HISTORY OF GALVANISM. 11 



electricity to all parts of the body. Volta per- 

 formed many experiments, in order to discover 

 what circumstances are favourable to the excita- 

 tion of the contractions, and what parts of the 

 body are the most easily called into action. His 

 observations agree, in almost all respects, with 

 Fowler's, although it is certain that their experi- 

 ments must have been made without concert or 

 communication. He found that snails and worms 

 could not be made to contract ; but that many of 

 the insects, as butterflies and beetles, were subject 

 to the influence of the metals. It appeared from 

 his numerous trials, that those animals alone were 

 sensible to galvanism who are furnished with 

 distinct limbs, having flexor and extensor mus- 

 cles. In the animals of this description, he sup- 

 posed that it was the voluntary muscles alone 

 which are capable of being made to contract. Al- 

 though the heart is a muscle which is easily 

 thrown into powerful action, by chemical or me- 

 chanical stimuli, yet he could never produce any 

 effect upon it by the action of the two metals. 

 Volta made some of the same observations upon 

 the effect of the two metals on the organs of sense 

 as have been mentioned in the account of Fow- 

 ler's Essay. 



In these letters Volta lays down the basis of the Voita's 



. . . theory. 



theory of galvanism, which, with certain modifi- 

 cations, he has since so zealously defended, and 

 which may be regarded as the one that has been 

 most generally received. He argues against the 



6 



