When we say that every fermentation has its own peculiar ferment, it must be understood that we are speaking of the fermentation considered as a whole, including all the accessory products. We do not mean to imply that the ferment in question is not capable of acting on some other fermentable substance and giving rise to fermentation of a very different kind. Moreover, it is quite erroneous to suppose that the presence of a single one of the products of a fermentation implies the co-existence of a particular ferment. If, for example, we find alcohol among the products of a fermentation, or even alcohol and carbonic acid gas together, this does not prove that the ferment must be an alcoholic ferment, belonging to alcoholic fermentations, in the strict sense of the term. Nor, again, does the mere presence of lactic acid necessarily imply the presence of lactic ferment. As a matter of fact, different fermentations may give rise to one or even several identical products. We could not say with certainty, from a purely chemical point of view, that we were dealing, for example, with an alcoholic fermentation, properly so called, and that the yeast of beer must be present in it, if we had not first determined the presence of all the numerous products of that particular fermentation, and that they were present in those proportions, characteristic of that fermentation under conditions similar to those under which the fermentation in question had occurred. In works on fermentation, the reader will often find those confusions against which we are now attempting to guard him. It is precisely in consequence of not having had their attention drawn to such observations that some have imagined that the fermentation in fruits, immersed in carbonic acid gas, is in contradiction to the assertion which we originally made in our Memoir on alcoholic fermentation, published in 1860, the exact words of which we may here repeat:—“The chemical phenomena of fermentation are related essentially to a vital activity, beginning and ending with the latter; we believe that alcoholic fermentation never occurs”—we were discussing the question of ordinary alcoholic fermentation produced by the yeast of beer—“without the simultaneous occurrence of organization, development, and multiplication of globules, or continued life, carried on by means of globules already formed. The general results of the present Memoir seem to us to be in direct opposition to the opinions of MM. Liebig and Berzelius.” These conclusions, we repeat, are as true now as they ever were, and are as applicable to the fermentation of fruits, of which nothing was known in 1860, as they are to the fermentation produced by means of yeast. Only, in the case of fruits, it is the cells of the parenchyma that function as ferment, _by a continuation of their vital activity in carbonic acid gas_, whilst in the other case the ferment consists of the cells of yeast.