494 
intervals, favorable conditions for the migration of leucocytes are 
found. 
It was deemed advisable by the early students of the subject, who con- 
sidered all leucocytes in milk as “ pus cells” and evidence of inflamma- 
tion of the udder, to fix a limit to the number which might be allowed 
in a market milk. Stokes (loc. cit.) regarded an average of 5 cells to 
the field of the microscope, using his counting method, as indicative of 
pus. Bergey® adopted 10 cells per field as a standard. Stewart 
(loc. cit.) regarded 23 cells per field and Slack (loc. cit.) 50 cells as a 
proper standard, all using a modification of Stewarts technique.. 
Doane advocates 500,000 leucocytes per cubic centimeter, Tromms- 
dorff 10 volumes of sediment to 10,000 volumes of milk as a safe 
limit. Stewart’s is the standard commonly employed in municipal 
health laboratories and corresponds roughly to 100,000 leucocytes per 
cubic centimeter. All of the above standards are arbitrary and are 
founded solely upon individual experience. The standard suggested by 
Trommsdorff limiting the amount of sediment in a centrifuged sample 
of milk seems valuable, not so much as an enumeration of the leuco- 
cytes as an indication of objectionable solid matter in suspension. It 
is of interest to note that although the number of leucocytes in milk 
from cows with diseased udders is usually much increased, Bussell 
and Hoffmann have shown that this is not necessarily true, in some 
instances the count running below the average for normal milk. The 
daily variation in such cases often brings the count well within the 
usual normal limits. It seems likely that a numerical standard for 
leucocytes sufficiently high to include the milk of the greater majority 
of healthly cows would not be low enough to exclude in some cases the 
milk of cows with disease of the udder. Other and more definite signs 
of inflammation than that furnished by the leucocyte count alone 
must be sought. 
Doane (loc. cit.) states that the occurrence of fibrin is positive proof 
of the existence of inflammation and has devised ways of demon- 
strating its presence in milk. The matter requires further study. 
The leucocytes per se can not be regarded as deleterious or foreign 
ingredients of milk; it is scarcely reasonable to expect that a 
food so distinctly animal in its origin should contain no organized 
elements. 
The significance of pus in milk has been studied principally in 
connection with micro-organisms, looked upon as the exciting cause 
of the mastitis, with which the pus is associated. In the stained 
smears of milk sediment examined by the earlier investigators of 
leucocytes in cow’s milk, attention was drawn to the large number 
of chain-forming micro-organisms (streptococci) present. They were 
°Bull. No. 125, Penna. Dept. Agric., 1904. 
