UPON INDUCED CONTRACTIONS. 
238 
What inferences may be drawn from these experiments to aid our decision as to 
whether the induced contraction admit of an explanation on the supposition of an 
electric discharge similar to that of the jar, and taking place during the contraction 
of the muscle ? 
Before examining this point, I will relate a few other experiments upon the induced 
contraction which throw some light upon the interpretation of this phenomenon. 
In a living dog, the spinal marrow (deprived of its membranes), the brain, the 
sciatic nerve, and the muscles of the thigh were all laid bare. Galvanoscopic frogs 
were placed in the usual manner upon these several parts, and at the same time the 
animal was irritated either by squeezing his paw, or by wounding the coverings of the 
spinal cord. The muscles of the thigh were thrown into violent contraction, and 
the animal howled from pain. In the meantime the galvanoscopic frogs placed upon 
the muscles in contraction alone exhibited the phenomenon of induced contraction. 
The same experiment was instituted upon a rabbit, and was followed with the same 
results. In like manner galvanoscopic frogs were arranged upon the abdominal 
viscera of a living rabbit while an electric current was passed along the pneumogas- 
tric nerves, or through the solar plexus. Never in the above experiments did the gal- 
vanoscopic frogs exhibit any indication of induced contractions. Now if it be borne 
in mind that in the experiments just related, while the animal shrieked with pain and 
was convulsed, there certainly was a current of that force, whatever may be its nature, 
which we term nervous, and yet no contraction in the galvanoscopic frogs placed on 
the nervous st ructures, we are forced to conclude that the phenomenon of induced con- 
traction belongs exclusively to the muscle in the state of contraction. 
With regard to the question whether the induced contractions admit of being ex- 
plained by the supposition of an electric discharge elicited in the act of the contrac- 
tion of the muscle, we are obliged to confess that the experiments recorded in the 
commencement of this memoir (and which are the only ones that in the present state 
of the science could have been instituted with a view to the decision of the question) 
are insufficient to afford a satisfactory solution. 
Admitting that an electric shock analogous to a very slight discharge of the jar did 
actually take place during the contraction of the muscle, we should have no other 
means of ascertaining its existence than that of the induced contractions, the origin 
of which we seek to discover. 
In effect, not one of our eiectroscopic instruments is capable of disclosing to us 
the existence of an electric discharge, such as that given by a very small jar previ- 
ously discharged three or four times successively with a metallic conductor. 
The galvanoscopic frog alone can indicate the existence of these discharges. 
Respecting the influence of the coating of turpentine upon the two phenomena 
under consideration, induced contractions, and discharge through a muscle which 
acts likewise upon the galvanoscopic frog, we have seen that no difference existed 
between the two cases. 
2 H 
MDCCCXLVII. 
