Note 153 — PHARMACOLOGIA. ON THE OPERATIONS OF MEDICINAL BODIES, AND ON THE CLASSIFICATIONS FOUNDED ON THEM.

Few discoveries in physiology have thrown greater light upon this important subject than that of M. Majendie, published in his Journal De Physiologie Experimentale, (1er numero—Janvier, 1821) in a paper entitled, “Memoir sur le Méchanisme de L’Absorption.” The results contained in this essay are the more interesting to me, as they were read at the Academy of Sciences at Paris, some time after the publication of the Third Edition of my Pharmacologia, and it will be observed, in what a satisfactory manner they confirm the views which I offered at that time, respecting the influence of venesection in accelerating the absorption of Mercury. In the Fourth Edition (published in October, 1820, p. 115,) these views were farther extended, and as I could not have been influenced by the experiments of M. Majendie, which were not published until some time afterwards, it is very fair to conclude, that when two persons arrive at the same result by different trains of investigation, such a result must be correct. The conclusions established by the experimental inquiries of M. Majendie, with regard to absorption, appear to me to be so important, in reference to the object of the present work, that I shall pause, in this place, for the purpose of furnishing the reader with a short account of them. M. Majendie states, that while performing the experiment of injecting warm water into the veins of a living animal, he first conceived the idea of observing what effects would be produced upon the function of absorption by the artificial plethora, thus occasioned; having accordingly injected a quantity of water into the venous system of a middle-sized dog, he introduced a small portion of an active substance, whose effects were well known, into his side, when he was surprised to find that its usual operation was not manifested until after an interval much longer than usual; the same experiment was afterwards repeated upon another animal, and with similar results. In a third experiment, as much water (about two pounds) was injected, as the animal could sustain without destruction, in which case the poisonous substance produced no effect whatever, the powers of absorption appearing to be entirely suspended: and having waited during half an hour for the occurrence of those symptoms which, under ordinary circumstances, would have manifested themselves in two minutes, M. Majendie concluded that if vascular congestion be the cause of the suspension of absorption, the function ought to be restored by the removal of this artificial condition, an opinion which he proceeded to verify by experiment; the jugular vein of the animal, under trial, was accordingly opened, and the ingenious operator had the satisfaction to observe the effects of the poison gradually developing themselves in proportion as the blood flowed. M. Majendie next proceeded to confirm the truth of his position, by an experiment, the converse of those above related; an animal was bled, to the amount of about half a pound, and the poisonous substance applied to the pleura of the animal, as in the foregoing experiments, when it appeared that those effects which, under ordinary circumstances, were not evident until after a period of twelve minutes, manifested themselves after an interval of only thirty seconds. In order to shew that these results actually arose from vascular distention, and not from the artificial state of dilution in which the blood was placed, M. Majendie instituted the following experiment: a considerable quantity of blood was drawn from the vein of a dog, and replaced by a similar quantity of warm water, after which a measured quantity of Nux Vomica in solution was introduced into the side, when the poisonous effects were found to take place with the same rapidity as if the blood had not been mixed with water.