Chemical Agents on the Nervous System. 257 



their surface, in contact with the glass, we instituted the 

 usual Voltaic current. 



In this experiment, again, no spasmodic movements were 

 observed, after passing the Voltaic cui'rent through the 

 nerves during five, ten, or twenty minutes, and even longer, 

 and breaking the circuit. 



We prepared a frog as in fig. 4, and having laid the moist 

 intestine over one of the nerves, we passed the Voltaic cur- 

 rent in the direction represented ; on breaking the current, 

 the spasmodic movements were observed in the limb the 

 nerve of which was exposed, and not in that of which the 

 nerve was kept moist by the intestine. The same thing was 

 observed on connecting the platinum plates or shillings ; yet 

 the nerves were not discharged ; for on removing the intes- 

 tine, and again uniting the platinum plates, the muscles of 

 both limbs were seen to contract with energy. 



It is obvious, therefore, that in experiments on electrogenic 

 conditions of the nervous system, we must carefully weigh 

 the influence of external moisture as well as of dryness ; the 

 former, as a conductor, discharges the electrogenic state, and 

 prevents the energetic spasmodic and tetanoid contractions 

 of the muscles, observed in cases in which the nerves are in- 

 sulated. This efifect of moisture enables me to explain some 

 other phenomena to be detailed hereafter, and especially the 

 absence of muscular contractions in breaking the Voltaic cir- 

 cuit, in that experiment which has been designated the " al- 

 ternative Voltaique." 



There is a third circumstance of great importance and in- 

 fluence. 



Having prepared a frog as in fig. 3, we subjected the lum- 

 bar nerves to the continuous action of the Voltaic current as 

 usual, with the sole exception of substituting platinum for 

 copper wires. The experiment utterly failed. No spasmo- 

 dic or tetanoid actions of the muscles were observed on break- 

 ing the Voltaic circuit. 



We observed that the copper wires were of greater diame- 

 ter than those of platinum. It occurred to me that the num- 

 ber of the points of contact between the wires and the nerves 

 might have its influence on this phenomenon, we therefore 



