PRODUCED BY A CONSTANT CURRENT. 45 



local change of excitability in the nerve, but on the decrease or 

 increase in strength of the excitation during its propagation along 

 the nerve to the muscle. 



li still remains then to examine whose theory, Pfliiger's or 

 Hermann's, best agrees with the facts, so far as they are at 

 present known to us, relating to the changes in extent of the 

 muscular contractions while a constant current is passing along 

 the nerve. 



In this connection special weight must be assigned to the above 

 recorded experiments on the character of the muscular contractions 

 when with an ascending current the nerve was stimulated close to the 

 positive pole and inside it, and to those where with a descending 

 current it was stimulated quite close to the negative pole. 



These experiments have shown that, if the stimulus is made to 

 operate near enough to the pole, the muscular contractions decrease 

 in the former case under the influence of the polarising current, 

 however weak it may be, and increase in the latter case however 

 strong the polarising current. 



According to Hermann's theory, the negative pole must be sup- 

 posed to exert an inhibitory action on the propagation of the excita- 

 tion, otherwise it could not explain the reason of the diminution and 

 cessation of contraction when with a strong ascending current the 

 nerve is stimulated above the negative pole. Here an experimen- 

 tum crucis seems possible. If this phenomenon depends on inhibi- 

 tion, not at the positive, but at the negative pole, then plainly the 

 effect of such inhibition should be to weaken and finally to annul the 

 muscular contractions when the nerve is stimulated inside the pole 

 with the current descending, provided that the intensity of the 

 current is sufficiently great. This, however, is not the case. If 

 with a descending current the nerve is stimulated sufficiently near 

 the negative pole, the muscular contractions do not disappear, even 

 when a polarising current of 10 Meidinger's elements is applied. 

 They increase, on the contrary, and this to such a degree, that a 

 strength of stimulus which before closure evoked no contractions 

 at all, is now, under the influence of the current, able to evoke 

 maximal contractions. 



Not only therefore does the negative pole exert no inhibi- 

 tory action on the propagation of a stimulus to the muscle, but, 

 quite the reverse, the excitability of the nerve is very considerably 

 increased. 



On the other hand, a much smaller strength of current is sufficient 



