160 UNIVERSITY OF WISCONSIN STUDIES 
Frequently there is a tinge of blue to them so that there is 
just a suggestion of the nuclear structure of the cell visible. 
A few cells even in perfectly fresh milk may have their nuclei 
stained but less densely and compactly than in pasteurized 
milk. In the pasteurized milk, on the other hand, the nuclei 
are definitely stained, usually dark blue, while the background 
is lighter. The difference is striking and perfectly charac- 
teristic. 
Outline of leucocytes.—The outline of the cells in raw 
milk is irregular. This is probably due to protrusions or 
pseudopodia although certain authors have hesitated to accept 
these eells as leucocytes because they do not show evidence of 
aineboid movement. The irregular outlines, as shown in the 
figures of raw milk, are noticeable, however, especially in 
Figures 4 and 13. 
In the heated milk the outline of the cells usually appears 
more regular. Under the influence of heat the cells have 
rounded up. There is no constant difference between these 
cells under the two conditions, however, and some observers 
have even regarded the heated cells as the more irregular. 
The irregularity of the heated cells may, however, be due to 
quite a different cause, namely, shrinkage. 
Nuclear fragments.—Only the polymorphonueleated cells 
are of value in this test. In a raw cell it is usual for the nu- 
cleus to be single but variously shaped (or polymorpho), while 
in the heated milks there is a pronounced tendeney for the 
nuclei to become separated and thus the eclls become poly- 
nucleated. The nucleus or its fragments are much more 
compact and demarkated in the heated than in the raw samples. 
Size of the leucocytes.—<As already pointed out, the heat 
of pasteurization not only affects the staining reaction of 
the leucocytes but it produces a profound change in their size. 
In raw milk these cells are frequently 10 or 12 microns in 
diameter and nearly always above 7.5 microns. In properly 
pasteurized inilks they are very much smaller, usually less 
than 7.5 microns. 
This marked reduction in size is no doubt duc to the heat 
of pasteurization which shrinks the cells. The decrease in 
size is a progressive one, depending upon the amount of heat 
