this view that " these 

 charges, in order to induce a current through the nerve, required 

 to all appearance a closed circuit, which condition was cancelled 

 by opening it" (23, i. p. 381). Matteucci was also of Peltier's 

 opinion, that the opening twitch could be explained by the 

 (negative) polarisability of the nerve, without, however, adducing 

 any cogent evidence (47).. 



As regards du Bois-Eeymond's objections, their importance 

 is lessened, since it has been established experimentally that 

 the internal short-circuiting of a demarcation current that occurs 

 both in muscle and in nerve is sufficient to discharge an " apparent " 

 break twitch. Under the presumption of adequate intensity, the 

 same phenomenon may be anticipated for the negative polarisa- 

 tion current produced by the exciting current, and it only remains 

 to show experimentally that certain opening twitches may really 

 come about as described above. 



Griitzner (I.e.) set up experiments with the view of determining 

 whether there might not be different modes of appearance of the 

 opening twitch, with indirect excitation of the muscle, according 

 as the polarising heterodromous current is short-circuited at the 

 moment of opening the exciting current by a good external shunt 

 circuit, or, in the absence of such a shunt, short-circuits itself 

 internally in the nerve. And there does actually seem, more 

 particularly with metal electrodes, always to be a difference 

 agreeing with the theory. The opening twitch, i.e., appears much 

 earlier (viz. with weaker exciting currents), or is more pronounced, 

 in the presence of an external shunt for the polarisation current, 



