THE FREQUENCY OF TUBERCLE BACILLI IN THE MARKET 
MILK OF THE CITY OF WASHINGTON, D. C. 
By John F. Anderson, 
Passed Assistant Surgeon and Assistant Director Hygienic Laboratory, Public 
Health and Marine-Hospital Service, Washington, D. C. 
INTRODUCTION. 
Numerous investigators in recent years have shown the infectious- 
ness of milk containing tubercle bacilli for animals. Whether the 
milk from animals with tuberculosis but with healthy udders con- 
tains tubercle bacilli is not definitely settled. Many prominent scien- 
tists seem to have shown that at times the milk from such animals 
does contain tubercle bacilli virulent for laboratory animals, but in 
the view of recent work there may be some doubt as to whether the 
bacilli really passed through the udder but gained access to the milk 
from contamination with feces containing tubercle bacilli. 
Schroeder and Cotton a have recently shown that cows so slightly 
affected with tuberculosis as only td be discoverable by the tuberculin 
reaction pass virulent bacilli in their feces. Many believe that milk 
from a tuberculous coat with unaffected udder is free from infection 
and becomes infected from the feces of the animal or its environment. 
This observation is of the yery greatest importance, and if confirmed 
shows, more than ever, that the greatest care is necessary in guarding 
milk from contamination from the time it is drawn until it is con- 
sumed. 
The milk supply of many of the cities of Europe and England has 
been examined for tubercle bacilli. Most observers have used the 
animal test; they have injected various amounts, either centrifugal- 
ized or not, into guinea pigs or rabbits. The percentage of samples 
showing tubercle bacilli has varied between very wide limits, no 
doubt dependent upon the difference in the number of tuberculous 
cows in the herds supplying milk to the different cities and on dif- 
a Schroeder, C. C. and Cotton, W. E. : Bull, of the Bureau of Animal Industry, 
1907. 
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