114 MORPHOLOGY AND LIFE-HISTORY OF YEASTS. 



developed top-fermentation yeasts are the species forming the 

 bulk of the pressed yeast prepared by the old (Viennese) pro- 

 cess. This pressed yeast consists exclusively of cells raised 

 from the mash by the head, and of the daughter-cells of same, since 

 it is impracticable to separate from the mash such cells as are 

 left therein. These two extreme types of yeast are connected 

 by a number of intei'mediate grades. The question of another, 

 and fundamental, difference between top- and bottom-feraienta- 

 tion yeasts will be discussed in the paragraphs relating to 

 melibiase. 



As soon as the piimary fermentation is manifestly at an end, 

 let us take a trace of the sedimental yeast from each of the 

 flasks, thin each sample down with a drop of water on a glass 



Fig. 127. — Saccharomyces cerevisiaj I. Hansen. 

 Cells from the sediment of a young culture in beer wort. Magn. 1000. {After Hansen.) 



slide, cover it with a cover glass, and examine it under a high 

 power (250-500) in the microscope. In many of the specimens 

 the cells will be found globular or oval in shape ; speaking 

 generally, most of the beer yeasts and brandy yeasts will pre- 

 sent this appearance. Kow because, since the time of Meyen, 

 the name Sacch'iromi/ces cerevisite has been usually applied 

 to beer yeast, it has gradually become the custom to say of 

 yeasts exhibiting approximately globular or oval cells of large 

 dimensions, that they are of the cerevisise type. Fig. 127 gives 

 an example of this class, namely a top-fermentation yeast isolated 

 by Hansen (XII.) from the stock yeast (of which it formed the 

 main constituent) of a top-fermentation brewery in Edinburgh 

 and called by him Saccli. eerevida' I. 



The sedimental yeast in other flasks will be found to differ 

 from the foregoing, inasmuch as it contains cells which, instead 

 of being globular or oval, are elliptical in shape. Yeasts of this 

 kind were invariably found in fermenting must by Reess (I.), 

 who called them Saccli. eJIiji-'^oiiJeii.^, which specific name gradually 

 became enlarged to a morphological designation, so that we 



