THE RELATION OF MICROORGANISMS TO MILK 405 



Stokes' standard for the number of leucocytes permissible in normal 

 milk was 5 per field of tte J^2 objective in his smeared sediment prepa- 

 ration. 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 stand- 

 ard was due partly to the larger numbers found as a result of improved 

 methods but more especially to the discovery that milk from appar- 

 ently healthy cows normally contains leucocytes in excess of the first 

 standards set. 



With the development of the dairy score card, there was a decided 

 tendency to place emphasis on the sanitary conditions at the farm rather 

 than on the germ content of the milk. But it was soon discovered that 

 the farm score did not necessarily show the true condition of the milk, 

 and at present, the tendency seems to be toward placing more confidence 

 in the germ content as the best measure of the true conditions of pro- 

 duction and handling. However, the fact must be recognized that our 

 methods of bacteriological analysis are not sufficiently accurate to 

 justify the bacteriologist in passing judgment concerning the quality of 

 any milk supply on a single analysis. In order to secure results which 

 are at all trustworthy, a series of analyses must be considered. 



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 

 standards 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 

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

 make use of both the numbers and the species present in determin- 

 ing the quality of the milk supply. 



