194 MILK AND THE PUBLIC HEALTH chap. 



cotton swab as far as possible. The tube is centrifuged for one 

 minute more and the cream again removed. Without disturb- 

 ing the sediment, the overlying milk is syphoned off, leaving 

 fluid to the depth of ^ inch above the sediment. Two drops 

 of a saturated alcoholic solution of methylene blue are 

 added, thoroughly mixed with the sediment by shaking, and 

 set aside in boiling water for 2 or 3 minutes to allow the 

 leucocytes to take up the stain. The tube is then filled up to 

 1 c.c. with water, the contents shaken thoroughly, and a little 

 transferred to a blood -counting chamber. The number of 

 leucocytes in all, or a definite number of the squares, is 

 ascertained, and the number per c.c. of milk deduced. 



Modifications of these methods have been introduced. 

 Eussell and Hoffmann, using the Doane-Buckley method, found 

 that by heating the milk to 60°— 70° C. before centrifugalisa- 

 tion, a very great increase almost always results in the 

 number of cells. They ascribe this to the entangling effect of 

 the fat, an effect which is broken down by heating. They 

 suggest that the milk should be subjected to a preliminary 

 heating. "A momentary exposure at 70° C. or above, or a 

 more prolonged heating for a few minutes at 60° C, will so 

 alter the physical arrangement of the fat globules in milk, 

 that practically all the cellular elements may be recovered." 



Hewlett, Villar, and Revis find that the addition of form- 

 aldehyde (6 drops of formalin to 60—70 c.c. of milk) has a 

 similar effect. They ascribe this increase to the formalin 

 breaking down aggregations of cells, and causing them to be 

 more evenly distributed. 



B. The Examination of the Stained Centbifugalised 



Deposit 



To obtain comparable results the sediment from a definite 

 amount of milk should be examined after centrifugalisation 

 for a definite period. Ten c.c. of milk centrifugalised for 10 

 minutes is convenient. Part of the deposit is spread thinly 

 but uniformly over a cover-slip, dried in air, fixed in the 

 flame, or preferably by soaking in a mixture of equal parts 

 alcohol and ether for one minute, stained by methylene blue 

 and mounted in balsam. 



