176 Report of the Department of Bacteriology of the 



has been found. It is clear that there is an increase in the 

 number of cells in the strippings which may possibly be due to 

 manipulation of the udder as suggested by other investigators. 

 However, it is equally possible that this increase may be due to 

 other factors. 



The four quarters of the udder are practically independent of 

 each other, so far as the discharge of the cells is concerned, indi- 

 cating that the principal cause of the discharge of the cells is some- 

 thing which affects the quarters separately rather than the udder 

 as a whole. 



Out of the 122 individual cows whose milk has been examined, 

 59 have been found to give cell counts under 500,000 per cubic 

 centimeter, 36 gave counts between 500,000 and 1,000,000 per cubic 

 centimeter, and 27 gave counts over 1,000,000 per cubic centimeter. 

 The average cell counts for all of these cows was 868,000 cells per 

 cubic centimeter. The milk of all of these cows was normal in 

 appearance and was sold or used by their owners, who had every 

 reason to suppose that the milk was normal milk. 



Changes of a considerable amount in the 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 the type of machines here used 

 is somewhat less than that of hand-drawn milk. The fact that all 

 of the cows in the Station herd have been milked by machine during 

 part, at least, of their lifetime is the only apparent explanation of the 

 fact that the milk of this herd showed a much lower average cell 

 content than the milk of other herds. The results obtained in the 

 course of the experiments show clearly that there is no reason for 

 any fear that high vacuums or changes in the vacuum may of them- 

 selves cause the excessive discharge of cells or draw blood from the 

 interior of the udder. 



The reasons for the discharge of the two kinds of cellular elements 

 are undoubtedly entirely different. The epithelial cells are presum- 

 ably discharged because they are worn out in the process of the 

 secretion of the milk. Pathological changes in the udder tissues 

 may also cause their discharge from the udder, but under normal 

 conditions, their presence in the milk is probably correlated solely 

 with the processes of secretion. 



