CELLULAR ELEMENTS OF MILK 613 



thus Ayers has shown that an exposure of thirty minutes at a tem- 

 perature of 145 C. fails to kill all colon bacilli. 1 The bacteria which 

 survive pasteurization at this temperature are chiefly acid formers. 2 



Cellular Elements of Milk. It has long been known that milk 

 drawn from healthy cows contains variable numbers of cellular ele- 

 ments; these elements have been variously referred to as leukocytes, 

 milk leukocytes, pus cells or gland cells. They may be either mono- 

 nuclear or polymorphonuclear, and there is little unanimity in inter- 

 preting their significance. Harris 3 believes they have little sanitary 

 significance as a general rule. Attempts have been made to correlate 

 the numbers of cellular elements in milk with the leukocyte and eryth- 

 rocyte count of the blood of the homologous animal, but without 

 avail. 4 



It is a fact, however, that an inflammation of the udder of the cow 

 is frequently associated with an unusually large number of cells in 

 the milk, indistinguishable from polymorphonuclear leukocytes, and 

 at times these cells are phagocytic. The increase in cellular content 

 may be definitely restricted to one quarter of the udder. 



An examination of the milk freshly drawn from 168 normal cows 

 was made quantitatively for cellular elements and over 80 per cent, 

 of the animals (composite sample from four quarters of the udder) 

 showed less than 400,000 cells per cubic centimeter of milk. The 

 period of lactation appeared to exercise little influence upon the 

 cellular content, provided the samples were collected at least two 

 weeks after parturition. 5 



1 Jour. Agr. Res., 1915, iii, No. 5. 



2 Ayers and Johnson, Bull. 126, Bureau Animal Industry, 1910; ibid, Bull. 161, 1913. 



3 Jour. Inf. Dis., 1907, Supp. Ill, p. 50. 



4 At present comparatively little attention is directed to the cellular content of milk, 

 and inasmuch as it is usually impossible to trace the milk to its source after it is bottled 

 in the city, the method is not of much practical importance. A careful histological 

 study of the cellular elements of milk by a competent cytologist might reasonably be 

 expected to throw at least some light upon the origin and significance of milk leukocytes. 



5 Kendall, Collected Studies from the Research Laboratory, New York City, iii, 169. 



