Introduction 



10,000 in six hours; 10,000,000 in nine hours, 

 and 2,000,000,000 in eighteen hours. As the 

 bacteria grow and increase in numbers they 

 impair the nutritive properties of the milk, 

 and in this way injure it as a food, and, what 

 is much more important, they produce many 

 new substances, some of which are poison- 

 ous. It is the result of the activities of bac- 

 teria which causes milk to sour and produces 

 in it bad taste and odors. But long before 

 milk has become sour to the taste, it may 

 contain enormous numbers of bacteria and 

 has usually become unwholesome, and pro- 

 bably a source of great danger. The number 

 of bacteria which may be found in milk is 

 almost beyond belief. This is directly pro- 

 portionate to the age of the milk, the amount 

 of dirt and filth it contains, and the height 

 of the temperature at which it has been kept. 

 The number of bacteria is, therefore, the best 

 means of determining whether the milk is 

 clean and fresh and whether it has been 

 properly handled, and it tells with certainty 

 the story of mistakes or neglect. 



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