118 Report of the Department of Bacteriology of the 



cells discharged and specific bacterial infections of the udder. 

 Such being the case, it is impossible to decide whether or not 

 the discharge of large numbers of cells or of specific kinds of cells 

 in connection with streptococci or other bacteria has any sanitary 

 significance. 



6. Considerable changes in the amount of vacuum used to operate 

 cow milkers were found to be entirely without effect on the cell 

 content of the milk. Several things seem to indicate that the number 

 of cells present in milk drawn by a machine operated by the use 

 of a vacuum is somewhat less than the number present in hand- 

 drawn milk. The results obtained show that there is no reason 

 for thinking that changes in the vacuum or that high vacuums 

 may in themselves cause the discharge of excessive numbers of 

 cells or that high vacuums may draw blood from the interior of 

 the udder. 



7. The method of preparing dried milk smears here used has 

 been found to give excellent results. It is a comparatively simple 

 method to use and has the added advantage that the smears so 

 prepared can be used for counting the bacteria present as well 

 as the cells. The conclusion formulated in earlier papers, that 

 none of the results obtained by previous investigators who have 

 determined the number of cells by counting them in centrifuge 

 sediments are accurate enough to be of value other than to show 

 general conditions, has been entirely substantiated in the present 

 investigation. 



INTRODUCTION. 



Normal milk is a secretion which shows large numbers of small 

 fat drops in it when viewed under the microscope. Among these 

 fat drops there may be seen certain cells derived from the udder 

 of the cow. The exact nature of these cells is still disputed by some 

 but there can be little doubt that the majority of them are leuco- 

 cytes (white blood corpuscles) which have made their way into the 

 milk from the lymph or blood of the cow. Others of these cells, 

 less in number, are epithelial in nature; that is, they are worn-out 

 secreting cells of the udder itself. 



The number of these cells in milk is discussed at length in a paper 

 by Breed and Stidger 1 where the following conclusion is reached: 



1 Breed, R. S., and Stidger, I. R. The number of cellular elements in milk. Jour. 

 Inf. Dis., 8 : 361-385, 1911. 



