It is not, however, by one experiment, formidable as it must be allowed to be, that the innumerable hosts brought to the contest by M. Fontana ought to be combated. Besides, it might be objected even to this one, that the opium was introduced into veins, from which it must have been so much longer in passing to the arterial blood, than from the jugular vein, and consequently so much more diluted, and perhaps too altered in its nature before it got there, as might be sufficient to account for the difference of result in the two cases compared. The opportunity afforded by M. Galvani’s discovery, of putting the truth of the opinion held by M. Fontana more fully to the test, and the possibility which presented itself, that if any such principle, as he supposes in the blood, should really be found to exist there, it might prove to be identically the same with that discovered by M. Galvani, induced me to make the following experiments. EXPERIMENT I. Having selected two frogs as nearly as possible of the same size and vigour, I deprived one of its blood by opening, first, one of its crural veins, then, a crural artery, and last of all, the heart. To assure myself of the complete evacuation of its blood, I next injected water into its heart, and immediately afterwards forty drops of a strong aqueous solution of opium[14]. I then removed the sternum of the other frog, and having made an opening into the ventricle of its heart, injected into it likewise forty drops of the solution. Less blood was effused in doing this, than one would at first expect; for the ventricle contracts so strongly, immediately after the incision, as to prevent much blood from passing out, unless the incision be made, as it was in the other frog, purposely large. The moment, at which each injection was made, was accurately noted, and the time expended in evacuating the blood from the first frog, was allowed for. The frog, from which the blood had been withdrawn, ceased to contract, when irritated, very nearly an hour before the other, even calculating not from the time of injection, but from the moment I began to bleed it; nor could I by means of the metals excite contractions in it, for upwards of a day before they had ceased to be excitable in the other frog. EXPERIMENT II.