96 MILK - [vi 



casein and milk-sugar in various ways, and is con- 

 sequently not to be regarded as a uniform process, it 

 is best not to adopt this method of classification. 



Casein Ferments. Just as we have a class of 

 ferments which act upon the milk-sugar, so we have 

 a class that decompose the casein. To the latter class 

 the name casein ferments has been applied. This order 

 of bacteria have also the power of coagulating the 

 milk, not, like the lactic ferments, by the production 

 of lactic acid, but by the production of a rennet-like 

 substance. As belonging to them may be men- 

 tioned the Tyrothrix tenuis, which has been studied 

 by Duclaux ; and a ferment which Conn has suc- 

 ceeded in preparing in the form of a powder, and which 

 acts like rennet ferment. Some of these ferments have 

 the power of redissolving the curdled milk by means 

 of second ferments. They play an important part in 

 the ripening of cheese, and the decomposition of 

 the casein which they initiate is of a most com- 

 plicated character, and is accompanied by the 

 production of such substances as peptone, leucin, 

 tyrosin, and butyric acid. Among them are the 

 hay and potato bacilli, and a number of so-called 

 butyric ferments. Those best known are those which 

 have been studied by Duclaux, to which he has given 

 the name Tyroihria, and of which eight or nine differ- 

 ent kinds have been identified. The casein ferments, 

 unlike the lactic ferments, are for the most part spore- 



