122 Report of the Department of Bacteriology of the 



This method of milk examination was later improved by Bergey, 4 

 Stewart 5 and Slack. 6 The final improved form of the Stokes method 

 is commonly spoken of as the " smeared-sediment " method of milk 

 examination. It has been generally used in a number of American 

 laboratories for routine examinations, and is recommended by the 

 Committee on Standard Methods of Bacterial Milk Analysis 7 

 appointed by the American Public Health Association. 



About the same time Doane and Buckley 8 devised a modifica- 

 tion of the ordinary method used in counting the number of red 

 and white blood cells which they used for counting the cells in milk. 

 In this so-called " volumetric " method, 10 cubic centimeters of 

 milk was centrifuged and a suspension prepared from the sediment 

 obtained. This suspension was examined in the counting chamber 

 of a Thoma-Zeiss haemocytometer and the cells counted. The cell 

 counts thus obtained proved to be higher than those obtained by 

 the use of the smeared-sediment method. 



This " volumetric " method was later modified by Russell and 

 Hoffmann 9 who found that a preliminary heating of the milk to 

 70 degrees C. enabled them to secure higher and more consistent 

 counts. This modified form of the " volumetric " method is recom- 

 mended by the Committee on Standard Methods already referred 

 to as being more accurate but less convenient to use for routine 

 work than the smeared-sediment method. 



A number of American investigators have used one or both of 

 these methods to determine the number of cells present in milk 

 and an extended discussion of their sanitary significance has been 

 carried on. Some of the papers which have been written have already 

 been referred to. Other papers are those of Ward, Henderson and 



4 Bergey, D. H. The cellular and bacterial content of cows' milk at different periods 



of lactation. Univ. of Penn. Med. Bui., 17 : 181-182, 1904. Idem. Source 

 and nature of bacteria in milk. Dept. Agri. Commonwealth Penn., Bui. 125: 

 1-40, 1904. 



5 Stewart, A. H. Methods employed in the examination of milk by city health 



authorities. Amcr. Med., 9 : 4S6-488, 1905. 



6 Slack, F. H. Methods of bacteriological examination of milk. Jour. Inf. Dis., 



Supple. 2:214-222, 1906. 

 7 Amer. Jour. Pub. Hyg,. 20 (N. S. 6) : 315-345, 1910. 



8 Doane, C. F. Leucocytes in milk at?d their significance. Md. Agr. Exp. Sta., Bui. 



102 : 205-223, 1905. 



9 Russell, H. L. and Hoffmann, C. Effect of heating upon the determination of 



leucocytes in milk. Amer. Jour. Pub. Hyg., 18 (N. S. 4) : 285-291, 1908. 



