YEASTS 



77 



such as a slice of sterilized potato or a layer of nutrient gelatin in a petri dish we will 

 get a series of streak cultures. The first of these will develop a strong growth of mixed 

 forms. The last will show more and more isolated colonies until some of them will 

 show only a few, some of which may be pure cultures. 



B 



B 



FIG. 57. Wild and pseudo yeasts. A, S. pombe. (After Lindner). B, Torulce. 

 (After Pasteur.} C, Mucor, (i) spores; (2) germinating spores and mycelium. D, 

 S. apiculatus. E, Mycoderma vini. (After Bioletti.) 



The most useful method of separation and one which is applicable to most cases 

 is that of plate cultures, first used by Koch and improved by others. In this method a 

 drop of the mixed culture is thoroughly distributed in 10 to 20 c.c. of liquefied 

 nutrient gelatin or agar. A drop of this mixture is then diluted in the same way in 

 another portion of the same medium. This process is continued until the requisite 



