THE DETECTION OF PASTEURIZED 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 bridges 
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.’ 
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 
5 Pierson, Textbook of Normal Histology, sixth edition, p. 106. 
® Loe. cit. , 
