A 300 cc. (10-oz.) flask, containing 100 cc. of must, after the air in it had been expelled by boiling, was open and immediately re-closed on August 15th, 1873. A fungoid growth--a unique one, of greenish-grey colour--developed from spontaneous impregnation, and decolourized the liquid, which originally was of a yellowish- brown. Some large crystals, sparkling like diamonds, of neutral tartrate of lime, were precipitated, about a year afterwards, long after the death of the plant, we examined this liquid. It contained 0.3 gramme (4.6 grains) of alcohol, and 0.053 gramme (0.8 grain) of vegetable matter, dried at 100 degrees C. (212 degrees F.). We ascertained that the spores of the fungus were dead at the moment when the flask was opened. When sown, they did not develop in the least degree.] The conclusions to be drawn from the whole of the preceding facts can scarcely admit of doubt. As for ourselves, we have no hesitation in finding them the foundation of the true theory of fermentation. In the experiments which we have described, fermentation by yeast, that is to say, by the type of ferments properly so called, is presented to us, in a word, as the direct consequence of the processes of nutrition, assimilation and life, when these are carried on without the agency of free oxygen. The heat required in the accomplishment of that work must necessarily have been borrowed from the decomposition of the fermentable matter, that is from the saccharine substance which, like other unstable substances, liberates heat in undergoing decomposition. Fermentation by means of yeast appears, therefore, to be essentially connected with the property possessed by this minute cellular plant of performing its respiratory functions, somehow or other, with oxygen existing combined in sugar. Its fermentative power--which power must not be confounded with the fermentative activity or the intensity of decomposition in a given time--varies considerably between two limits, fixed by the greatest and least possible access to free oxygen which the plant has in the process of nutrition. If we supply it with a sufficient quantity of free oxygen for the necessities of its life, nutrition, and respiratory combustions, in other words, if we cause it to live after the manner of a mould, properly so called, it ceases to be a ferment, that is, the ratio between the weight of the plant developed and that of the sugar decomposed, which forms its principal food, is similar in amount to that in the case of fungi. [Footnote: We find in M. Raulin's note that "the minimum ratio between the weight of sugar and the weight of organized matter, that is, the weight of fungoid growth which it helps to form, may be expressed as 10/3.2=3.1." JULES RAULIN, Etudes chimiques sur la vegetation. Recherches sur le developpement d'une mucedinee dans un milieu artificiel, p. 192, Paris, 1870. We have seen in the case of yeast that this ratio