CHAPTER IV. 



THE FERMENTS AND FERMENTATIONS OF MILK, 

 AND THEIR CONTROL. 



Milk, when it is first drawn, is a limpid fluid 

 with a slight odor, mildly sweetish taste, and faint 

 alkaline reaction. In fact, milk often shows the 

 amphoteric reaction ; that is, it will give the acid 

 reaction with blue litmus paper and the alkaline 

 reaction with red. Almost immediately after it is 

 drawn, milk begins to undergo a change, and within 

 a short time will show a distinct acid reaction. 

 The degree of aciditj^ increases with the age of the 

 milk. Soon changes begin in the other milk con- 

 stituents, and in a comparatively short time, the de- 

 composition is so great that the milk can no longer 

 be used for food. The sugar is the first constit- 

 uent of the milk to undergo change, afterwards 

 the albuminoids are attacked, and lastly the fats. 

 These changes are not due to any instability of the 

 organic compounds in the milk, but to the effect 

 of various vegetable germs that gain access to the 

 milk after it is secreted, and, living and growing 

 in the milk, bring about the changes mentioned. 

 These changes are called fermentations, and the 

 agents that bring them about ferments. Milk con- 

 taining no germs of fermentation, or milk from 



