BACTERIA IN CHEESE RIPENING. 227 



results that are obtained inevitably differ. Until there can be 

 a large series of studies upon a great variety of cheeses and 

 the whole can be properly compared, it will be impossible to 

 reach general conclusions as to the phenomena of cheese 

 ripening, or make any general statements as to the compara- 

 tive significance of enzymes and microorganisms. 



Nevertheless many facts demonstrate the importance of 

 microorganisms in the ripening. There is a marked increase 

 in bacteria in the cheese during the ripening. The growth 

 of bacteria during cheese ripening, however, is much slower 

 than it is during cream ripening. Cheese contains only a 

 comparatively small amount of water, and is a compact, 

 usually somewhat hard, dense mass, from the interior of 

 which oxygen is, to a large extent, excluded. Under these 

 conditions the growth of bacteria is much slower than in 

 cream. Nevertheless, they do develop abundantly. In the 

 different types of cheeses the growth of the bacteria is not 

 always the same. In some cheeses there is, for a day or two, 

 a marked decline in number of bacteria, followed by a rapid 

 rise, continuing for some days. This is followed eventually 

 by a slow decline, until the number becomes very small. In 

 other cases no initial decline has been found, the bacteria 

 from the beginning multiplying rapidly, rising to a high 

 number in the course of three to four days, and then declining, 

 at first rapidly, and then much more slowly, until, in the end, 

 the number is quite small. In the common Cheddar cheese, 

 for example, the number may, in the course of three days, 

 rise to about 450,000,000 per gram, a number which is about 

 as high as it is in some samples of ripened cream. This 

 number later falls off and eventually reaches a million or so 

 per gram. Usually, however, the number does not rise as 

 high as this, and even these numbers are less than are found 

 in cream which has ripened a couple of days. 



In cheese ripening, as in cream ripening, it is chiefly the 

 lactic bacteria that grow (267). The enzyme- forming bac- 



