35° CLEAN MILK 



shown that cells are present in practically all samples of milk and that 

 in some samples the cellular content is much higher than is usual. 

 Where the number of cells is high it is customary to regard them as 

 pus cells, but there is no general agreement as to where the line should 

 be drawn. The question is a difficult one, because pus cells and dead 

 leucocytes are morphologically the same and so cannot be differen- 

 tiated by their appearance alone. Doane has proposed that milk shall 

 be regarded as containing pus if there is high cellular content accom- 

 panied by threads of fibrin. Bergey proposes that pus shall be diag- 

 nosed if there are 10 cells to the field of the 1-12 immersion lens. 

 Stewart centrifuges 1 c.c. of milk in small tubes and if he find 23 cells 

 to the field of the 1-12 immersion lens, when the sediment of this 

 amount of milk is spread over 1 square cm., he reports pus. Slack 

 proposes that the sediment of 2 c.c. milk shall be spread over 4 square 

 cm. and that pus shall be reported if 50 cells are seen to the 1-12 im- 

 mersion field. 



" Since there is much doubt, in many cases, as to whether high 

 cellular content actually denotes pus, — that is, as to whether the cells 

 found are pus cells or leucocytes, — and as to whether the cells them- 

 selves are injurious, it would appear to be desirable, for the present, 

 to report pus only where there is high cellular content, as judged by 

 one of the above methods, accompanied by the presence of strepto- 

 cocci." — Leonard Pearson, in Jensen's " Milk Hygiene." 



"It is evident that the whole subject is far from being on a satis- 

 factory basis. The various methods advocated give varying results 

 even on the same milk sample. Preheating of the milk to a high 

 temperature and also the height of temperature reached in such pre- 

 heating affect the result even when the same method is used. If a 

 specific maximum count is to be established as a limit, the specifications 

 must therefore include exact details of method, temperature and tech- 

 nique, to secure consistent and comparable results at the hands of 

 different workers under different conditions. No such standard has 

 yet been agreed upon. Moreover, normal cows sometimes give very 

 exceptionally high counts and this fact adds to the difficulties in de-, 

 termining an absolute standard." — W. H. Hill. 



