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LESSON VII 



SACCHAROMYCES 



Every one is familiar with the appearance of the ordinary 

 brewer's yeast — the light-brown, muddy, frothing substance 

 which is formed on the surface of the fermenting vats in 

 breweries and is used in the manufacture of bread to make 

 the dough "rise." 



Examined under the microscope yeast is seen to consist 

 of a fluid in which are suspended immense numbers of 

 minute particles, the presence of which produces the mud- 

 diness of the yeast. Each of these bodies is a unicellular 

 organism, the yeast-plant^ or, in botanical language, Sat- 

 charomyces cerevisicz. 



Saccharomyces consists of a globular or ellipsoidal mass 

 of protoplasm (Fig. 12), about y^^ mm. in diameter, and 

 surrounded with a delicate cell-wall of cellulose (c, cmi). 

 In the protoplasm are one or more non-contractile vacuoles 

 (^ac) — mere spaces filled with fluid and varying in number 

 and size according to the state of nutrition of the cell. 

 Granules also occur in the protoplasm, some of them being 

 of a proteid material, others fat globules. Under ordinary 

 circumstances no nucleus is to be seen : but by the em- 

 ployment of a special mode of staining, a small rounded 



