APPENDIX. 



YEASTS AND MOULDS. 



IN works on bacteria, these true fungi, yeasts and moulds, are 

 usually considered. They are so closely related to bacteria, and 

 so often contaminate the culture media, and are so similar in 

 many respects, that a description is almost a necessity. 



But there are several thousand varieties, and we cannot 

 attempt to describe even all of the more important ones. It 

 will answer our purpose to detail a few of the more common 

 kinds, and give the principal features of the different orders. 



'Saccharomycetes or Yeasts increase through budding; the 

 spores are attached to the mother cell like a tuber on a potato. 



Yeasts are the cause of alcoholic fermentation in the saccha- 

 roses. A description of the most common ones will suffice. 



Saccharomyces Cerevisise. (Torula Cerevisice.) This is the 

 ordinary beer yeast. 



Form. Bound and oval cells ; a thin membrane inclosing a 

 granular mass, in which usually can be seen three or four irre- 

 gular-shaped spores. When these become full grown they pass 

 through the cell wall and form a daughter cell. Sometimes long 

 chains are produced by the attached daughter cells. 



Growth. They can be cultivated as bacteria in bouillon, but 

 they grow best in beer. 



There are several varieties of beer yeast, each one giving a 

 characteristic taste to the beer. Brewers, by paying special 

 attention to the nutrient media, cultivate yeasts which give to 

 their beers individual flavors. 



Mixed yeast gives rise to a poor quality of beer. 



Saccharomyces Kosaceus. S. Niger and S. Albicans, These 

 yeasts are found in the air ; and instead of producing alcoholic 



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