CHAPTER VI 



METHODS OF CULTURE AND ISOLATION OF YEASTS. 

 PROCEDURES FOR THEIR STUDY 



A. Methods of Culture 



WITH the exception of a few pathogenic varieties, all of the 

 yeasts isolated up to the present time, grow well on artifi- 

 cial media. They may be cultivated according to the same 

 methods as bacteria. These procedures are sufficiently well known and 

 are outlined in detail in all books on bacteriology. It would be out 

 of place to mention them in a book of this nature. It will suffice to 

 mention here a few of the media and methods which are especially 

 adapted to the growth of yeasts. Like the 

 bacteria the yeast may be cultivated as well 

 on liquid as on solid media. As a rule, 

 unlike the bacteria, the yeasts desire a 

 slightly acid medium. The yeasts, although 

 facultative anaerobic, multiply only on media 

 which are well aerated. Since yeasts vegetate A 



more often at the bottom of cultures, it is Fi % 6 f Pasteur Flask; 



B, Chamberland Flask, 

 then necessary to place them in thin layers 



of medium in order to supply as much air as possible. On the contrary, 

 if a fermentation is desired, they should be placed under conditions 

 with a limited supply of oxygen and in a sugar medium contained 

 in deep flasks or tubes. 



For the culture of yeasts the same ordinary apparatus is utilized 

 as in the study of bacteria (Petri dishes, Erlenmeyer flasks, Roux 

 tubes, cover glasses, test tubes). For physiological investigations, 

 Pasteur, Chamberland, Freudenreich and Hansen flasks are service- 

 able. The Pasteur flask is shown in Fig. 62. It is provided with 

 two outlet tubes, one of which is bent and which contains a bit of cot- 

 ton to filter the air which is thus able to pass in. The other is a long 

 straight tube which enters the flask at the side. It is closed with 

 a piece of rubber tubing carrying a piece of glass rod in one end. 

 The other end of this tube is slipped over the tube from the flask. 

 Sterilization may be accomplished by putting in boiling water. Dur- 

 ing this sterilization, the rubber tube may be removed from the 



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