CHAPTER XXIX 



BACTERIA OF MILK AND ITS PRODUCTS (Continued) 



The Species of Bacteria in Milk. Of the bacteria which 

 get into milk there are a good many different species. They 

 may be grouped in the present consideration into those bac- 

 teria which produce little or no change in the milk, even though 

 they may multiply to a considerable extent, and this would 

 include the bacteria usually found in the udder, most of the 

 bacteria from the air, etc. Another group of bacteria pro- 

 duce certain fermentations in the milk, causing the precipi- 

 tation of the casein due to the formation of acids and enzymes, 

 the production of gas which interferes with the use of milk 

 for the manufacture of cheese, or the production of disagree- 

 able odors and tastes and unnatural colors, and even sliminess. 

 Another group of bacteria that sometimes get into milk are 

 disease-producing. 



Lactic Acid Bacteria. Lactic acid bacteria always find 

 their way into mill^. They get into the milk usually from some 

 contaminating influence, and the number that get in may be 

 very 'small, but the lactic acid bacteria find milk the culture 

 medium par excellence, and although they are few in number 

 at first they soon outgrow the other forms, and milk left to it- 

 self almost invariably undergoes lactic acid fermentation. 



