Bacteria in Cheese. 167 



to be found. The quantity of these lower products in- 

 creases with the age of the cheese. 



The chemical reaction of cheese is normally acid to 

 phenolphthalein, although there is generally no free acid, 

 as shown by Congo red, the lactic acid being converted 

 into salts as fast as formed. In very old cheese, undergo- 

 ing putrefactive changes, especially on the outside, an alka- 

 line reaction may be present, due to the formation of free 

 ammonia. 



The changes that occur in a ripening cheese are for the 

 most part confined to the proteids. According to most in- 

 vestigators the fat remains practically unchanged, although 

 the researches of Weigrnann and Backe l show that fatty 

 acids are formed from the fat. In the green cheese con- 

 siderable milk-sugar is present, but, as a result of the fer- 

 mentation that occurs, this is rapidly converted into acid 

 products. 



Bacterial flora Of Cheese. It might naturally be expected 

 that the green cheese, fresh from the press, would contain 

 practically the same kind of bacteria that are in the milk, 

 but a study of cheese shows a peculiar change in the char- 

 acter of the flora. In the first place, fresh cottage cheese, 

 made by the coagulation of the casein through the action 

 of acid, has a more diversified flora than cheese mada with 

 rennet, for the reason, as given by Lafar, 2 that the fermen- 

 tative process is farther advanced. 



When different varieties of cheese are made from milk in 

 the same locality, the germ content of even the ripened 

 product has a marked similarity, as is illustrated by 

 Adametz's work 3 on Emmenthaler or Swiss hard cheese, 



1 Milch Zeit., 1898, No. 49, 



2 Lafar, Technical Mycology, p. 21t>. 

 8 Adametz, Landw. Jahr., 18: 228. 



