158 UNIVERSITY OF WISCONSIN STUDIES 
essary for the pasteurization of milk, namely, at from 60 to 63°C, 
(140-145°F.) 7 
INTERPRETATION OF RESULTS 
Illustrations: The results of this method of staining are 
shown in Plates I and II, Figures 1 to 26. These drawings 
are all made under an oil immersion lens and by means of 
the camera lucida. 
Figures 1 to 4 show cells in the raw milk. Here the back- 
ground is stained, while the cells remain clear or unstained. 
In Fig. 5 the milk was heated to 58° C. (137° F.) for 20 
minutes and in Fig. 6 to 60° Co. (140° F.). Here the poly- 
morphonuclear leucocytes have their nuclei lightly stained. 
Figures 7, 8, and 9 show the cells in milk that has been 
pasteurized at 63° C. (145° F.) for 20 minutes. The nuclei 
are all deeply stained and the segments well rounded off and 
the fragments discrete. Fig. 10 shows cells from milk heated 
to 65° C. (150° F.), and Fig. 11 shows cells from milk 
heated to 70° C. (158° F.). Figures 10 and 12 show the 
bacteria well stained. 
Figures 13 to 18 represent groups of leucocytes selected 
from various fields to show variations in form, size, and 
staining reaction at the various temperatures indicated. Ex- 
eept for the raw milk, no attempt has been made to represent 
the background. 
Figures 19 and 20 are the results obtained by applying a 
counter stain to the preparations obtained by the staining 
with methylene blue in the usual way. The advantage of the 
counter stain is that it brings out or differentiates the leu- 
cocytes in the raw milk. (The preparations are made in the 
usual way and when the smears are dry, they are immersed 
for a few seconds in a 1 per cent solution of orange G in 
aleohol (95 per cent) and examined after drying without 
washing. ) 
Figures 21 and 22 are from preparations made by a method 
suggested by Traum.® Jn this method the cells are separated 
‘ Loc. cit. 
®J. Traum, Laboratory Methods to Improve Milk in Amer. Jour, Vet. 
Med, 10, 717, 1915. 
