114 GENERAL MICROBIOLOGY 



YEASTS 



The so-called yeasts are divided into true yeasts " Sac- 

 charomycetes " (wild and cultivated), and pseudo-yeasts 

 or false yeasts, " Torulce " and " Mycodermata." 



By true yeasts are meant those which usually produce 

 alcoholic fermentation (Sacch. membrancefaciens is an ex- 

 ception), and which are able to form endospores. 



Pseudo-yeasts do not form endospores and produce 

 little or no alcoholic fermentation. 



Sacch. cerevisice, the yeast used in the manufacture of 

 beers and in bread-making, is a good example of the culti- 

 vated yeast. 



Sacch. apiculatus and Sacch. ellipsoideus are examples 

 of wild yeasts which are necessary in the making of wines. 

 (These yeasts are cultivated and pure cultures used to some 

 extent.) 



Torula rosea is an example of the pseudo-yeast. These 

 look like true yeasts, reproduce by budding, but seldom 

 produce alcoholic fermentation. 



REFERENCES 



MARSHALL: Microbiology, pp. 28-36, 420-423, 440, 460. 

 KLOCKER: Fermentation Studies, pp. 205, 249, 289, 296. 



EXERCISE 40. TO ISOLATE A PURE CULTURE OF SAC- 

 CHAROMYCES CEREVISICE AND TO STUDY THE 

 FLORA OF A COMPRESSED YEAST CAKE 



Apparatus. Cover-glasses; concave slide; sterile 

 Esmarch dishes; potato knife; platinum needles; Bunsen 

 burner; sterile pipette; three tubes of sterile dextrose 

 agar; iodin solution; methylen blue (0.0001% aqueous 

 solution) . 



Culture. Fresh compressed yeast cake. 



