LECT. XIV. XV. INDUCED CONTRACTIONS. 283 



layer ought to possess to yield this result. It is sufficient 

 for me to have fully shown that, in some circumstances, we 

 obtained induced contraction when we have interposed, 

 between the muscle and the nerve, an insulating layer, 

 which certainly impedes the propagation of the proper, or 

 muscular currents, as well as an ordinary voltaic current. 



Finally, I may state that I never succeeded in obtaining 

 induced contraction, by interposing between the nerve and 

 the muscle a solid body, whatever its nature and however 

 slight its thickness might be. I have employed for this 

 purpose very thin layers of mica, sulphate of lime, of gold, 

 sized paper, and the leaves of plants, but the phenomenon 

 was not produced with any of them. A very curious fact, 

 and which, from its consequences, I believe to be important, 

 is that of the existence of the induced contraction through 

 the skin of the inducing muscles of the frog. This experi- 

 ment constantly succeeds, whether the inducing contraction 

 be excited by means of the electric current, or by any 

 other stimulant applied to the lumbar plexus of the inducing 

 frog. 



Hypotheses of Induced Contractions. After having thus 

 enumerated a long series of experiments relative to the cir- 

 cumstances which intervene in producing, modifying, or 

 destroying, the phenomenon of induced contraction, one 

 would hope that, with such a collection of facts, it would 

 be easy to give the physical theory of the phenomenon. 

 Unfortunately, I believe that such is not possible, and this 

 doubt obliges me to discuss minutely the different hypo- 

 theses which can be formed to explain induced contrac- 

 tions. 



1st, It is sufficient to have once seen this phenomenon 

 produced by provoking the inducing contractions with any 

 mechanical stimulant, to be convinced that the electric 

 current, employed to excite the contraction, is not propa- 



