THE DISCHARGE HYPOTHESIS. 247 



fibre cannot penetrate through the sheaths, it is clear 

 that the excitement can only act on the muscle- 

 substance where the nerve-substance and the muscle- 

 substance are really in immediate contact — that is, only 

 within the sarcolemma pouch. The nerve-sheath is, as 

 we already know, a real isolator as regards the process 

 of excitement within the fibre ; for an excitement within 

 a nerve-fibre remains isolated in this, and is not trans- 

 ferred to any neighbouring fibre. It is quite impos- 

 sible, therefore, that it can transfer itself to the muscle- 

 substance, since it is separated from the latter not only 

 by the nerve-sheath, but also by the sarcolemma. 



But if the nerve-fibre penetrates the sarcolemma, as 

 appears from the microscopic observations above de- 

 scribed, and if nerve-substance and muscle-substance 

 are in immediate contact, then the transference of the 

 excitement present in the nerve to the muscle substance 

 is intelligible. The argument holds good whether we 

 assume that the nerve, directly after its entrance within 

 the sarcolemma, ends in a nerve -plate or a short nerve- 

 net, or whether, as Gerlach says, it spreads further. All 

 that is needed to make the process of transference in- 

 telUofible is that the two substances should be in imme- 

 diate contact, and so much is granted, whichever view 

 is preferred. But the process, if intelligible, is yet not 

 explained. An attempt at explanation must be based 

 on, and have regard to, all the established facts. 



3. It is natural to think of the electric characters 

 of nerves and muscles, and to seek the explanation in 

 these. In nerves electric tensions prevail which dur- 

 ing the activity of the nerve undergo a sudden decrease, 

 a so-called negative variation. Such sudden variations 

 of electric currents are, we know, able to excite the 



