242 ELECTRIC CURRENT. LECT. XII. XIII. 



has been continued for ten or twenty seconds. It does, how- 

 ever, exist: but to appreciate it, it is necessary to proceed 

 more rapidly. If the passage of the inverse current be limited 

 to a small fraction of a second, we find on opening the circuit, 

 a weaker contraction than that which is obtained after the 

 current has circulated for one or more seconds. It is very 

 easy to prove this, by closing the circuit by the aid of a 

 wheel furnished with a metallic tooth, and to which we at- 

 tach one of the wires of the pile during its rotation. When 

 the nerve has lost part of its excitability, we then readily 

 perceive that the contraction manifested on opening the cir- 

 cuit, increases proportionably to the time that the circuit has 

 been closed. The greatest effect of the passage is obtained 

 at the end of fifteen or twenty seconds. It is needless to 

 say, that these effects do not continue to increase on a dead 

 animal. 



Influence of Repose. Finally, it remains for me to notice 

 the influence produced by repose on a nerve which has been 

 submitted to the action of the current. If the nerve has 

 been traversed by the direct current, repose restores a por- 

 tion of its excitability ; if it has been traversed by the in- 

 verse current, it loses by repose a part of that excitability 

 which it had acquired under the influence of the current. 

 When the nerve is very irritable, a very short repose suf- 

 fices to restore the excitability lost by the action of the 

 direct current ; it is the same with the augmentation occa- 

 sioned by the inverse current ; almost as soon as it is inter- 

 rupted, the nerve returns to its normal condition. In pro- 

 portion as the excitability diminishes, the duration of repose 

 necessary for giving or arousing the excitability acquired 

 under the passage of the current,, augments. 



I must here add, that the relation between the muscular 

 contractions and the current is established in a more inti- 

 mate manner, by measuring this contraction and comparing 



