LECT. XIV. XV. INDUCED CONTRACTIONS. 285 



cause of this phenomenon really resides in this shock, how 

 can we explain the cessation of the induced contraction, 

 occasioned by the interposition of a very thin leaf of gold, 

 or mica, between the nerve and the muscle? I have very 

 frequently tried the effect of applying the nerve of the gal- 

 vanoscopic frog upon plates of metal or glass, upon tense 

 membranes, and upon vibrating catgut strings, and have 

 never seen contractions manifested in the galvanoscopic 

 frog. It is not then the shock of the contracting muscle 

 against the nerve of the galvanoscopic frog which is the 

 cause of induced contraction. 



3dly, In some extremely rare cases contraction in the 

 galvanoscopic frog is produced when we extend its nerve 

 upon the thigh of the second frog, where both are perfectly 

 insulated. But whenever this anomaly presents itself we 

 never fail to discover the cause. It sometimes depends on 

 some portion of the internal part of the muscle being ex- 

 posed; sometimes on some portion of the muscle being left 

 attached to the nerve of the galvanoscopic frog, and touching 

 the nerve when we place it on the thigh. It appears to me, 

 also, that these contractions are sometimes manifested when 

 we touch the tendinous extremities, and the surface of the 

 muscles of the thigh, with two points of the nerve of the 

 galvanoscopic frog. I begin by telling you, that induced 

 contraction is invariably obtained in all eases where, from 

 all the precautions that have been taken, there exists no 

 circumstances capable of exciting contraction in the gal- 

 vanoscopic frog. We also know, that by dividing with 

 scissors the muscular surface of the thighs, and rendering 

 it by this means perfectly smooth, the contraction by in- 

 duction takes place, when we apply the nerve of the gal- 

 vanoscopic frog upon the fresh muscular surface. It is also 

 produced through the skin of the frog, and even by placing 

 layers of insulating liquids between the muscle and the 



