The term
Induced
contractions was applied in England to a physiological fact discovered by myself, and described in the tenth chapter of my treatise on the Electro-physiological Phenomena of Animals. I shall henceforth adopt this denomination, since it has the advantage of expressing the phenomenon with brevity, and, to a certain degree, its nature. I will begin by explaining, in a few words, in what this fact consists, together with the principal researches which I made in the commencement for the purpose of discovering its laws. Having prepared a galvanoscopic frog, I laid its nerve upon one or both the thighs of a frog prepared in the ordinary manner; this done, on applying the poles of a pile upon the lumbar plexuses of the frog, at the same time that the muscles of the thighs were contracted, contractions were excited in the galvanoscopic leg, the nerve of which reposed upon the thigh of the other frog. I discovered the same fact, placing the nerve of the galvanoscopic frog upon a muscle of the thigh of a rabbit, and exciting the muscle to contraction by means of a current, which traverses its nerve. I have even seen contractions of the galvanoscopic frog occur without applying the electric current for the purpose of contracting the muscle which ought to induce the contractions, adopting for this purpose any other stimulus to the lumbar plexuses or to the spinal marrow. I finally tried these experiments, introducing between the nerve of the galvanoscopic frog and the inducing muscular surface very fine laminæ of different substances. A leaf of gold and a very fine non-conducting stratum of mica or of glazed paper being interposed prevented the phenomenon, that is to say, the induced contractions in the galvanoscopic frog failed to appear, whilst a stratum of fine paper soaked in water did not interrupt the induced contraction. From the whole of these facts I was led to conclude,—1st, that the contraction induced in the galvanoscopic frog could not be attributed to the effect of derived currents; 2nd, that it should rather be considered the effect of an electric discharge taking place during the contraction of a muscle. For the sake of supporting this explanation of the induced contractions by facts, I instituted a great number of experiments which are described in the tenth chapter above referred to. With this view I composed a pile of entire frogs, and closed the circuit with the two extremities of the galvanometer. Allowing the needle to become stationary, I touched specially the nerves of the frogs composing the pile with a solution of potassa, by which means contractions were excited in these frogs. Operating in this manner, I have often remarked the deflection of the needle to be increased by a few degrees, after which the needle retrograded. When the frogs were touched several times with the potassa, or were very much weakened, so that touching them again with the alkali no longer produced contractions, it has, in most cases, occurred that there was no sign of increased deflection in the needle of the galvanometer. Finally, bathing the nerves of frogs arranged in piles with acid or saline solutions, the deflection, far from increasing, rapidly diminished, at least in the beginning.
Electro-physiological researches.—Fourth memoir
