100 



A MANUAL OK BACTERIOLOGY 



Exercise 140. Preparation of Pure Cultures of Yeast from Single Cells 



1. Sterilize several .01 cc. -capillary pipettes by using 50 per 

 cent alcohol and warming them until the alcohol, is evaporated. 



2. Draw .01 cc. of a yeast culture from liquid wort and 

 examine under the microscope. Dilute the culture with sterile 

 wort until .01 cc. contains an average of one cell. (Instead of 

 the pipette a 2 mm.-platinum wire loop may be used.) 



3. Inoculate 1020 tubes of sterile wort with .01 cc. of solu- 

 tion containing one yeast cell. Incubate at 25 C. Where 

 growth appears, it is a culture developed from one cell. 



Exercise 141. Cultivation of Yeasts 



For much of the student's work yeast may be successfully cul- 

 tivated on various carbohydrate media, such as Naegeli's solution 

 (Exercise 58), wine must, apple must, and beer Avort. These 



media may be sterilized in 

 large test tubes or flasks, 

 with or without the addition 

 of agar or gelatin. In labora- 

 tories where cultures are to be 

 kept for some time, specially 

 constructed flasks are used 

 for yeast culture. These flasks 

 are provided with narrow 

 apertures, and consequently 

 evaporation of the culture 

 solution is diminished. The 

 Freudenreich type has a cap 

 which terminates in a narrow, 

 cotton-filled tube (Fig. 38). 



The Hansen flask has a cotton stopper in the wide opening, 

 over which a cap is fitted which terminates in a narrow tube 

 which also contains a tuft of cotton. It also has a side delivery 

 tube for transfer of the culture media to other flasks. This side 

 tube is closed with a short piece of rubber tubing and a glass 

 rod (Fig. 39). 



FIG. 38. Freud- 

 enreich flask 



FIG. 39. Hansen 



flask 



