In comparing these facts with those which we have pointed out in connection with the cultivation of _penicillium_ and _aspergillus_, we are compelled to admit that the production of alcohol and carbonic acid gas from sugar—in one word, alcoholic fermentation—is a chemical action, connected with the vegetable life of cells which may differ greatly in their nature, and that it takes place at the moment when these cells, ceasing to have the power of freely consuming the materials of their nutrition by respiratory processes—that is, by the absorption of free oxygen—continue to live by utilizing oxygenated matters which, like sugar or such unstable substances, produce heat by their decomposition. The character of ferment thus presents itself to us, not as being peculiar to any particular being or to any particular organ, but as a general property of the living cell. This character is always ready to manifest itself, and, in reality, does manifest itself as soon as life ceases to perform its functions under the influence of free oxygen, or without a quantity of that gas sufficient for all the acts of nutrition. Thus we should see it appear and disappear concomitantly with that mode of life; feeble and fugacious in its action when the conditions of this vitality are of a similarly restricted character; intense, on the other hand, and of long duration and productive of large quantities of carbonic acid gas and alcohol, when the conditions are such that the plant or cell can multiply with facility in this novel manner. To this we may attribute all possible degrees of activity in fermentation, as well as the existence of ferments of every variety of form and of very different species. It may readily be imagined that sugar may undergo decomposition in a quite different manner from that of which we have spoken, that instead of alcohol, carbonic acid gas, glycerine, and similar substances, it may yield lactic, butyric, acetic, and other acids. It would be only one definite class of cellular organisms, the members of which resembled each other more or less, that decomposed sugar into alcohol and carbonic acid; others, specifically different, would act in a different manner. In short, we may say that the number of these living organisms is a measure of the number of different ferments.