436 CITY MILK SUPPLY 



of the cellular content, and the bacteria. For the former the methods 

 of Prescott and Breed, of Doane and Buckley as improved by Hastings, 

 or of Stewart are used. Of the three the Stewart method is the least 

 exact. However, it is the most convenient and the information obtained 

 from the microscopical examination of the smeared sediment, although 

 it is not accurate enough for quantitative work, is satisfactory for 

 qualitative examinations and so has proved very helpful in routine labora- 

 tory practice. Slack first advocated a microscopical estimate of bac- 

 teria by an adaptation of the Stewart method for cells. The method of 

 Prescott and Breed shows the greatest number of cells and has the ad- 

 vantage that the smear can be used also for microscopical counting of 

 bacteria. 



Stokes and Wegefarth in 1897 called attention to the leukocytes in 

 market milk and took the ground that milk containing more than five 

 leukocytes to a field of a 2-mm. objective was unfit for use. They spoke 

 of the leukocytes as pus cells and the inference was widely drawn that 

 the presence of large numbers of these cells indicated that the milk came 

 from cows with inflamed udders. Subsequent investigations showed 

 this view to be fallacious; cows giving no history of udder trouble and 

 in perfectly normal health were found to give off body cells which are 

 mostly leukocytes but partly epithelial cells, at times in great numbers. 

 The leukocytes themselves occur normally in the blood and lymphatics 

 and make their way from these into most of the other body tissues so 

 that they can be correctly spoken of as pus cells only when they can be 

 shown to be derived from suppurative discharges. 



It is generally accepted that if the Stewart-Slack smear shows the 

 intimate association of long-chain streptococci with bunched leukocytes, 

 it may be safely concluded that the organisms are pyogenic streptococci 

 derived from cases of garget and that the milk should be withheld from 

 the market until the affected animals are located and removed from the 

 herd. The health department of the city of Boston, Mass., began ex- 

 cluding milk from the city on this test in 1905. That year 10.5 per cent, 

 of the 5,500 samples of market milk examined were found infected with 

 the streptococci. At that time milk was excluded that showed "pus" 

 without streptococci or streptococci without "pus," later a more conserva- 

 tive attitude was taken and only milk showing pus, or bunched leukocytes 

 associated with streptococci was excluded. In 1906 the number of 

 positives dropped to 4.9 per cent, and in 1907 to 1.1 per cent, and has 

 remained less than 2 per cent, ever since, usually being about 1 per 

 cent. Many times the justice of the Board's action has been confirmed 

 by tracing the milk back to the farm that supplied it and finding cows 

 with diseased udders in the herd. 



In making bacterial counts by his method, of milk brought in by 

 farmers, Breed very recently has found enormous numbers of long 



