Let us not, then, be surprised at the seemingly discordant results arrived at, and at the contradictory observations which have been made in the best faith possible, and with every regard to truth in science. The circumstances which seemed to be identical are merely analogous, but in point of fact are essentially distinct, as proved by the results. Changes inappreciable by human sense and as yet by philosophical instruments, may and no doubt do effect results, to man seemingly contradictory, simply because he comprehends them not. As chemical science makes progress, these differences are being reconciled and understood. Thus, as mere temperature exercises a truly remarkable influence over the nature of the products of fermentation, may it not be the efficient cause of the difference we observe between the malaria of the delta of the Mississippi and that floating near the muddy banks of the Scheldt? The juice of carrots, beet-root, or onions, which is rich in sugar, when allowed to ferment at ordinary temperature yields the same products as grape-sugar, but at a higher temperature the whole decomposition is changed--there is a much less evolution of gas, and no alcohol is formed. In the fermented liquor there is no longer any sugar, and thus may it be in the great laboratory of nature; the product of the fermentation will assume in one locality a character it does not possess in another. The elements are the same; there is merely a change in temperature. Are there facts to prove that certain states of transformation or putrefaction in a substance, are likewise propagated to parts or constituents of the living animal body? Such facts exist. On no other principle but that of assimilation can we explain the phenomena of poisoning by the puncture of the living hand in dissecting-rooms, the instrument being impregnated with a fermentescible and putrefactive substance, there undergoing a decomposition. Similar, unquestionably, must be the action of animal poisons, such as that of poisonous substances, whether animal or vegetable, of the poisons giving rise to zymotic diseases, &c.; and such may be the origin of the fevers caused by the unknown principle which must still be connected with the decomposition of organic bodies most frequently found in marshy countries. But before entering more fully on this important matter, I shall first weigh the evidence for and against a theory long fashionable, and which may even now have its supporters--namely, whether fermentation or the revolution of higher or more complex organic vegetable into less complex compounds, be the effect of the vital manifestations of vegetable matters, and whether putrefaction or the same change in animal substances be determined by the development or the presence of animal beings. They who maintain this theory, assume as a natural consequence of the views that the origin of miasmatic or contagious diseases, in so far as they may be referred to the presence