EXAMINATION FOE DIRT 235 



are morphologically the same and so can not be differ- 

 entiated by their appearance alone. . Doane has pro- 

 posed that milk shall be regarded as containing pus if 

 there is high cellular content accompanied by threads 

 of fibrin. Bergey proposes that pus shall be diagnosed 

 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 immersion 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 leuco- 

 cytes, and as to whether the cells themselves are in- 

 jurious, 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 streptococci. L. P.] 



/. Examination for dirt. The sale of unclean or dirty 

 milk should be forbidden. A number of cities in Ger- 

 many have established the requirement that milk shall 

 not contain over a definite amount of dirt ; the limit va- 

 ries from 5 to 10 milligrams of dry dirt to a liter of milk. 

 An examination for dirt can be made as follows : The 

 milk is placed in bottles, which are centrifuged, the milk 

 is decanted and the sediment is dried at a temperature a 

 little above that of boiling water. This material is 

 weighed and its quantity per liter is calculated. 



Instead of this rather formidable method it is usu- 

 ally sufficient to centrifuge the milk and then measure 

 the sediment. Or, one can pour the milk in a high glass 

 of conical shape and ascertain the amount of sediment 



