29S 



Theory of Gal- 

 vani j that the 

 interior of the 

 muicle is 

 charged plus, 

 and the nerves 

 form a commu- 

 nication with the 

 outfide. 

 Gain's Letters 

 on Animal 

 Electricity, 



J793- 



Volta's Letters 

 to Cavallo, 

 1793' 



"No charge in 

 the animal. 



but electricity 

 from the con- 

 tact of different 

 metals applied to 

 the nerves. 



Thegalv. aftion 

 fuppofed to exift 

 in nerves only. 



HISTORY O! 1 GALVANISM. 



cither in the whole body or in particular parts of it, as long as 

 the animal pofieffes any remains of vitality. Galvani fuppofed 

 thefe phenomena to be analogous to the effects of the Leydcn 

 phial ; that there is an ejtcefs of electric fluid in the interior of 

 the mufcle or in the nerve, and a deficiency on the outfide, 

 or vv. The nerve he conceived to aft the part of the wire 

 in the Leyden phial. Soon after the publication of Galvani's 

 work, Valli's Letters on Animal Electricity appeared in the 

 Journal dePhvfique, vol. 41. & feq. 



In the Tranfactions of the Royal Society for 1796, Volta's 

 letter to Cavallo was publifhed, which befides giving an ac- 

 count of Galvani's difcovcries, contains many original experi- 

 ments and obfervations. The analogy of the Leyden phial he 

 (hows is without foundation, for he found that he could excite 

 fimilar contractions in the limbs, when the conducting circuit 

 only touched two parts of the nerve, two mufcles, or two 

 parts of the fame mufcle ; in order to accomplifh this, it is 

 however neeeflary to ufe two different metals. He fuppofes 

 that in thefe cafes the mufcular contractions are produced by a 

 fmall quantity of electricity which is excited by the action of 

 the metals upon each other ; this he conceives to depend upon 

 a general law of the electric fluid, and that its effects are vi- 

 fible in the experiments of Galvani only becaufe the prepared 

 animal is the moit delicate fpecies of electrometer. Volta 

 endeavours to prove by experiment, that the action is always 

 in the firft inftance upon the nerves, and that the mufcles are 

 only affected through their medium. He imagines that it is not 

 neeeflary that a communication fliould exift between the nerve* 

 and the mufcles according to the opinion of Galvani, he ima- 

 gines that the contractions will be produced in the limbs, if 

 the influence be only made to pafs from one part of a nerve 

 to another part of the fame. But we (hall find that in this idea 

 Volta is probably miftaken, as in his experiments the moifture 

 adhering to the nerve formed a communication between it and 

 the mufcle. He found that if different parts of a nerve, or 

 indeed if the body of the animal in general, be laid upon two 

 different metals, and thefe metals be made to communicate by 

 a conducing fubftance, mufcular contractions are produced. 

 Thefe experiments fucceed with more certainty when the fkin 

 is removed ; this precaution is more elpecially requifite if the 

 animal have a dry fkin, as is the cafe with birds and quadru- 

 peds. 



