YEASTS. 



35 



tions, until finally a pure culture may be obtained. The principle of these methods is 

 of great use in practical fermentation, but is of little use in rigidly separating forms. 

 Methods of general application for the latter purpose must be such that a single 

 cell can be isolated in a sterile medium and a culture propagated from this single cell. 

 Separation by Dilution in Liquid Media. A mixed culture is diluted with sterilized 



Q 



J) 



FIG. 15. Wild and pseudo-yeasts. A, S. pombe. (After Lindner}; B, Torulce. 

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

 ulatus; E, Mycoderma vini. (After Bioletti.) 



water until each two drops contain one cell. A large number of flasks of a sterilized 

 nutrient medium is then inoculated from the dilution, one drop in each flask. If the 

 dilution has been properly made, about half of the flasks will remain sterile and half 

 will show growth. Many or most of the latter will contain pure cultures. 



Separation by Dilution in Solid Media. If we dip a sterilized platinum wire in a 



