On May 28th, 1875, we put a trace of pure, unicellular, “low” yeast, taken at the end of a fermentation, into a flask of wort. On May 29th, sixteen hours after impregnation, the temperature during the night having been 15° C. (59° F.), we made a sketch of the yeast before its development had become apparent to the naked eye. No perceptible development, that is to say, no visible deposit at the bottom of the liquid and formation of patches of froth on the surface, took place before May 30th. A mere glance at Fig. 42 will be sufficient to enable us to detect a considerable difference between it and Fig. 40, which represents the multiplication of the cells of “high” yeast. The cells of the “low” yeast are slightly smaller and rather more oval, as we have already had occasion to notice, and the budding processes are considerably less ramified, in consequence of which there is a comparative absence of globular clusters which are so striking a feature in the development of “high” yeast, when examined early enough. Moreover, if we cause our “low” yeast to age, by leaving it for a longer or shorter time in the beer which it has formed, or if we exhaust it in sweetened water by leaving it for whole months in a volume of sweetened water considerably larger than what it is capable of fermenting, and then proceed to revive it and cause it to propagate in an aerated saccharine wort capable of nourishing it, this yeast will resume its original aspect, as sketched and described. At most we shall observe certain minute differences in the size of the cells in successive growths. A very remarkable industrial characteristic of this yeast is the fact that it never rises to the surface, no matter at what temperature it may be working, whether between 6° C. and 8° C. or 15° C. and 20° C.;[102] in other words, it is not buoyed up by the carbonic acid gas when the fermentation is at its height. At the end of the fermentation, the surface of the liquid and the sides of the vessel above the level of the liquid are clean and not covered with the yeast, which remains altogether at the bottom of the fermented liquid. Moreover, the weight of new yeast which it yields is always less than that yielded by “high” yeast, for the same quantity of fermentable liquid, although greater than that which _saccharomyces pastorianus_ would give. Lastly, the beer possesses a flavour and delicacy which cause it to be held in higher esteem by consumers than beers produced by means of other ferments.[103] § IV.—On the Existence and Production of Other Species of Ferment. Our present knowledge of the alcoholic ferments embraces the following, without taking into account the ferment-form of _mucor_:— The ferment named after the author, which is found associated with the ferments of the grape and other domestic fruits, and with spontaneous ferments in general. The ferment of “high” beer. The ferment of “low” beer.