One of the crural arteries of a frog having been included in a tight ligature, as near as possible to the body, I suffered four days to elapse, and then injected through a perforation in its skull, eight drops of the strong solution upon its brain, and in a direction towards its spinal marrow. This frog continued most violently convulsed for more than an hour, and, in two, was to all appearance dead. When laid upon zinc, and excited with silver, the contractions were not at first perceptibly stronger in one leg than in the other. After eight hours, however, they were evidently most strong in the leg whose artery remained free. After 21 hours, this difference became still more decided. At the end of 34 hours, scarcely any contractions could be excited in the leg whose artery had been tied; though they continued vigorous in the other; and, at the end of 46 hours, they had ceased altogether to be excitable, in the leg whose artery was tied. In the other, they continued during several hours afterwards. EXPERIMENT V. Having tied one of the crural arteries of another frog, I filled its stomach, immediately afterwards, with a saturated solution of opium in water. The difference between the strength, and the continuance of the contractions, excited by the metals, in the two legs of this frog, was not so great as in the former; yet still the difference was considerable in favour of that leg in which the artery remained free. EXPERIMENT VI. In two other frogs, in each of which a crural artery had been tied, and the solution of opium (without regard being paid to quantity), repeatedly injected underneath their skulls immediately after; the contractions appeared to be very little weaker in the legs, whose arteries were tied, than what they were in the legs in which they were not tied, and they continued excitable during an equal length of time in both. EXPERIMENT VII. Having tied the crural artery of another frog, I immediately filled both its stomach and abdomen with a strong solution of opium. In an hour after this, it was to appearance quite dead. At the end of eight hours, the contractions, excited by the metals, had become very feeble in the leg whose artery was tied, in comparison of what they were in the other leg; and, at the end of twelve hours, no contractions could be excited in any part of the frog, except in the leg whose artery remained free. In this they continued excitable about an hour longer. As it was possible, that the more speedy exhaustion of the legs, in which the arteries were tied, might have been owing in some measure to the pain, occasioned by that operation, I repeated the experiment with the following variation. EXPERIMENT VIII.