234 ELECTRIC CURRENT. LiECT. XII. XIII. 



tions re-appear. These alternations may be repeated a cer- 

 tain number of times on the same animal. The intervals 

 of time between the passage of the two currents, depend 

 on the intensity of the current and the vivacity of the 

 animal. 



It is easy to prove that the diminution of the excitability 

 of the nerve from the passage of the current, is principal- 

 ly manifested in the portion traversed by the latter. Sup- 

 pose we have passed a current through the nerve of a frog, 

 prepared after Galvani's method, and have prolonged the 

 action until the contractions have ceased ; if we then apply 

 the conductors to a portion of the nerve more distant 

 from the brain than that on which we first acted, we soon 

 observe the contractions re-appear according to the laws 

 already laid down. By continuing these experiments, 

 exposing successive portions of the nerve more distant from 

 the brain, similar results are obtained. We may therefore 

 say, that the excitability of the nerve, roused by the current, 

 retires towards the periphery according as its vitality be- 

 comes extinct. When we act on a living animal in the way 

 described, we find that the signs of pain evinced when an 

 electric current traverses its nerves, are also manifested 

 when we act on those parts of the latter, nearer and nearer 

 to the brain, according as its vivacity diminishes by the 

 prolonged passage of the current. In both cases, it is the 

 excitability of the nerve which becomes weakened by the 

 passage of the current ; and, as when a muscular mass is 

 traversed by the latter, it is certain that the whole, or at 

 least the greater part of the current passes, not by nervous 

 filaments, but by the muscles, which are better conductors, 

 it is natural that these filaments should preserve their excita- 

 bility, and that they should be found also excitable by the 

 current. 



Effects of the Current on poisoned Animals. It was im- 



