214 Dynamic Theory. 



single species of alcoholic ferment, Succharomyces Cerevisiae, and along 

 with it microscopical quantities of lupuliii, crystals of calcium oxalate, 

 spores and mold. This deposit is of the consistence of a paste of 

 yellowish white or yellow ochre color. The cells are round or oval, 

 from 5- to of a millimetre { ^j to 3 of an inclrj in "their 



1OOO 100O V 100000 10OOOO / 



greatest diameter. They are formed of a thin and elastic membrane of 

 colorless cellulose and of a protoplasm, also colorless, sometimes homo- 

 geneous, sometimes composed of small granulations. 



FIG. 98. aSaccharomyces Cerevisise. Yeast of sedimentary beer. 

 b Same budding. X 400 



There are in the cells one or two vacuoles containing cellular juice. 

 The cells are separate, or united two by two. They multiply b}' budding. 

 A swelling appears usually on the side but sometimes on the end of a 

 parent cell. The swelling increases by the withdrawal of protoplasm 

 from the parent cell, the vacated space in the parent appearing as one or 

 more vacuoles. 



If the conditions are favorable the same cell is able to produce several 

 generations of cells, but by degrees it loses all its protoplasm, which at 

 last unites in granules swimming in the midst of superabundant cellular 

 juice. The cell then ceases to reproduce and even to live, the mem- 

 brane is ruptured and the granular contents are diffused in the liquid. 

 When the saccharomyces cerevisiae is not in contact with a fermentable 

 liquid it may remain for some time without becoming modified. In- 

 crease of temperature may increase the size of the cells from one-third 



FIG. 99. 



-Surface yeast of beer at rest. 

 d Same budding. 



to one-half. The surface variety buds much more quickly than the 

 sedimentary kind. In this variety also, the cells remain to some extent 



