278 MANUAL OF BACTERIOLOGY. 



Yeasts and Moulds. — In the course of bacteriological work 

 one constantly encounters yeasts and moulds, which, although 

 not bacteria, must nevertheless be understood and recognized 

 to avoid error. Accidental contamination of tubes or plates 

 is likely to be the result of the growth of some of these forms. 

 The yeasts generally go by the name of saccharomyces, of which 

 there are several spices. The Saccharomyces cerevisia is the 



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m.- 



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Fig. 62.— Yeast cells stained with fuchsin. (X 1000.) 



ordinary yeast of alcoholic fermentation. Some of the yeasts 

 present colored growths— red, white and black. They con- 

 sist of large, oval cells, which readily stain with the aniline dyes. 

 They multiply by the protrusion of a little bud from the cell, 

 which develops into a new cell. In an actively germinating 

 growth of yeast these budding cells are readily distinguished 

 (Fig. 62). 



Among the moulds the varieties most commonly encountered 

 are the mucor, the penicillium, the aspergillus and the oidium. 



