THE DETECTION OF PASTEUPwIZED MILK 153 



Lacking definite evidence to the contrary and in keeping 

 with common practice, these cells will be referred to as leu- 

 cocytes. The variety which is of service in this study is 

 histologically described as follows: 



Polymorphonuclear or polynuclear leucocytes constitute the 

 form more frequently encountered (in normal blood), and prob- 

 ably represent the fully developed condition of the white blood- 

 cell. These elements are distinguished by the variously distorted 

 nucleus, which, being fairly rich in chromatin, presents a striking 

 figure in stained preparations. The nuclei appear imperfectly 

 separated into variously disposed segments, so that they recall the 

 letters O, S, U, V, Z, etc. The segments usually retain connec- 

 tion by delicate threads of chromatin; exceptionally these bridged 

 become broken, in which case the term polynuclear is appro- 

 priate. Occasionally cells, may be observed containing granules 

 which stain deeply with eosin. Such eosinophilic leucocytes 

 probably represent the final phase of development. 3 



PRINCIPLES INVOLVED 



Wet process. In attempting to differentiate between 

 raw and pasteurized milk, I have" shown that when certain 

 stains are put into milk and allowed to act wet, there is a 

 distinct difference in the way in which the stain acts on the 

 cells in the pasteurized milk and on the cells in the raw milk. 



When the proper amount of stain is used, the cells in the 

 raw milk are not stained at all, while the nuclei of the cells in 

 the pasteurized milk are well stained. If the stain should be 

 too concentrated, the nuclei of the cells in the raw milk may 

 be stained, but only slightly, while those in the pasteur- 

 ized milk are always deeply stained. 



The staining of the pasteurized cells and the failure to 

 stain the cells in the raw milk is to be explained on the theory 

 that the heat of pasteurization is sufficient to ".fix" (in the 

 histological sense) the protoplasm of the leucocytes and thus 

 make staining possible. 



Brief description. The method may be briefly described 

 as follows: The milk to be tested is mixed with an equal 



Pierson, Textbook of Normal Histology, sixth edition, p. 106. 

 6 Loc. cit. 



