The influence discovered by Galvani appeared to me an admirable test, by which something decisive might be ascertained relative to these important points in the physiology of animals, and as such I have employed it in the following experiments. Considering, therefore, the brain on the one hand, and the sanguiferous system on the other, as the possible sources from which nerves and muscles might derive their power, I began by comparing the effects which result from interrupting their communication, first with the brain, and then with the arteries. This mode of procedure seemed to afford the best prospect of information with respect to every object which I had in view, but particularly with regard to the relations which this influence may bear to the several parts examined. Before relating the experiments, I must observe that the comparison was instituted between the effects of only partially interrupted communication; since it must be obvious that a complete interruption, either of nervous or of arterious communication between any part of an animal, and the rest of its body, could not have been effected without so far injuring the animal, as to render the result fallacious. _Experiments in which the Sciatic Nerves of Frogs were divided._ EXPERIMENT I. I divided the sciatic nerve, on one side only, in four large frogs. The division was made at the very top of their thighs, and before the nerve had given off the first large branch to the muscles of the thigh. This nerve lies immediately underneath the large crural artery, to which it is closely attached by a sheath of fine but very strong cellular membrane. A small nerve, which supplies some of the muscles on the under side of the thigh, was suffered to remain undivided. The legs, whose nerves had been divided, became completely paralytic below the knee, and very nearly so above it. These legs too, immediately after the division of their nerves, contracted vigorously when laid upon zinc, and excited by passing a rod of silver in contact with the under part of the knee till it touched the zinc; but the other legs which were suffered to remain in their natural state, in order that the contractility of one leg might all along be compared with that of the other, did not contract when the metals were similarly applied to them. These frogs were all killed by cutting off their heads; the first, at the end of two days after dividing the nerve; the second, at the end of five days; the third, at the end of seven; and the fourth, at the end of nine. Their legs were carefully examined, in the manner I have described, four or five times every day after their heads had been taken off, so long as any contractions could be excited; but I could not perceive, in any one of these instances, that the contractile power continued either longer or more vigorous in the legs, in which the nerves were not divided than it did in those in which they were.