Fig. 51 represents the revival of this aërobian ferment. We recognize here the branched mode of budding and spherical contour characteristic of “high” yeast proper. Nor does the aërobian ferment of “low” yeast present any special peculiarities, in forms, dimensions, and mode of growth closely resembling the “low” yeast from which it is derived. At the commencement of its restoration, however, if this is performed in sweetened water, the cells in the groups are larger than those which are subsequently developed. [Illustration: Fig. 52.] Fig. 52 represents the aërobian ferment of yeast used in “low”-fermentation breweries, examined forty-eight hours after pitching. We find that groups resembling that at a are of very rare occurrence. They are to be seen only at the very beginning, generally only for the first few hours of the renewed activity. Very soon, however, they develop cells which are of the size of the oval cells budding at _b_. [Illustration: Fig. 53.] Fig. 53 represents the aërobian caseous yeast which forms rather rapidly, in thick, greasy-looking pellicles, on the surface of liquids which have been fermented by means of caseous ferment. The larger form of cells, _a_ and _b_, is not often met with. [Illustration: Fig. 54.] On May 27th, 1875, we sowed, in a flask of wort, a trace of a pellicle of this kind, which had formed on the surface of a flask in which fermentation had been set up by means of caseous yeast in May of the preceding year. On May 30th fermentation began to reveal its presence by a voluminous froth, and the newly-formed yeast had reached the bottom of the flask. A small quantity was taken out by a capillary glass tube, and a sketch of the ferment made; this is given in Fig. 54. Amongst the cells which occupy the field there are groups of some of larger size. These are not distinct forms mixed with the others, but simply another illustration of the fact that old cells in course of revival, especially when they have been exhausted in sweetened water, as we have just observed of the aërobian ferment of “low” yeast, commence with forms of larger diameter or more elongated than the ordinary forms peculiar to the ferment which at a later stage are developed from them. We have seen how marked and exaggerated this feature was in the case of _saccharomyces pastorianus_. Let us again call attention to the forms of aërobian ferment furnished by the yeast which we have already described under the name of _new “high” yeast_. Fig. 55 represents this aërobian ferment, as taken on November 27th, 1873, from a pellicle of rather greasy and moist appearance, on the surface of a flask of fermented beer-wort which had been impregnated on July 21st, 1872. It might readily be mistaken for ordinary “high” yeast, yet no two ferments can be more distinct. [Illustration: Fig. 55.] [Illustration: Fig. 56.]