CONCENTRATION OF CELLULAR ELEMENTS 175 



taken from the entire milking of the animal, as the strippings 

 contain a somewhat larger number of cells than other portions 

 of the milk. For the purpose of examination take 200 c.cms. 

 in a stoppered bottle. 



Time Interval between Collection and Analysis. To secure 

 satisfactory results, milk must be examined in a sweet condi- 

 tion. Development of acidity tends to precipitate casein 

 in the milk and thus obscure the examination of microscopic 

 preparations. Samples received from a distance can be pre- 

 served for satisfactory microscopical examination by the 

 addition of formaUn at the time of collection — a proportion of 

 1 c.cm. to 250 c.cms. of milk. Formalin has been foimd the 

 best preservative to use although it causes contraction of the 

 cells to some extent. 



Pbgcedtjbe with Reference to Peepaeation of Sample 



1. Heating Sample. To secure the complete sedimentation 

 of the cellular elements in the milk, it is necessary to heat the 

 same to a temperature which will break down the fat globule 

 clusters, or lessen the ordinary creaming properties of the milk. 

 Samples should be heated at 65° to 70° C. for not less than ten 

 minutes, or from 80° to 85° where very short periods of exposure 

 (one minute) are given. This treatment causes the more homo- 

 geneous distribution of the fat globules through the milk, and 

 when the sample is then subjected to centrifugal force, the 

 cell elements are not caught in the rising fat globules, but on 

 accoimt of their higher specific gravity are concentrated in the 

 sediment by centrifugal force. 



2. Concentration of Cellular Elements. After centrifugaK- 

 sation the cream and the supernatant milk are removed, with 

 the exception of the last f c.cm., by aspirating with an exhaust 

 pump and wiping the walls of the tube with a cotton swab. 

 After thoroughly mixing the sediment with a glass rod, enough 

 of the emulsion is placed in an ordinary blood coimter (Thoma- 

 Zeiss pattern) to fill exactly the cell. The preparation is then 

 allowed to stand for a minute or two to permit the cellular 



