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 ¢. ¢. of sterile 1 per cent tartaric acid solution (by 
weight) is placed in the petri dish. Then 1 ¢. ¢ or 1 gram 
of the material to be analyzed is introduced. With this is 
mixed 10 ¢. ¢. 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 ¢. ¢. of inefficiently pasteurized cream plated in 
pened tartaric acid agar. (Right) In 1 ¢. ¢. of butter plated in whey tartaric acid 
raised, moist, and glistening. The Oidium colonics are about 
1 to 3 em. in diameter, dry and velvety. One soon learns to 
recognize them at once with the unaided eve (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 suecessfully 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 
