MILK HYGIENE 121 



After centrifugalization the stopper at the cream end is 

 removed and the layer of cream disturbed with a needle, the 

 milk and cream poured out, and, without placing the tube 

 right side up, the lower stopper with the adhering sediment 

 is removed. The sediment is smeared over a definite area, 

 4 sq. cm. on an ordinary glass slide, by use of the stopper. 

 The smear should be as uniform in distribution as possible. 

 The use of a drop of water will aid in this respect. The smear 

 is allowed to air dry, and is then stained with methylene blue 

 for a few moments. The stain is carefully washed off so as 

 not to loosen the smear, and the slide allowed to dry. 



It is examined with an oil-immersion lens, placing the oil 

 directly on the dry smear. The average number of leucocytes 

 per field is determined by counting a number of fields. The 

 number that must be counted depends upon the evenness of 

 distribution of -the sediment. At least fifty should be ex- 

 amined. The diameter of the field of the oil-immersion lens 

 is determined with a stage micrometer. The number of mi- 

 croscopic fields in the total area of the smear is calculated, 

 and from the data thus obtained the average number of leu- 

 cocytes per cubic centimeter of the milk examined is deter- 

 mined. The student should prepare preparations of blood, 

 staining them with methylene blue, so as to become familiar 

 with the appearance of the white corpuscles when stained. 

 The blood is obtained as previously described. A drop of blood 

 is placed on a clean slide and spread by means of another 

 slide whose corners at one end have been chipped off. This is 

 brought in contact with the drop of blood and drawn along 

 the slide, holding the spreader at an angle of 45. A thin 

 film of blood is thus deposited along the slide, the broken 

 corners preventing the film extending to the edges of the 

 slide. 



