"If a number of flasks be charged with a clear nutrient solution, of a kind favourable to the growth of yeast and containing a fermentable sugar, and each of them be inoculated with a trace of a pure culture of different yeasts, such as are used in brewing, distillery work, vinification, &c., the cultures being then kept at room temperature for a couple of days, it will be found that cell reproduction and fermentation—manifested by the appearance of turbidity and gas bubbles—will occur in all. It will thereafter soon be possible to separate the flasks into two groups, according to the appearance presented. In the one group the yeast crop developed from the sowing will remain almost entirely within the liquid throughout the entire period of fermentation, and mostly at the bottom even from the start. Yeasts of this kind are termed bottom yeasts, and excite bottom-fermentation, the yeast crop being sedimental. In the other group the fermentation is very brisk and attended with the formation of large quantities of froth (head); and in the earlier stages a larger or smaller number of the new cells are raised to the surface by the ascending bubbles of gas, and remain there—provided the vessel be high enough to prevent frothing over—until fermentation is terminated and the froth breaks up, whereupon they sink down to the bottom of the liquid and increase the sedimental deposit. This kind of fermentation is termed top-fermentation, and the yeasts producing it are called top-fermentation yeasts. Typical examples of bottom-fermentation yeasts are afforded by the Munich lager-beer yeasts."