244 ELECTRIC CURRENT. LECT. XII. XIII. 



excite no farther contractions. With the inverse current 

 we obtain the contraction by the spark at the opening of 

 the circuit, because, in the interval of its passage, the ex- 

 citability of the nerve has increased. This augmentation 

 disappears immediately the current ceases to act, and this 

 is the reason why the spark no longer excites contractions 

 when we subsequently again close the inverse circuit. 



With these notions we can understand the fact of the 

 voltaic alternatives : when a nerve has been for some time 

 traversed by the direct current, and has lost its excitability, 

 it no longer suffers contraction, notwithstanding that there 

 may be a spark at the closure, and at the interruption of 

 the current. The inverse current restores to the nerve a 

 portion of its excitability, and its contraction re-appears 

 when we open the circuit. If from the action of the inverse 

 current we return to that of the direct current, the contrac- 

 tions which are obtained during the short time that the nerve 

 preserves the excitability acquired by the passage of the 

 inverse current, will be more energetic, inasmuch as we 

 have seen that the direct discharge produces on a nerve, 

 endowed with a certain degree of excitability, a stronger 

 contraction than the inverse one. 



Effects on other Parts of the Nervous System. To com- 

 plete this lecture, it only remains for me to speak of the 

 effects which the electric current produces when applied to 

 different parts of the brain, to the nerves of sensation, to the 

 roots of the spinal nerves, and to the ganglionic nerves. I 

 regret that a subject so important has not hitherto been 

 properly investigated. We may say that every thing yet 

 remains to be done: the few words which I can say to you 

 on the subject will prove it. 



Effects on the Brain. I applied the conductors of a pile, 

 formed of several elements, to the cerebral hemispheres, 

 and to the cerebellum of the brains of a living animal ; and 



