MILK IN ITS RELATION TO THE PUBLIC HEALTH CM 
possible. Ordinary market milk is produced under less rigorous 
conditions anrl the bacterial content is usually nuich greater; from 
lOO.OOO to :)()(),()()() bacteria per cubic centimeter, or even 1,()()(),()00 
bacteria represent the usual standards enforced. 
Pasteurization of milk is rapidly becoming obligatory in many 
cities, particularly for the ordinary grades of milk. Pasteurizaticm is 
carried out by heating milk to about 145° F. (the degree of heat 
\aries in different places), and maintaining it at that temperature for 
thirty minutes. This degree and duration of heat is deemed sufficient 
to weaken or destroy pathogenic organisms without altering the 
nutritive value. The ideal method of pasteurization is to heat the 
milk to the required temperature for the required time in the bottle 
which goes to the consumer, thus entirely eliminating the danger of 
human contamination subsequent to the process. 
The pasteurizing process does not kill many of the milk bacteria; 
thus Ayers has shown that an exposure of thirty minutes at a tem- 
perature of 145° C. fails to kill all colon bacilli.^ The bacteria which 
survive pasteurization at this temperature are chiefly acid formers.'- 
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 \'ariously referred to as leukocytes, 
milk leukocytes, pus cells or gland cells. They may be either mono- 
nuclear or polymorphonuclear, and there is little imanimity in inter- 
preting their significance. Harris'' 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.* 
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 chiefly restricted to one quarter of the udder. 
An examination of the milk freshly drawn from IGS 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.^ 
' Jour. Agr. Res., 1915, 3. No. 5. 
• Ayers and .Johnson: Bull. 126, Bureau Animal Industry, 1910; ibid., Bull. 161, 191.3. 
3 Jour. Infec. Dis., 1907, Supp. Ill, p. 50. 
'' 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 ot the cellular elements of milk by a competent oytologist might reasonablj' be 
expected to throw at least some light upon the origin and significance of milk leukocytes. 
^ Kendall: Collected Studies from the Research Laboratory, New York City, 1907, 
3, 169. 
