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 Avork has been done by State and 
city health authorities in the examination of dairy milk, Avith a AueAA" 
to determining the significance of these elements, and fixing standards 
limiting their number in acceptable dairy milk. It Avas early observed 
that m the milk of cows AAuth udder disease of an inflammatory nature, 
pus cells and streptococci AA^ere almost invariably present in large 
numbers. Following this observation, examinations Avere made to 
determine hoAV often leucocytes and streptococci were present in 
market milk. The result shoAA^ed that they AA^ere present in the 
majority of milks to a greater or less extent. They AA^ere not so 
numerous, howeAmr, as m the milk of diseased animals. The interpre- 
tation placed upon these findings — viz, that one or more of the coaa^s 
of the dairy herd from AAdiich the milk Avas derived Avas affected AAuth 
garget (an inflammation of the udder) — is no longer regarded as 
strictly correct, since it is noAA^ Avell proven that the normal milk of 
healthy coavs alAA^ays contains leucocytes and usually streptococci. 
In the last tAAm or three years Avork has been done that throAA^s a iicaa^ 
light on the subject and explains some of the discordant results pre- 
viously obtained. 
Wliether 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 AA^ere first looked upon as pus cells, it is readily understood 
why repugnance Avas felt at the idea of taking them in food, even if 
they AA^ere 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, 
a This article is reprinted without revision, owing to Doctor Miller’s death, Novem- 
ber 24, 1908. 
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