Immediately after having divided the sciatic nerve, in one thigh only, of three other frogs, I injected as much of the strong solution of opium underneath their skulls, as could possibly be retained. The legs, in which the nerves had been divided, continued contractile several hours after the others had ceased to be so. Hence, then, we see no reason for suspecting that the more speedy cessation of contractions in those legs, in which the crural arteries were tied, than in those on which no operation was performed, was owing to the pain occasioned by such operation, since even the more painful operations of tying or dividing the sciatic nerves, were attended with no such effect. Upon the whole, therefore, it appears, that the conclusion which M. Fontana draws from his numerous experiments with opium, ‘That the circulation of the blood and humours in the animal machine, is the vehicle for opium, and that, without this circulation, it would have no action on the living body,’ is the very reverse of that which I am warranted to draw from the experiments I have just related; since the parts, most affected by the action of opium, were not those in which the circulation remained most entire, but those in which it had been almost altogether interrupted; and since in two parts where the circulation remained equal, and entire, the action of opium was rendered unequal, by interrupting the communication of one of them, by means of nerves, with the parts to which the opium was applied. The existence, consequently, of any such principle in the blood, as that supposed by M. Fontana to exist there, is rendered far too problematical, even to allow me to expect that it can ever be proved: far less that it may turn out to be the same with that discovered by M. Galvani, or with that, whatever it may be, upon which the phenomena of nerves and of muscles may depend. ----- Footnote 13: Essays Physical and Literary. Footnote 14: This solution, which is the same that I employed in all my subsequent experiments, was of the same strength with that used by Dr Alexander in the greater number of his, viz. an ounce of crude opium mixed in a mortar with two ounces and a half of water, and filtered through paper, after having remained twelve hours, in a close corked bottle, near a chamber fire. ------------------------------------------------------------------------ APPENDIX. I was unwilling to interrupt the narration of the preceding experiments, by the mention of the following facts, which they afforded me an opportunity of observing, as they were not immediately connected with the objects on account of which the experiments were instituted; and I have yet some few to relate, which, from the haste with which these sheets were prepared for the press, I had omitted to insert in their proper places.