158 



METHODS OF CULTURE AND ISOLATION 



the cover glass applied. After the cells have settled, they are counted 

 and the number calculated to the cubic centimeter or millimeter 



basis. By repeating this 

 operation for several times, 

 some idea may be secured 

 with regard to the progress 

 of yeast development. 



SI at or l used the warm 

 stage to determine whether 

 there was a lag phase in the 

 development of yeast. 

 (Fig. 68-A.) By means of 

 this method he was able to 

 follow under the microscope 

 the development of the yeast. 

 He- pictures graphically the 



Fig. 68-A. Warm Stage for Observing the budding of the yeasts 

 Development of Yeasts. ,_. n _ _ N . . 



(Fig. 68-B) and found that 



there was a short lag-phase in the yeast development which lasted for 

 two hours, after which the cells reproduced at the usual rate. For spores, 

 the lag phase was longer. 



^\ 16 



\ s 10 



Methods of Studying the 

 Yeasts 



Observation of Develop- 

 ment in Moist Chambers: The o 12 

 observation of yeasts presents 

 no serious difficulties and the 

 details will not be outlined here. Fig. 68-B. Slater's Method for Observing 



The simplest method is the one east Devel P ment on the Warm 

 used by early workers, Ehrenberg, Mitscherlich, Kiitzing, Schulze, and 

 Brefeld; it consists in diluting the culture of yeast to such a point 

 that each drop contains only a few cells. A drop of this culture is 

 put on a cover slip which is placed over a moist chamber and 

 incubated at 25 C. The various changes which take place in this 

 drop may be followed on the microscope. Observations may be ex- 

 tended, if desired, for a long time. 



The use of the ordinary moist chamber, and especially that of 

 Bottcher, is more convenient. It makes it possible to observe a single 

 cell or a small number of cells for a period of 8 days without danger 



1 Slator, A. Some observations on yeast growth. Biochem. Jour. 12, No. 3, 

 248-258, 1918. 



