142 PHYSIOLOGY OF MUSCLES AIs'D KERVES. 



in two such entirely similar cases. The difference 

 between the two cases consists solely in the fact that 

 in the latter the katelectrotonic point examined is 

 situated immediately next to the muscle, so that its 

 condition of excitability can be indicated directly by 

 the muscle ; while in the case first observed, the con- 

 dition of excitability at the point e /, before it can find 

 expression in the muscle, must find means of passing 

 through the otherwise altered portions c d and a h. Now 

 it may, on the other hand, be shown that transmission 

 in a nerve under the influence of electrotonus really 

 takes place at an altered speed. In the katelectrotonic 

 portion the rate of propagation is but little altered — 

 is, perhaps, slightly increased; but in the anelectro- 

 tonic portion it is markedly decreased. From this it 

 may be inferred that anelectrotonus not only decreases 

 the excitability, but also hinders the propagation of the 

 excitement; and that where the anelectrotonus is strong, 

 propagation is even entirely prevented. 



6. This not only explains the apparent exception to 

 the laws of electrotonus, but also affords explanation of 

 the fact that strong ascending currents, when closed, 

 are followed by no pulsations. We know that a strong 

 electric current induces katelectrotonas in the upper 

 half, anelectrotonus in the lower. According to Pfliiger's 

 hypothesis, excitement occurs in the nerve only at the 

 point at which katelectrotonus intervenes ; that is, on 

 the closing of the ascending current, in the upper por- 

 tion of the nerve. In order to reach the muscle, this 

 excitement must pass through the lower portion of the 

 nerve, and as this is strongly anelectrotonic, it presents 

 an obstacle to the further passage of the excitement. 

 The excitement which occurs in the upper half is, there- 



