RELATION OF BACTERIA TO DAIRY INDUSTRY. 89 



the whole process to a bacterial fermentation 

 leads us to believe at the outset that some of 

 the differences in character are due to different 

 kinds of bacteria that multiply in the cheese and 

 produce decomposition therein. 



When the matter comes to be studied by bac- 

 teriology, the demonstration of this position be- 

 comes easy. That the ripening of cheese is due 

 to growth of bacteria is very easily proved by 

 manufacturing cheeses from milk which is de- 

 prived of bacteria. For instance, cheeses have 

 been made from milk that has been either ster- 

 ilized or pasteurized which processes destroy 

 most of the bacteria therein and, treated other- 

 wise in a normal manner, are set aside to ripen. 

 These cheeses do not ripen, but remain for months 

 with practically the same taste that they had 

 originally. In other experiments the cheese has 

 been treated with a small amount of disinfective, 

 which is sufficient to prevent bacteria from grow- 

 ing, and again ripening is found to be absolutely 

 prevented. Furthermore, if the cheese under or- 

 dinary conditions is studied during the ripening 

 process, it is found that bacteria are growing dur- 

 ing the whole time. These facts all taken to- 

 gether plainly prove that the ripening of cheese 

 is a fermentation due to bacteria. It will be 

 noticed, however, that the conditions in the 

 cheese are not favourable for very rapid bac- 

 terial growth. It is true that there is plenty 

 of food in the cheese for bacterial life, but the 

 cheese is not very moist; it is extremely dense, 

 being subjected in all cases to more or less pres- 

 sure. The penetration of oxygen into the centre 

 of the mass must be extremely slight. The dens- 

 ity, the lack of a great amount of moisture, and 



