332 MICROBIOLOGY OF MILK AND MILK PRODUCTS. 



it was assumed that they showed the presence of inflammation and pus formation in the 

 udders of the cows producing the milk. 



Several methods have been used for determining the leucocyte content of milk. 

 "The Smear Sediment" and "Blood Counter" are methods which more strictly belong 

 to laboratory practices and will not be considered in this place. 



BACTERIOLOGICAL MILK STANDARDS. 



Thtyelation of the bacterial content of milk to its wholesomeness has 

 led to the adoption of certain standards by the boards of health in our 

 cities. These standards recognize the fact that the germ content of milk 

 in the large cities is greater than in the smaller ones because of the greater 

 distance from which it is shipped and its age on arrival in the city. New 

 York City in 1900 adopted a maximum limit of 1,000,000 per c.c. Later 

 Boston established a limit of 500,000. Chicago's limits are 1,000,000 

 from May to September, inclusive, and 500,000 from October to April, 

 inclusive. Rochester's standard is 100,000. Other cities have similar 

 standards. 



Stokes' standard for the number of leucocytes permissible in normal 

 milk was 5 per field of the 1/12 objective in his smeared sediment prepara- 

 tion. Bergey found so many samples running above this number that 

 he made the limit 10 cells per field and felt that no milk containing more 

 than this number should be used for food. Later Slack raised the limit 

 to 50 cells per field. The reason for changing the standard was due partly 

 to the larger numbers found as a result of improved methods but more 

 especially to the discovery that milk from apparently healthy cows nor- 

 mally contains leucocytes in excess of the first standards set. 



It is held by some that a numerical standard is of little value since the 

 actual number of organisms present in a given lot of milk may not be a 

 correct measure of its wholesomeness. For this reason some cities pay 

 little attention to the numbers of bacteria present but base their stand- 

 ards wholly on the species, and the quality of the milk is judged on the 

 presence and numbers of streptococci, B. coli, leucocytes, sediment. 

 Milk is passed or condemned on the basis of any one or combination of 

 these conditions. 



In recent years there has been a tendency to combine these two 

 standards using the total germ content as a measure of the care the milk 

 has had and the presence or absence of certain groups or species as an 

 indication of the occurrence of pathological conditions in the cows pro- 

 ducing the milk. The practice in most city laboratories now is to make 



