BACTERIOLOGICAL STUDY OF MILK. 647 



not remains to be demonstrated. The several milk 

 commissions composed of pediatrists in various large 

 cities have established a bacterial standard for pediatric 

 milk of 10,000 bacteria to the cubic centimetre. Expe- 

 rience has shown that it is possible to market milk that 

 meets this bacterial standard sometimes with merely 

 ordinary precautions with regard to cleanliness. In 

 larger dairies it has frequently been a question of some 

 difficulty on account of the elaborate scale on which 

 everything is conducted. 



QUANTITATIVE BACTERIOLOGICAL ANALYSIS. In 

 the quantitative bacteriological examination of market 

 milk it is necessary to dilute the milk with sterile water 

 or sterile salt solution before plating on account of the 

 very large numbers of bacteria present. The degree 

 of dilution that is necessary will depend upon the 

 nature of the dairy from which the milk is derived, the 

 age of the milk, and the temperature at which it has 

 been kept. Usually a dilution of 1 to 100, 1 to 1000, 

 and 1 to 10,000 is sufficient. From these dilutions 

 plate cultures are made with 0.1, 0.2, 0.3 cubic centi- 

 metre of each dilution. 



QUALITATIVE BACTERIOLOGICAL ANALYSIS. 

 Aside from the quantitative bacteriological analysis of 

 milk the qualitative analysis has received a great deal 

 of attention. Detailed qualitative analysis necessarily 

 entails an enormous amount of labor, but the detection 

 of certain forms of bacteria is not always very difficult. 

 This applies especially to the detection of streptococci. 



Since milk containing streptococci in considerable 

 numbers is derived from the udder of a cow suffering 

 from some form of mastitis, it is always possible to find 

 pus in such milk. Consequently it is customary to 



