EXAMINATION OF MILK 161 



More than five cells in a field are sufficient to con- 

 demn the milk. 



EXERCISE 2. STEWART'S METHOD, MODIFIED BY SLACK 



1. Fill 2 c.c. of milk into a tube provided for the 

 purpose. 



2. Centrifugalize at a speed of 2,500 to 3,000 revo- 

 lutions a minute. 



3. The stopper is then removed and the sediment 

 smeared on a slide so as to cover 4 square centimeters. 



4. Examine the slide under the oil-immersion lens 

 and count the cells and streptococci. 



More than 50 cells are sufficient to condemn the 

 milk. 



EXERCISE 3. DOANE-BUCKLEY METHOD, MODIFIED BY 

 RUSSELL AND HOFFMANN 



1. Heat sample of milk for i minute at 85 C. 



2. Centrifugalize 10 c.c. for 20 minutes. 



3. Remove cream and milk, leaving o . 5 c.c. milk. 



4. Mix and place in a blood counter. 



5. Allow to settle for 2 minutes. 



6. Count the cells in several hundred squares. 

 The average number of cells per square is multiplied 

 by 200,000 to arrive at number of cells per c.c. of milk. 



EXERCISE 4. PRESCOTT AND BREED'S METHOD 



1. Remove with capillary pipette with rubber bulb 

 one drop (o.oi c.c.) of the shaken sample of milk. 



2. Spread over i square centimeter of a glass slide. 



3. Dry by gentle heat. 



4. Dissolve out the fat with xylol. 



5. Fix smear in alcohol for a few minutes. 



6. Overstain with methylene blue. 



7. Decolorize with alcohol. 



