282 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
per is removed, and the sediment spread on a glass slide 
by rubbing the stopper over an area of 1 square centi- 
metre. The preparation is dried in the air, stained 2 
minutes with Jenner’s blood stain and examined under 
the microscope with the 1/12 oil-immersion objective and 
a No. 8 ocular. The leucocytes in 10 fields are counted. 
An average of 23 cells to the field is the limit for normal 
milk. If the average number of cells to the field is mul- 
tiplied by 4400 the approximate number of cells per c.c. 
is obtained. 
Doane-Buckley Method.—10 c.c. of milk is centrifu- 
galized for 10 minutes in a graduated sediment tube, after 
which the cream and separated milk is drawn off with a 
pipette down to the 1 c.c. mark. A drop of saturated al- 
coholic solution of methylene blue is mixed with the re- 
maining portion and the mixture is allowed to stand one 
minute to stain the cells. One drop of this mixture is 
placed in a Thoma-Zeiss blood-counting apparatus and 
the number of leucocytes per c.c. determined. The limit 
for normal milk is 500,000 per c.c. 
Trommsdorff Test.—For this test a special sediment 
tube is used which is drawn out at the lower end into a 
small capillary tube with twenty graduations, each grad- 
uation representing 0.01 per cent. 10 cc. of milk is 
placed in the tube and centrifugalized for 10 minutes. 
The volume and color of the sediment in the capillary 
tube are then noted. The limit for sediment in milk from 
individual cows in normal condition is 0.1 per cent. and 
the color should be white or grayish white. If the sedi- 
ment exceeds this amount and is of a yellowish-color, the 
presence of mastitis secretion is indicated and the sedi- 
ment should then be examined microscopically to deter- 
mine whether it consists largely of leucocytes or of débris 
