In the course of this work we shall combat, by means of experimental proofs which appear to us irrefragable, the opinions which many writers entertain on the subject of certain transformations of organisms—that of _penicillium glaucum_ into ferment, or _mycoderma_; of _bacteria_ into lactic ferment; of ferment into _vibrios_; of _mycoderma aceti_ into ferment, and so on. Nevertheless, we shall pronounce no _a priori_ opinion on the question whether the inferior organisms, which will be the subject of this chapter, and which include yeast and the ferments properly so called, are perfect beings in their habitual form, or whether they are susceptible of polymorphism. It is with this reservation that we employ the word _autonomy_. If we claim polymorphism for any species, we shall not do so without furnishing proofs. Some organs detached from higher organisms, and some beings in a certain phase of their existence, may reproduce themselves under a special form, with special properties, when brought into media and under conditions that are unfit for the production of the plant or animal under its other shape or ordinary mode of reproduction. Modern Science affords many examples of this, and certain alcoholic ferments present us with analogous facts; but to wish to stretch these facts beyond their due significance, and to admit a polymorphism that cannot be proved, in consequence of a belief that it is possible, or on the faith of confused observations, is to indulge in gratuitous assertion from a mere spirit of system. Footnote 50: See, on this subject, the author’s _Études sur le Vinaigre_, Paris, 1868, p. 76, note; and especially _Études sur le Vin_, 2nd Edition, 1873, p. 19. Footnote 51: