174 CELLS, DIRT AND DEBRIS 



the large mononuclears. The nucleus shows varieties of transi- 

 tion between the indented mononuclear and the irregular poly- 

 morphonuclear cell. As a rule, it is indented, crescrentic in 

 shape, and not possessing the multiplication so characteristic 

 of the polymorphonuclear leucocytes. 



Degenerated cells of various kinds may also be present in 

 milk. Cells may, under various influences, become partially 

 or wholly disintegrated and the contents dispersed in fragments. 

 The nucleus may split up and the chromatin spread through the 

 plasma as dust or flakes. These flakes are often designated as 

 " Nissen's Globules " and present the appearance of a darkly 

 stained centre, with or without a lightly stained border. The 

 albuminophores of Bab and Shulz which they describe as lym- 

 phocytes (15 to 20 m), containing fat and one to four proteid 

 bodies, are regarded by Ernst as degenerated fat containing 

 cells which have been attacked by macrocytes and then further 

 degenerated until the nucleus is no longer visible. 



Estimation of Cells. The first attempt to estimate the 

 number of cells in milk was that of Stokes and Wegefarth in 

 1897 ^ and consisted in the examination under an oil immersion 

 lens of a stained film prepared from the sedimeht obtained by 

 centrifugal action. This method was adopted with but slight 

 modifications by Bergey, Stewart and Slack. 



Doane and Buckley in 1905 ^ devised what is known as 

 the " volumetric method " in which a counting cell, such as is 

 conunonly used in the estimation of cells in blood, was used for 

 the enumeration of the cells in the centrifugalised deposit from 

 10 c.cms. of milk. Russell and Hoffmann^ compared the 

 " smeared sediment " and " volumetric " methods and found 

 an average variation of 112 per cent in the former as against 

 only 6 per cent in the latter. They found also '' that a pre- 

 liminary heating of the milk to 70° C. produced higher and more 

 consistent results. The details of this method, as adopted by 

 the Committee on Standard Methods of Bacterial Milk Analysis 

 of the American Public Health Association ^ are as follows : 



Collection of Samples. Samples for analysis should be 



