The direction of this influence, when suffered to pursue its natural course, appears to be the same with that of most other stimuli, i. e. from the place at which it first affects a nerve, onwards to the part, in which that nerve terminates. I have repeatedly caused electrical sparks to be passed into my own ulnar nerve at its passage over the inner condyle of the humerus, but both the sensations and the contractions produced by them have been entirely confined to the hand and fore arm. It appears too, both from the experiments of Dr Monro, and of Dr William Alexander of Halifax in Yorkshire, that when no communication is left between the trunk and posterior extremities of a frog, except by its sciatic nerves, a strong solution of opium, injected under the skin of its posterior extremities, deprives them both of their sensibility and of their contractile power; but that it does not in the least affect the trunk of the body. If, on the contrary, it be applied to the trunk, it exhausts both the trunk and the extremities. M. Galvani is said to have observed the effects of the influence, which he discovered, diffused over the whole body of a frog, when the metals were applied to a nerve merely laid bare, without being either divided or separated from surrounding parts. If we are allowed to infer this diffusion of the influence from the restlessness expressed by the animal, M. Galvani’s observation may be just. If from the contractions produced, I suspect it is by no means so; since, in every experiment which I have made upon the subject, the contractions have been confined to those parts to which the nerve touched by the metals was distributed. That this influence, however, may pass in a direction contrary to the course of nerves, is evident from some of the experiments which I have related relative to its effects upon the senses, but is still more clearly demonstrated by the following. If, after having divided at the pelvis a frog recently killed, the sciatic nerves be freed from cellular membrane up to their origin from the spine, and all the parts below this, except themselves, be cut away, the muscles on each side of the spine, for some little way up, may be brought into contraction by touching the nerves alone with the two metals in contact. This experiment has not always succeeded with me, and never unless the frog had been recently killed. So long as the hind legs remain undivided from the nerves, it never succeeded; the only contractions produced being in the legs. OF THE BLOOD VESSELS. We are told by Dr Valli, that no contractions are excited by arming the blood vessels; but as he has not told us whether his experiments were made upon them while the blood still continued to flow through them, or after they had been deprived of their blood, I determined to make the following experiment.