I first divided the sciatic nerves, in both legs of two frogs, and then tied the crural artery in one leg of each. Eight drops of the solution of opium were immediately afterwards injected upon their brains. But the event of this experiment was precisely the same with the majority of those before related. The contractions excited by the metals, in the legs whose arteries were tied, were uniformly more feeble, and of shorter duration, than those excited in the other legs: yet it is evident, that, in all these experiments, the very reverse of this ought to have taken place, had it been true, as M. Fontana has asserted, that opium has no effect upon any part of the body, except through the medium of the blood. The experiments however, which I am now to relate, may perhaps appear still more satisfactory. EXPERIMENT IX. Having laid equally bare both the sciatic nerves of a frog, at the upper part of its thighs, I passed a ligature round one of them, and drew it as tight as it was well possible, without dividing the nerve. I then removed a portion of its skull, and with a small brush, kept it constantly wet with laudanum during several hours. The frog soon became convulsed; and, during ten or twelve hours, continued in that state of exquisite sensibility, which opium never fails to produce in these animals. It may here be worth remarking, that, while they are in this state, the slightest touch of a feather, or even breathing upon them, excites instantaneous convulsions. The leg whose nerve was tied, remained paralytic during this time, but when it was laid upon zinc and excited with silver, it contracted as strongly as the other. After forty three hours, the contractions were very feeble in the leg whose nerve was not tied, but still vigorous in the other. After fifty three hours, no contractions could be excited in any part of the frog, except in the leg whose nerve was tied. In this they were sufficiently strong to move the foot, and continued so for more than an hour longer. EXPERIMENT X. One of the crural nerves of another frog having been tied in a similar manner, eight drops of the strong solution of opium were injected upon its brain. The animal instantly became motionless, but, in less than an hour afterwards, was considerably recovered. The contractions, excited by the metals, in the leg whose nerve was free, soon became more feeble than those excited in the leg, whose nerve had been tied. This disproportion, between them, continued increasing during ninety six hours, after the opium had been injected, when contractions could no longer be excited in the leg whose nerve remained free. In that, in which the nerve had been tied, they continued upwards of 4 hours afterwards. EXPERIMENT XI.