82 THE MILK QUESTION 



ary power of fresh milk to restrain and retard the growth 

 of bacteria. The fact that the jgermicidal action of milk 

 must be very feeble may be guessed a priori from the fact 

 that bacteria grow in the perfectly fresh milk in the milk 

 cistern and ducts of the mammary gland. 



The restraining action is specific, at most is very fee- 

 ble, and is destroyed if milk is heated above 80 C. The 

 germicidal action varies in different animals and in the 

 milk from the same animal at different times. It cannot 

 take the place of cleanliness and ice, but may be taken 

 advantage of in good dairy methods. 



The power of fresh milk to restrain the growth of bac- 

 teria corresponds to a similar power possessed by the blood 

 and other important fluids in the body. The germicidal 

 action of milk is one of the chief reasons why fresh milk is 

 so much better than milk twenty-four hours or more old. 



Pasteurization is sometimes objected to for the reason 

 that the heat destroys this germicidal power and for the fur- 

 ther reason that the bacteria grow better in heated milk 

 than in raw milk. As a matter of fact, the temperature at 

 which milk should be pasteurized has very little influence 

 upon the germicidal activity. Further, this power has long 

 ceased to operate when the average market milk reaches 

 the city. Bacteria grow quite as quickly in raw milk twenty- 

 four hours old as in heated milk. 



Why milk spoils and how 



Milk left alone ordinarily turns sour and curdles. This 

 occurs in the great majority of instances and is therefore 

 called the normal method. It is not " normal " in any sense 

 except that it is the usual form of fermentation which takes 

 place when milk is left to itself. When we examine into 

 this subject a little more closely we find that milk will spoil 

 in a great variety of ways. The cause of the changes which 

 take place in milk is always due to the action of micro- 

 organisms, but the kind of deterioration depends upon the 



