150 METHODS OF CULTURE AND ISOLATION 



Yeasts are easily cultivated on decoctions of various fruits. Malt 

 extracts and fruit juices, such as prune juice together with decoc- 

 tions of carrots, potatoes, etc., make good media. Beer wort is the 

 best medium for the yeasts and the one which is most utilized for 

 their culture. It may be procured at breweries or prepared in the 

 laboratory after the following procedure: Soak 200 grams of malt, 

 which has been previously pounded, in a liter of cold water and bring 

 slowly to a temperature of 60 C. Shake once in a while, and after 

 three-quarters of an hour, add 4 grams of hops. Boil for about an 

 hour and filter. Test the nitrate for maltose by means of Fehling's 

 solutions. The nitrate is then diluted with distilled water to yield a 

 3 per cent solution of maltose. The wort is then filtered and steri- 

 lized at 115 for 20 minutes. 



The malt water is prepared by soaking 100 grams of germinated 

 barley, which has been previously boiled, in a liter of water. This is 

 then heated to 55-58 C. so that the amylase is not destroyed. Finally 

 it is boiled for 5 minutes and filtered for sterilization. 



Raisin extract is easily prepared by soaking a few grams of raisins 

 in a little water and filtering. The filtrate may be sterilized at 150 

 for 20 minutes. 



Another very useful medium is yeast water prepared as follows: 

 100 grams of fresh yeast are boiled, with shaking, in a liter of distilled 

 water. This is filtered and sterilized. Yeast water is made up of am- 

 monium salts, as paragin and peptones, which are ideal substances 

 for yeast growth. This liquid by itself is generally insufficient. In 

 order to secure abundant yeast growth, it is necessary to add a sugar. 

 The decoctions of meat and various peptone media are used for some 

 of the pathogenic yeasts. 



Yeasts grow equally well on solid media. It serves because they 

 sporulate easily in it and because they exhibit certain macroscopic 

 characteristics which are used in their determination. Slants of 

 potato, beet and especially carrot and even sterilized fruit juices are 

 excellent media. These may be solidified in media. Beer wort may 

 also be used as a solid medium. It is sufficient to mix 8 per cent of 

 gelatin with it. 



Methods for Obtaining Sporulation 



The study of sporulation among yeasts required a special tech- 

 nique which might be outlined at this time. Special conditions have 

 been mentioned above. The cells should be well nourished and young. 

 It is necessary that they have acquired a sufficient reserve in their 

 protoplasm to assure the formation of ascospores. It is necessary, 

 then, to cultivate the yeast which one wishes to study, in a nutrient 



