612 BACTERIOLOGY OF MILK 



evidence of the relative salubriety of milk containing small numbers 

 of bacteria. The importance of a consistently low bacterial content 

 in milk designed for human consumption has been generally recog- 

 nized by city, state and national health bureaus, and the grading and 

 control of public milk supplies has been one of the great hygienic 

 questions of the last decade. The older conception of a chemical 

 standard to safeguard the financial interest of the consumer has been 

 broadened to include a bacteriological standard which aims to exclude 

 milk containing an excessive number of bacteria from the public 

 market. The bacterial standard adopted varies somewhat in different 

 cities, but in general it is so defined that all milk which meets its 

 requirements must of necessity be produced in clean dairies, handled 

 carefully and consistently maintained at a low temperature. The 

 bacterial standard is based upon the number of bacteria per cubic 

 centimeter of milk and it is rapidly becoming a custom to recognize 

 grades of milk, each of which must conform to certain regulations 

 regarding production, handling and bacterial count. 



Certified milk is the hygienic grade milk. It is usually the product 

 of a single dairy; the cows must be free from tuberculosis or other 

 disease and stringent regulations for the condition of the entire plant 

 are laid down. The milk as delivered must contain less than the 

 maximum number of bacteria per cubic centimeter, as set forth in 

 the standard. Usually the standard specifies 10,000 to 30,000 bacteria 

 per cubic centimeter. Certified milk is usually safe milk, but con- 

 tamination of it with human pathogenic organisms is not at all 

 impossible. Ordinary market milk is produced under less rigorous 

 conditions and the bacterial content is usually much greater; from 

 100,000 to 500,000 bacteria per cubic centimeter, or even 1,000,000 

 bacteria represent the usual standards enforced. 



Pasteurization of milk is rapidly becoming obligatory in many 

 cities, particularly for the ordinary grades of milk. Pasteurization is 

 carried out by heating milk to about 145 F. (the degree of heat 

 varies in different places), and maintaining it at that temperature for 

 thirty minutes. This degree and duration of heat is deemed sufficient 

 to weaken or destroy pathogenic organisms without altering the 

 nutritive value. The ideal method of pasteurization is to heat the 

 milk to the required temperature for the required time in the bottle 

 which goes to the consumer, thus entirely eliminating the danger of 

 human contamination subsequent to the process. 



The pasteurizing process does not kill many of the milk bacteria; 



