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. 



A 



B 



6 

 / 



D 



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 vim. (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 



