[ 757 1 



are difficult to kill in the milk and these account for the diffi- 

 culty in sterilizing milk. The commonest of these is the 

 Tyrothrix tenuis of Duclaux. It can stand a temperature of 

 239 to 248 F. Cultivated in milk at a temperature of 98iF 

 it is capable of curdling milk, the curdles formed being re- 

 dissolved afterwards by the action of the same bacillus. The 

 decompositions effected by this bacillus result in the produc- 

 tion of peptone, leucin, tyrosin, ammonia, butyric acid &c. 

 Other bacteria also play a part in caseous fermentation, and 

 probably still others in the ripening of cheese. It has been 

 noticed that cheese does not ripen properly if the milk is 

 pasteurised, or if boiled or sterilized milk is used before the 

 addition of rennet. Such milk loses most of the bacteria 

 some of which are helpful in the ripening of cheeses. But the 

 bacteria helpful in the ripening of cheeses have not been 

 isolated, and no improvement in the ripening of cheese, 

 due to the addition of pure cultures of specific bacteria, has 

 been as yet effected. Besides it is doubtful whether there 

 are any specific bacteria which help in the ripening of cheeses, 

 or whether the lactic and the caseous bacteria are not helpful 

 to the ripening also. 



1,310. Kephir. There is a Saccharomyces (S. lactis) 

 which is able to convert milk-sugar into alcohol and carbonic 

 acid gas, and very little lactic acid. Kephir is the name of 

 a fermented beverage made out of cow's milk by the addition 

 of what is known as ' Kephir grains' which consist of 

 fungi which include the Saccharomyces lactis, also a gela- 

 tinous filamentous Bacterium known as Dispora caucasica 

 and the commonest bacterium of lactic acid. One volume of the 

 grains are added to 7 volumes -of fresh milk and the mixture 

 exposed to air for 24 hours, protected from dust by the 

 loose covering of a cloth, and shaken from time to time. 

 The milk is then strained off from the grain and is mixed 

 up with twice the quantity of fresh milk, bottled, corked 

 and stirred from time to time. This is drunk in 2 or 



