YEASTS AND OIDIA IN PASTEURIZED BUTTER 135 



Whey agar is prepared as follows: Skimmilk is warmed 

 to about 100 F., acidified with lactic or hydrochloric acid, 

 coagulated with rennet or pepsin, the curd is cut, allowed 

 to settle and then heated to 115 C. in the autoclave, the 

 whey is filtered off through cotton, neutralized, made up 

 with 1.5 per cent agar, 1 per cent peptone, and filtered. In 

 plating, 1 c. c. of sterile 1 per cent tartaric acid solution (by 

 weight) is placed in the petri dish. Then 1 c. c. or 1 gram 

 of the material to be analyzed is introduced. With this is 

 mixed 10 c. c. of the agar. In two or three days at room 

 temperature the yeast colonies are about 3 mm. in diameter, 



Fig-. 2. Yeasts and Oidia (Left) 1 c. o. of inefficiently pasteurized cream plated in 

 whey tartaric acid agrar. (Bight) In 1 c. c. of butter plated in whey tartaric acid 

 agar. 



raised, moist, and glistening. The Oidium colonies are about 

 1 to 3 cm. in diameter, dry and velvety. One soon learns to 

 recognize them at once with the unaided eye (see Fig 2). 

 Mixed colonies occur, but they do not affect the practical 

 interpretation of the count. Colonies of bacteria seldom 

 reach such a size as to interfere. Occasional air molds are 

 regarded as an accidental contamination unless they recur 

 in considerable numbers in the subject from the same source. 

 Professor Lund has successfully used beerwort and lactic 

 acid instead of whey and tartaric acid. Where obtainable, 

 the wort is more convenient than whey. 



We have not made any study of the species or races of 

 yeasts and Oidia that occur here. We are unable to give any 



