220 ESSENTIALS OF BACTERIOLOGY 



very little resistant to heat. Monkeys inoculated through 

 the nose or directly into the brain. Immunity is produced 

 and an immune serum as preventive is obtained. The 

 stable-fly is supposed to act as a carrier of infection. 



CHAPTER XXX 

 YEASTS AND MOLDS 



IN works on bacteria these true fungi, yeasts and molds , 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 the more important ones. A 

 description of a few of the more common kinds must suffice. 



Blastomycetes (budding fungi) or yeasts increase 

 through budding; the spores are attached to the mother-cell 

 like a tuber on a potato (Fig. 108). 



Yeasts are "the cause of alcoholic fermentation in the sac- 

 charoses, and hence called saccharomycetes. 



Saccharomyces Cerevisiae (Torula Cerevisise). This 

 is the ordinary beer-yeast. 



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

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

 irregular-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 daugh- 

 ter-cells. 



Growth. They can be cultivated as bacteria are in bouil- 

 lon, but grow best in beer. 



Yeasts are very resistant: cultures have been obtained 

 from material twelve years old and dry as a bone. 



There are several varieties of beer-yeasts, each one giving a 



