74 THE MILK QUESTION 



of the udder or by the act of milking, thus eliminating the danger 

 of pus cells in the milk. 



The significance of the number of bacteria in milk. Of all 

 the routine laboratory tests, the simple enumeration of the 

 number of bacteria in milk tells us most concerning its 

 general sanitary quahty. A large number of bacteria 

 in milk means that it is old, that it has not been kept 

 cold, or that it is dirty. The number of bacteria in milk 

 will depend upon any one of these three conditions: 

 time, warmth, or dirt. When the milk is old, warm, and 

 dirty, the numbers will be prodigious. Any combina- 

 tion of these three factors, or any one of the factors 

 operating alone, will result in an excessive number of 

 bacteria. 



The number of bacteria in milk cannot be taken as the 

 only index of its sanitary quality, although, generally 

 speaking, a milk that is rich in bacteria is undesirable for 

 human consumption and may be dangerous to infants and 

 children. The differences in sanitary importance of the 

 high and low bacterial counts are not proportionate to the 

 numerical differences. Under certain circumstances bac- 

 teria are purposely permitted to grow in milk until their 

 numbers are inconceivably great — over a billion per cubic 

 centimetre. This is the case with buttermilk and the vari- 

 ous sour-milk products which have recently become so 

 popular owing to the teachings of Metchnikoff that such 

 a diet prolongs life. This question will be discussed later. 

 It is plain, however, that large numbers of bacteria in 

 themselves may not be an infallible index of the sanitary 

 quality of the milk, for children stand buttermilk very 

 well, in fact, some physicians use buttermilk to correct 

 dietetic errors and summer complaints of babies. Butter- 

 milk, however, contains practically a pure culture of bac- 

 teria known to be harmless and purposely allowed to grow 

 and multiply in the milk and must not be confused with 

 the miscellaneous bacterial population ordinarily found 



