My purpose is not, by this brief notice, to give an exhaustive, or even a sufficient account, of the progress of fermentative action, by means of saprophytic organisms, on great masses of tissue; my observations have been incidental, but they lead me to the conclusion that the fermentative process is not only not carried through by what are called saprophytic bacteria, but that a _series_ of fermentative organisms arise, which succeed each other, the earlier ones preparing the pabulum or altering the surrounding medium, so as to render it highly favorable to a succeeding form. On the other hand, the succeeding form has a special adaptation for carrying on the fermentative destruction more efficiently from the period at which it arises, and thus ultimately of setting free the chemical elements locked up in dead organic compounds. That these later organisms are saprophytic, although not bacterial, there can be no doubt. A set of experiments, recorded by me in the proceedings of this society some years since, would go far to establish this (_Monthly Microscopical Journal_, 1876, p. 288). But it may be readily shown, by extremely simple experiments, that these forms will set up fermentative decomposition rapidly if introduced in either a desiccated or living condition, or in the spore state, into suitable but sterilized pabulum. Thus while we have specific ferments which bring about definite and specific results, and while even infusions of proteid substances may be exhaustively fermented by saprophytic bacteria, the most important of all ferments, that by which nature's dead organic masses are removed, is one which there is evidence to show is brought about by the successive vital activities of a series of adapted organisms, which are forever at work in every region of the earth. There is one other matter of some interest and moment on which I would say a few words. To thoroughly instructed biologists, such words will be quite needless; but, in a society of this kind, the possibilities that lie in the use of the instrument are associated with the contingency of large error, especially in the biology of the minuter forms of life, unless a well grounded biological knowledge form the basis of all specific inference, to say nothing of deduction. I am the more encouraged to speak of the difficulty to which I refer, because I have reason to know that it presents itself again and again in the provincial societies of the country, and is often adhered to with a tenacity worthy of a better cause. I refer to the danger that always exists, that young or occasional observers are exposed to, amid the complexities of minute animal and vegetable life, of concluding that they have come upon absolute evidences of the transformation of one minute form into another; that in fact they have demonstrated cases of heterogenesis.