Chemical Agents on the Nervous System, 37 



the first circles have been divided, and the primary circle of 

 course interrupted. This fact may be illustrated by the fol- 

 lowing experiment. 



Ex. 15. If the frog be prepared as in fig. 5, in every 

 respect, muscular movements are observed in the lower ex- 

 tremity c, when the Voltaic arc is placed in contact with the 

 nerve and muscle ; but no movement is observed in b. If 

 now the portion of platinum placed in accurate contact with 

 the limbs b and c, be connected by means of a platinum wire, 

 movements are observed in both the limbs b and c. 



That these movements in 6, depend on a new circle pass- 

 ing from the zinc to the silver through the spinal marrow, 

 and the two limbs b and c, is proved by their persistence, 

 after the removal of the primary circle by dividing the nerve 

 at ^. 



It is not necessary that a perfect Voltaic arc be placed on 

 the nerve and muscles. It may be, as represented in fig. 6. 

 If a piece of zinc only be placed in contact with the nerve, as 

 in this figure, and connection be made by means of a plati- 

 num wire between the plate of zinc and the plate of platinum 

 6 or c, movements are observed in the limbs b and c, respec- 

 tively. The direction of the current is doubtless that pour- 

 trayed by the arrows. 



Sometimes, in addition to the movements of the limb 6, 

 when the zinc and this last are brought into connection by 

 means of the platinum wire, movements are also observed in 

 c, and vice versa. When c is brought into connection with 

 the zinc, there are movements in b ; these movements are 

 doubtless reflex. 



Movements are observed in both limbs, when the plate of 

 zinc and the small plate of platinum placed over the spinal 

 column at a, are brought into connection. No movements 

 are observed at the first, when b and c are united. 



It now remains for me to point out a new series of pheno- 

 mena. 



Ex. 16. In the first instance, no movements are ob- 

 served in 6, on making the connection between the portion of 

 the platinum at a and at 6, but when the plates of platinum 

 at a and b have been connected with the portion of zinc, by 



