ISOLATION OF SACCH. CEREVISLE 115 



A. Isolation of Saccharomyces Cerevisiae 



Method. 1. Sterilize the potato knife in the flame of 

 the Bunsen burner. 



2. As soon as cool, cut a piece off the yeast cake. 



3. Make three dilution plates in dextrose agar imme- 

 diately from this freshly cut surface. Use the straight 

 needle and transfer only a very minute quantity of the 

 yeast. Distribute well with the platinum needle. Use 

 the straight needle for making dilutions in all cases. 



4. When the colony develops (three to six days) examine 

 under objective No. 3, ocular No. 1, inverting the plate 

 for this purpose. 



The individual cells of most yeast colonies may be 

 seen under objective No. 3, while individual bacteria can 

 seldom be distinguished in the colony at this low magni- 

 fication. 



5. When you have located a yeast colony make a hang- 

 ing drop from it in water and determine the shape of the 

 individual yeast cells. 



6. If they have the shape and size of Sacch. cerevisice 

 (see Marshall, p. 32), inoculate a tube of wort from this 

 colony. 



7. Study this yeast according to directions in Exercise 

 42. 



B. Study of Flora of Compressed Yeast Cake 



Method. 1. After preparing plates, place the yeast 

 cake in a sterile Esmarch dish. 



2. Add 1 c.c. of boiled water, using a sterile pipette. 



3. From the freshly cut surface, prepare a hanging drop 

 of the yeast in water, adding a loopful of iodin solution 

 to it. Yeast cells will be unstained, while starch grains 

 become blue. 



4. Repeat every seven days. 



