MILK HYGIENE 



119 



With the rod a drop of thoroughly mixed milk and sedi- 

 ment is transferred to the cell and the cover placed in position. 

 The transfer should be made at once after mixing, and the 

 drop should be just large enough to fill the cell completely, 

 or at least three fourths of it, but should not overflow into 

 the moat. The preparation should be allowed to stand a 



FIG. 18. THOMA-ZEISS BLOOD-CORPUSCLE-COUNTING CELL 



A, plain glass cover; /?, glass with circular hole in its center; C, glass bear- 

 ing ruled area. The distance from the upper surface of C to the lower surface 

 of A is 0.1 mm. 



moment after filling and covering, to allow the fat globules 

 to rise to the upper portion of the cell and the leucocytes 

 to settle. 



The counting is done with a -inch objective of long work- 

 ing distance (0.66 numerical aperture), counting the number 

 of leucocytes in the entire ruled area in milks low in con- 

 tent. With increased content a less number of squares may 

 be counted. The small squares will be found divided by double 

 lines into sets of sixteen, in order to facilitate the counting. 

 At least six of these sets should be counted. The average 

 number of leucocytes per small square multiplied by 200,000 



