120 BACTERIOLOGICAL METHODS 



isms permissible. The only quality test made by the Bureau of 

 Chemistry is for the colon bacillus. 



15. The Microscopical and Bacteriological Examination of Milk 



It is not practicable to enter into a discussion of the dairying 

 industry or the multitudinous factors which cause modification of 

 the quality of cow's milk. These are matters which concern the 

 food bacteriologist but little. Bovine diseases, inclusive of tuber- 

 culosis, must be left to the veterinarian and the making of dairy 

 products concern the manufacturer primarily. By this it is, how- 

 ever, not intended to imply that the food bacteriologist need not 

 have intimate knowledge of cattle diseases and of dairying meth- 

 ods. Not only should he be well informed regarding these things 

 but he should be qualified to examine cattle for diseases, tubercu- 

 losis in particular, and should be prepared to examine and report 

 upon the sanitary conditions, equipment and the moderness of dai- 

 rying establishments. However, the chief efforts of the food bac- 

 teriologist are devoted to the examination of the milk and dairying 

 products as they appear upon the market. 



For the present purpose it will suffice to give a mere outline of 

 the methods of examining and testing milk microscopically and 

 bacteriologically. The report of the analysis should comprise the 

 following. 



Securing the sample. 

 Sealing the sample. 



Keeping sample on ice until ready for examination. 

 Examining the sample. 

 Direct examination. 



Determining the fat content by the microscopical method. 

 Quantitative determination of 

 Bacteria. 

 Epithelial cells. 

 Blood corpuscles. 

 Pus cells and leucocytes. 

 Plate cultures. 



Presumptive colon bacillus test. 

 Numerical count. 



