776 YEAST lution of carbonic acid gas. This want of buoyant gas is the cause of its settling to the bottom, and there, in consequence of less ex- posure to the air, it becomes less active ; but Flo. 1. Saccharomyces ce- revisiB Yeast of sedi- mentary beer, budding, magnified 400 diameters. Fio. 2. Saccharomvces ce- revlsiae Yeast of" surface beer, budding, magnified 400 diameters. its activity can be readily restored by raising the temperature of the fermenting mass, in which case, after a few fermentations, the sedi- mentary is converted into surface yeast. The cells of saccharomyces cerevisia) are round or oval and from -00031 to -00035 of an inch in diameter. (See figs. 1 and 2.) The cell wall is an elastic membrane of colorless cellulose, with colorless protoplasm, which often contains small granules, and one or two vacuoles con- taining cellular juice. When the cells are not undergoing development they are usually sepa- rate ; but when the yeast is forming, its meth- od of growth causes the cells to be joined to one another in pairs, groups, or chains, the lat- ter being more particularly the case in the rapid development of surface yeast. During fermen- tation, or the development of yeast, there is an elevation of temperature, probably due to the combustion of oxygen, which may be ob- tained from the air or from the decomposition of sugar in the fermentable liquid. In fact the respiration or consumption of oxygen by the yeast cells bears some comparison to the respiration of animal pulmonary tissue. The multiplication of the cells of Saccharomyces when in contact with an appropriate ferment- able liquid is by budding, but under other cir- cumstances, as has been shown by Reess and Fio. 8. Saccharomyces el- lipsoideus, in process of budding, magnified 600 di- ameters. Fio. 4. Saccharomyces ex- iguus, magnified 850 diam- eters. others, it may multiply by means of spores. (See Schutzenberger "On Fermentation," New York, 1876, pp. 49, 50.) S. eWpsoidem is Pasteur's ordinary alcoholic ferment of wine. The adult cells have an ellipsoidal form, being about -00024 in. in length by -000176 in. in breadth. (See fig. 3.) The multiplica- tion by budding and by spores does not differ from that of 8, cerevisice. S. exiguus, fig. 4, according to Reess, has cells of only -000098 in. in breadth by -000118 in. in length, and multiplies like the other varieties. S. con- glomeratus, fig. 5, is rare, and is found mostly in the must of wine toward the end of fer- mentation. It has spheroidal cells -000236 in. in diameter, conglomerated together; the cells, springing from buds, do not become detached from the parent cell until they have at- tained the same size. S. apiculatus, fig. 6, Fio. 5. Saccharomyces con - fflomeratus, magnified 600 diameters. Fio. 6. Saccharomyces api- culatus, magnified 600 di- ameters. is the most abundant alcoholic ferment, and is found on tho surface of all kinds of fruit, especially on berries and stone fruits. It has been found in certain kinds of beer, as that of Belgium, which undergoes spontaneous fer- mentation, yeast not being added to the wort. According to Engel, this species does not belong to the genus saccharomyce, and he calls it carpozyma apiculata. The greater diameter of the cells is about -000236 in. S. Pasto- rianus, fig. 7, is a species which appears in the Fio. 7. Saccharomyces Pas- Fio. 8. Saccharomyces Ree- torianus. alcoholic ferment sit, ferment of red wine, of wine, magnified 400 diam- magnified 850 diameters, eters. after fermentation of wines, especially of sweet wines, and those of other fruits than the grape. The cells are oval, pyriform, or club- shaped, and vary in dimensions from -000236 to -00078 of an inch. & Reesii, fig. 8, accom- panies S. ellipsoideus in the must of red wines. It has elongated cylindrical cells. S. myco- derma (mycoderma vini) is shown in fig. 9. The mucor mucedo and M. racemosus, fig. 10, have the property, when placed in a solution of sugar and protected from access of oxygen, of transforming or dividing their mycelium into joints having the form of balls, which latter multiply by budding. "This fact," Schiit-
