464 MILK 



standard was raised to ten by Bergey. The method is evidently 

 inaccurate. 



Slack's modification of the method is used in many labora- 

 tories. The milk is placed in small tubes, each end of which is 

 closed with a rubber stopper. The tubes are then centrifuged, 

 and the sediment and cream both of which adhere to the rubber 

 stoppers are spread on a slide, stained, and examined micro- 

 scopically. 



An improved method was proposed by Doane and Buckley. 

 It was modified by Russell and Hoffmann, who found that cell- 

 ular elements are precipitated with greater ease and that a larger 

 count is obtained from heated milk than from raw milk. The 

 method is carried out as follows: The sample of milk is heated 

 to 85 C. for one minute. Ten c.c. of the heated sample are then 

 whirled in a centrifuge at a speed of about 2000 revolutions per 

 minute for twenty minutes. The cream is removed with a cotton 

 swab. The supernatant milk is removed with a pipet, leaving 

 0.5 c.c. of milk. Two drops of a saturated alcoholic solution of 

 methylene-blue are added to the sediment, and then the tube is 

 kept in boiling water for two or three minutes. Enough water 

 is added to bring the volume to 1 c.c. A Thoma-Zeiss blood 

 counter is used for counting the cells. The cells should be counted 

 in several hundred squares to obtain accurate results. The aver- 

 age number of cells counted per square is multiplied by 200,000 

 to arrive at the number per cubic centimeter of milk. 



Trommsdorff proposed a method radically different from the 

 foregoing ones. This method calls for special tubes which are 

 drawn out to capillary points. They are graduated from 0.001 

 to 0.02 c.c. Ten c.c. of milk are whirled for a few minutes at a 

 speed of 1500 to 2000 revolutions per minute and the amount 

 of sediment read in the graduated capillary tube. If the sedi- 

 ment is yellow or pink, there is reason for suspicion. The sedi- 

 ment may be large on account of dirt in the milk and, conse- 

 quently, the test is not always reliable. 



The latest and most accurate method is the one devised by 

 Prescott and Breed. The sample is well shaken and 0.01 c.c. 

 removed with a specially constructed pipet with a rubber bulb. 

 The amount is spread evenly over 1 sq. cm. of an ordinary slide. 

 The smear is dried by gentle heat, the fat dissolved out with 

 xylol, and the slide then immersed in alcohol for a few minutes 

 for fixation. The slide is then dried and overstained with meth- 

 ylene-blue and decolorized with alcohol. The cells show up clearly 

 in a blue field, the background consisting of the dried plasma 

 solids. Smears should be made in duplicate, as it is sometimes 

 difficult to obtain an even spread. The diameter of the field is 



