MICROSCOPIC STUDY OF MILK. 285 



ment to make a uniform emulsion, and then, with a pipette, 

 the emulsion, including the sediment, is withdrawn from the 

 vials and distributed uniformly on the surface of two ordi- 

 nary sized covered glasses. These are allowed to dry in the 

 air, after which they are fixed in a flame by the ordinary 

 method for microscopic study of bacteria. The cover-glasses 

 are then placed in a covered dish with chloroform or ether, 

 for the purpose of dissolving the fat, after which they are 

 stained for the detecting of pus cells. The stain most satis- 

 factory to use is methylene blue, a solution of which is 

 allowed to act on the cover-glass for a few minutes ; it is then 

 washed away and the specimen studied under the micro- 

 scope. This method of staining will color bacteria a deep 

 blue and will also stain the pus- cells. The latter appear as 

 large, irregularly shaped, deeply stained cells as shown in 

 Fig. 9, page 34. It is difficult to distinguish pus cells from 

 the ordinary leucocyte cells which are quite sure to be in the 

 milk. Nearly all samples of milk show some such cells. If 

 the cells are very numerous they indicate the presence of pus. 

 The common method of study is to count the number of such 

 cells in twenty microscopic fields with a one-twelfth-inch 

 objective. If the average number in a field is over twenty it 

 is quite certain that it indicates the presence of pus, and, 

 therefore, suggests some inflammatory condition in the udder ; 

 a smaller number of cells per field than this cannot be re- 

 garded as necessarily indicating the presence of pus. 



To detect the presence of tuberculosis bacteria is not 

 easy, nor are the results certain. For this purpose the sedi- 

 ment prepared as above described, and also some cover- 

 glasses made from the cream in the same way, should be 

 stained by the ordinary stains for tuberculosis bacteria. The 

 directions for such staining can be found in text-books of 

 laboratory bacteriological technique and the details need not 

 be given here. The presence of bacilli which are stained by 

 the methods employed do not certainly indicate the presence 



