THE HARD CHEESES. 199 



ditions, which is responsible for the chemical changes that take 

 place in the ripening cheese. This conclusion, however, has not 

 been very generally accepted; for while the lactic acid bacteria, 

 under these conditions, do produce a certain amount of peptoniza- 

 tion of the casein, the action is extremely slow and not very complete; 

 and it has not seemed to most students that the phenomenon in 

 question is sufficiently explained by this slow action of the lactic acid 

 bacteria. 



Flavor Production by Bacteria. Apparently the flavors must 

 be due to bacterial action. Cheeses ripened in chloroform vapor, 

 whidh allows the enzymes to act, but prevents bacteria from growing, 

 though they ripen, do not develop flavors and these must be due to 

 some other cause than enzyme action. That they are the end- 

 product of chemical decomposition seems to be extremely probable. 

 In many cases they are associated with ammonia; and ammonia, as 

 is well known, is one of the final products of proteid destruction. 

 The only known agency that commonly produces the complete 

 destruction of proteids is bacterial, and, while the matter has never 

 been put to any satisfactory test, the most probable explanation 

 seems to be that these cheese flavors are the result of bacterial 

 decomposition. 



Against this view, however, has been urged the fact that in the 

 well ripened cheeses hardly any bacteria, except lactic acid organisms, 

 are present, and that this class of bacteria does not, so far as is 

 known, have any power of producing cheese flavors. Some 

 bacteria, if they grow in proper abundance in milk, will in time 

 develop well-known cheese flavors; but these organisms have not 

 been found in old, strongly flavored cheeses. Whether they have 

 anything to do with the production of cheese flavors is, therefore, 

 uncertain. It has been suggested that the flavor of cheeses may be 

 due to the bacteria which grow in them during the first few days. 

 Liquefying bacteria are found during this early period, and before 

 the miscellaneous bacteria disappear, as they do later, some of these 

 liquefiers may secrete from their bodies substances, possibly enzymes, 

 that continue their action in the cheese, slowly, but for a long time. 

 Although the bacteria that produce them soon die, the chemical 



