SAVAGE’S METHOD FOR LEUCOCYTES 409 
immersion objective. The presence of cells in such a field was regarded 
by Stokes as justification for excluding an animal from a herd. 
Reed’s Method for Leucocytes in Milk. 1. Fill 10 ¢.c. centrifuge 
tubes with milk and heat for ten minutes at 70-75° C. 
2. Centrifuge the tubes at high speed for ten minutes. Remove the 
upper layers of cream and milk with a pipette and refill the tubes with 
distilled water. Centrifuge again for three or four minutes. 
3. Draw off all except 3 ¢.c. of liquid in the point of the centrifuge 
tube. Wipe out the upper part of the tube with a bit of absorbent 
cotton fastened to the end of a glass rod. Mix thoroughly the remaining 
liquid and sediment. 
4. Transfer a drop of this mixture to a clean Thoma-Zeiss blood- 
counting cell and place the cover glass over it. Count the cells under 
a one-sixth objective. If the number of leucocytes 1s low, the entire 
area of the cell should be counted, using a mechanical stage to move the 
slide. If their number is large, five or six small squares may be counted 
and averaged. The average number per small square multiplied by 
200,000 will give the number of leucocytes per cubic centimeter in the 
original milk. 
Savage’s Method for Leucocytes in Milk. (Savage, 1914.) The 
ordinary Thoma-Zeiss blood-counting chamber is employed. Direct 
counting of the cells is impossible owing to the opacity caused by the 
large amount of fat. One c.c. of the milk is accurately transferred 
to a centrifugal tube (about 15 c.c. capacity) of the usual pattern, 
and freshly filtered Toisson’s solution is poured in to almost fill the 
tube. The two fluids are well mixed and then centrifugalized for 
ten minutes. The cream is well broken up by a clean glass rod, to 
disentangle leucocytes carried to the surface, and the mixture centrifu- 
galized for an additional five minutes. All the fluid is then removed 
down to the 1 c.c. mark, great care being taken not to disturb the deposit. 
This can be conveniently and readily done by means of a fine glass tube 
connected to an exhaust pump. Theoretically, all the cellular elements 
present in the original 1 c.c. of milk are now present in the 1 ¢.c. of fluid. 
The deposit is thoroughly well mixed (with a wire), and disturbed 
through the 1 ¢.c. A sufficient quantity is placed on the ruled squares 
of the Thoma-Zeiss apparatus, and the cover glass put on. The number 
of cells is counted in a number of different fields of vision, moving reg- 
ularly from one field of vision to another. The diameter of the field of 
vision is ascertained before counting by drawing out the microscope tube 
until an exact number of sides of the squares spans a diameter of the 
field of vision. 
