256 AGRICULTURAL BACTERIOLOGY. 



action of microorganisms. What part do they play in the 

 ripening of cheese ? This matter has been carefully studied by 

 Jensen as well as by Babcock and Russell. Their general con- 

 clusions are in agreement and are, essentially, as follows : 



In the ripening of both hard and soft cheeses these enzymes 

 play a part in producing the solubility of the casein. In the 

 soft cheeses it seems that the microorganisms, either bacteria 

 or yeasts, are of rather more importance than the enzymes, but 

 each contributes to the end reached. In the hard cheeses, at 

 least in the early part of the ripening, the enzymes, both the 

 galactase and the pepsin, are actively concerned in the increase 

 in the solubility of the casein. While these chemical ferments 

 are thus of much significance in the ripening, it does not appear 

 that they are alone concerned. - The ripening takes a long 

 time and during this period both the chemical ferments and 

 the microorganisms have an opportunity to produce their 

 effect. 



Agency of Bacteria. It is with the action of bacteria that 

 we are chiefly concerned, and while it is true that chemical 

 ferments are of much importance, it is equally certain that mi- 

 croorganisms are concerned in a very important manner in the 

 ripening of cheeses. In the first place there is a marked mul- 

 tiplication of bacteria in the cheese during the ripening. Bac- 

 teria do not find cheese so favorable a medium for growth as 

 cream, and their growth is much slower. This is probably 

 due to the more compact nature of cheese and the smaller 

 proportion of water that it contains. But that they do mul- 

 tiply in the cheese is shown by many analyses. In the study 

 of hard cheeses it appears that there are three periods of bac- 

 terial growth in the cheese-ripening. At first there is a decline 

 in the number of bacteria, continuing for about a day. This 

 is followed by an increase in bacteria which continues for two 

 or three weeks. This increase is due chiefly to the growth of 

 the lactic bacteria, for, while peptonizing bacteria are present, 



