Saccharomyces Cerevisiae. 



ORIGIN. Beer or bakers' yeast; at times in the air. 

 COLOR. White. 



FORM. Cells spherical or egg-shaped 8-10 p. broad. The 

 cells are colorless and when actively growing have a homo- 

 geneous protoplasm. Later, granules and vacuoles develop. 

 Owing to a gelatinous exudate it may form zoogleal masses. 

 The cells may be single or may have several buds; at times 

 long branching forms may be found, especially if the tem- 

 perature is about 30. 



MOTILITY. None. 



SPORULATION. Usually several spores form. Can be 

 double stained. Spores develop between 11 and 37. 



ANILIN DYES. Stain readily; so does Gram's method. 



GROWTH. Thick white growth, especially abundant on 

 glucose media and in wort. 



Gelatin plates. Small, opaque, white, circular colonies which are 

 very coarsely granular and slimy. 



Stab culture, The growth is confined to the upper portion of the 

 tube and spreads over the surface. It is thick and opaque white. 



Streak culture. On agar and on potato it forms a thick, somewhat 

 raised white growth. 



TEMPERATURE. As an "upper yeast" the most rapid 

 fermentation takes place between 14 and 18. 



BEHAVIOR TO GELATIN. Does not liquefy gelatin. 



AEROGENESIS. It gives rise to a ferment (invertin) which 

 changes cane-sugar into glucose. The latter is then 

 changed by another ferment, zymase, to carbonic acid and 

 alcohol (4-6 per cent.). It does not ferment lactose. 



PATHOGENESIS. It has no effect on animals. A large 

 amount may produce a catarrhal condition in the alimentary 



tract. 



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