258 AGRICULTURAL BACTERIOLOGY. 



sequently contribute to the ripening. It is a matter of com- 

 mon experience that the cheese becomes acid during the 

 progress of normal ripening. The milk sugar largely dis- 

 appears and a variety of acids appear, part of which are doubt- 

 less due to the growth of the lactic bacteria. Lastly, practical 

 experiments have shown that cheese made from milk inocu- 

 lated with lactic bacteria ripens normally, while such a result 

 does not appear when it is inoculated with other types of bac- 

 teria. All of these facts lead to the conclusion, generally 

 accepted to-day, that in cheese-ripening, as in cream-ripening, 

 the lactic bacteria are chiefly concerned. But whether they play 

 an important part or a small part in producing the chemical 

 changes of ripening cream is not yet fully determined. 



2. THE PRODUCTION OF FLAVOR. 



The important agency of microorganisms in the ripening 

 of cheese is in the production of the flavor. Cheese is eaten, 

 not because of its nutritive value, although doubtless it is 

 one of the most nutritious of foods, but because of its flavor. 

 The popularity of cheese in so many races of men is due to 

 the fact that it has a strong, appetizing taste which gives relish 

 to other foods. Although physiologists recognize no food 

 value in flavors, they realize perfectly well that they are of the 

 greatest significance in diet, inasmuch as they greatly aid in 

 properly stimulating the digestive functions to handle food. 

 A diet of tasteless food cannot be digested and assimilated. 

 The high flavors of cheese are consequently a great boon to 

 mankind, especially among the poorer classes who must live 

 largely upon coarse foods. Even the coarsest bit of dry bread 

 may be made palatable by the aid of a little cheese flavor to 

 give it a relish. Thus the cheese flavors give this material its 

 peculiar value as a food product. The origin of these flavors 

 is therefore a matter of the greatest importance. 



Although the chemical changes which digest the casein in 



