PURIFICATION AND ISOLATION OF YEASTS 



157 



Lindner's Method for Securing Pure Cultures: Lindner has de- 

 vised many methods founded on the same principle but much simpler. 

 One of these known as the drop culture method consists in diluting 

 the yeast until each drop contains about a single cell. Beer wort may 

 be used as the diluent. By means of a pipette with a fine bore, 

 drops of this mixture are placed in the bottom of sterile Petri dishes. 

 Each cell will develop into a colony. From these 

 colonies pure cultures are obtained by means of 

 platinum wires. Transfers are made into nutrient 

 media in order to get the cells in greater quantity. 

 This procedure is not as sure as that of Hansen 

 but is short and serves in many investigations. 



Another method devised by Lindner is known 

 as the droplet culture procedure. This is much 

 like the above except that the solid medium is 

 placed on a cover slip which allows continued ob- 

 servations under the microscope. 



Determination of the Number of Cells in a Culture and Study of 

 the Multiplication Power of Yeasts: Very often it is desirable to 

 calculate the multiplication power of yeasts or the time required for 

 the cells to divide. One method of doing this is by means of the hemo- 

 cytometer. This apparatus, devised for counting the corpuscles in 

 the blood, consists of a glass slide upon which is fastened a cylindrical 



Fig. 67. Mode of 

 Operation for Drop- 

 let Cultures accord- 

 ing to the Method 

 of Lindner. 



Fig. 68. Hemocytometer. 



or square glass cover slip with a cylindrical hole in the center. In- 

 side this hole is fastened another glass disk which bears a ruled area. 

 When an accurately ground cover glass is placed over the larger cover 

 glass, this disk bearing the ruled portion should be exactly 1 mm. 

 below the bottom surface of it. The ruled area consists of squares 

 of different sizes, depending on the ruling which is used. The value 

 of these squares is usually marked on the end of the slide. While 

 there are many different rulings, the Thoma ruling is as satisfactory 

 as any. (Fig. 68.) 



After the yeast solution is carefully shaken to distribute the cells 

 evenly, a drop of it is placed on the disk of the hemocytometer and 



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