ON INDUCED CONTRACTIONS. ' 313 



the thin stratum that adheres to the muscle is sufficient to impede the circulation of 

 the proper current. 



It is therefore indubitable that if an induced contraction is propagated through a 

 stratum of the bad conductors mentioned, this induced contraction cannot possibly 

 be owing to a current generated in the contracting muscle^ and passing thence 

 into the nerve of the galvanoscopic frog. 



Nevertheless these experiments were so important for the theory of the phenome- 

 non of induced contraction, that I desired to try the effect of interposing between the 

 contracting muscle, and the nerve of the galvanoscopic frog, a still worse conducting 

 body than those mentioned. The body that has served me in these experiments has 

 been Venice turpentine nearly solid, and rendered more or less liquid by adding to it 

 a little volatile oil of turpentine. Having smeared over the thigh of a frog with this 

 mixture, and wetted the nerve of a galvanoscopic frog with it, I prepare the experi- 

 ment as usual, and the induced contraction continues. To prove the bad conducting 

 powers of the mixture made use of, I hasten to say, that if I apply one pole of the 

 pile with which I excite the contractions upon the stratum of the insulating mixture, 

 of course without penetrating to the muscle, and I touch with the other pole the 

 nerve of the galvanoscopic frog, the contractions are not excited in it. It is therefore 

 proved from this experiment that the induced contraction propagates itself through 

 a stratum of an insulating substance that prevents the propagation not only of the 

 muscular and proper currents, but also of that current which excites the inducing 

 contraction. 



If the insulating stratum exceeds certain limits of thickness, and the mixture has 

 not a convenient degree of fluidity, the induced contraction is wanting. It is how- 

 ever impossible to determine within what limits of thickness in the stratum and flu- 

 idity in the mixture this occurs ; it is sufficient for me to have established by expe- 

 riment that in some cases the induced contractions are obtained, while there is in- 

 terposed between the nerve and the muscle an insulating stratum which certainly 

 arrests the muscular and proper current, no less than an ordinary voltaic current. 



I shall say, finally, that I have never succeeded in obtaining the induced contrac- 

 tion when using a solid body interposed, however thin it might have been chosen, 

 and whatever might be its nature. For this purpose I used flakes of mica extremely 

 thin, flakes of sulphate of lime, gold leaf, paper smeared with glue, and leaves of 

 vegetables. The induced contraction is always wanting. It is however a very 

 curious, and I believe even important fact in its consequences, to obtain the induced 

 contraction through the skin of the muscles of the inducing frog. The experiment 

 never fails of success, whether the inducing contraction be excited by the electric 

 current, or by any stimulus applied to the lumbar plexuses of the inducing frog. 



Having thus described a long series of facts relative to the circumstances that in- 

 tervene in producing, in modifying, and in destroying the phenomenon of induced 

 contraction, it might be believed that with the aid of these I might ascend to the 

 physical theory of the phenomenon. 



