214 Dairy Bacteriology. 



milk. When more than three hours elapse before the 

 disappearance of the blue color, the bacterial content is 

 low and the milk is to be placed in the highest grade. 



The time of reduction is only a rough index of the 

 number of bacteria present, but it gives a good idea of 

 the keeping quality of the milk, and of the conditions of 

 production and handling. Of the above tests the sedi- 

 ment and acid tests are more frequently used. 



Examination of milk sediments. In the modern mu- 

 nicipal laboratory, efforts are made to determine, as far 

 as possible, the conditions of production on the farms, 

 by an examination of the milk in the laboratory. The 

 samples of milk are sedimented in a small centrifuge, 

 and an examination of the sediment made with the 

 microscope. The types of bacteria and the number of 

 body cells found is an indication as to whether any of 

 the animals of the herd are suffering from inflammation 

 of the udder. The test, also gives information similar 

 to the dirt test since the insoluble dirt will be thrown 

 down and will impart a color to the sediment. 



Pasteurization of market milk. The spread of the 

 pasteurizing process as applied to market milk has been 

 rapid. This has been due to the recognition of the fact 

 that only by this process can a safe milk i. e., one free 

 from pathogenic bacteria, be obtained. As previously 

 mentioned a small proportion of all human beings that 

 have suffered, from typhoid fever become bacillus car- 

 riers. It is impossible to examine all persons who may 

 be concerned in the handling of milk in order to ascer- 

 tain whether they belong to this dangerous and unfor- 

 tunate class of people. 



The larger cities have also recognized the impossibil- 

 ity of requiring the tuberculin test of all cattle furnish- 



