ix] CHEESE 151 



house cheese, 5,600,000. Their number has been 

 found to increase slowly during the ripening process. 

 That these bacteria belong to various species seems 

 to be evident. It seems also pretty conclusively 

 proved that every kind of cheese has to be ripened 

 by a definite species ; but the difficulty is in identi- 

 fying the specific kinds of ferments connected with 

 the different kinds of cheeses, that perfect ripening 

 requires the united action of many different species 

 of bacteria, the action of which upon one another is 

 of a very complicated nature. Certain cheeses, again, 

 not only require various kinds of bacteria in their 

 preparation, but also certain moulds. Some of them 

 are aerobic, while others are anaerobic. How far the 

 characteristic properties of different kinds of cheese 

 are respectively due to the action of one specific class 

 of bacteria is not absolutely certain. There seems to 

 be strong evidence, however, that this is the case ; since, 

 as the ripening process goes on, one species generally 

 increases at the expense of others. As the bacteria 

 concerned in the ripening of cheese are always present 

 in milk, the art of cheese-making consists in producing 

 circumstances which will favour the predominant de- 

 velopment, of that class of bacteria, specially impli- 

 cated in the ripening of the particular kind of cheese 

 to be made. A ferment, made by the bacteria which 

 ripen cheese, has been isolated and studied by 

 Duclaux : he calls it casease. 



