60 Dairy Bacteriology. 



pecially if surface drainage from the factory is possi- 

 ble, the water may be contaminated to such an extent 

 as to introduce undesirable bacteria in such numbers 

 that the normal course of fermentation may be 

 changed. The quality of the water, aside from flavor, 

 can best be determined by making a curd test (p. 99) 

 which is done by adding some of the water to boiled 

 milk, and incubating the same. If "gassy'' fermenta- 

 tions occur, it signifies an abnormal condition. In deep 

 wells, pumped as thoroughly as is generally the case 

 with factory wells, the germ content should be very 

 low, ranging from a few score to a few hundred bac- 

 teria per cubic centimeter at most. The danger from 

 ice is much less, for the reason that good daily prac- 

 tice does not sanction using ice directly in contact with 

 milk or cream. Then, too, water is largely purified 

 in the process of freezing, although if secured from a 

 polluted source, reliance should not be placed in this 

 method of purification, for even freezing does not de- 

 stroy all vegetating bacteria. 



The ordinary house fly is an important source of con- 

 tamination in creameries, cheese factories and city milk 

 plants. They are of importance not only in increasing 

 the number of fermentative bacteria in milk but they 

 may serve to contaminate it with disease-producing or- 

 ganisms. The windows of all places where milk is han- 

 dled, whether on the farm or elsewhere should be 

 screened. 



It should be kept in mind in the handling of milk and 

 other dairy products that human food is being prepared 

 and that cleanliness is desirable from every point of 



