THE SIGNIFICANCE OF LEUCOCYTES AND STREPTOCOCCI 
IN MILK. 

By William Whitfield Miller, 
Assistant Surgeon , Public Health and Marine-Hospital Service. 
In the search for better and simpler methods for detecting milk 
from diseased cows, especially when mixed with the milk from healthy 
cows, as may be the case in market milk, particular attention has 
been paid to the presence of leucocytes and streptococci. In America, 
and to some extent abroad, much work has been done by State and 
city health authorities in the examination of dairy milk, with a view 
to determining the significance of these elements, and fixing standards 
limiting their number in acceptable dairy milk. It was early observed 
that in the milk of cows with udder' disease of an inflammatory nature , 
i|# TO.* wk ■ ~ . ' 
pus cells and streptococci were almost invariably present in large 
numbers. Following this observation, examinations were made to 
determine how often leucocytes and streptococci were present in 
market milk. The result showed that they were present in the 
majority of milks to a greater or less extent. They were not so 
numerous, however, as in the milk of diseased annuals. The interpre- 
tation placed upon these findings — viz, that one or more of the cows 
of the dairy herd from which the milk was derived was affected with 
garget (an inflammation of the udder) — is no longer regarded as 
strictly correct, since it is now well proven that the normal milk of 
healthy cows always contains leucocytes and usually streptococci. 
In the last two or three years work has been done that throws a new 
light on the subject and explains some of the discordant results pre- 
viously obtained. 
Whether the polymorpho-nuclear cells found in all milk shall be 
regarded as leucocytes or pus cells has been a subject of much dispute. 
As they were first looked upon as pus cells, it is readily understood 
why repugnance was felt at the idea of taking them in food, even if 
they were harmless. The earlier observers detected these cells in a 
large number of specimens of milk, but not in all, and concluded that 
they indicated some degree of inflammation of the udder. They 
fixed an arbitrary number (to a certain quantity of milk) as a limit, 
( 479 ) 
