493 
In this connection it may be stated that the market milk of the 
District of Columbia has recently been examined by the writer for 
the presence of tubercle bacilli by the intra-abdominal inoculation 
of guinea pigs, and in two samples, or 2.7 per cent of the 73 speci- 
mens tested, virulent tubercle bacilli were recovered. The ease with 
which tubercle bacilli may be eliminated by the udder was strikingly 
illustrated by an experiment conducted by the Royal British Com- 
mission, in which a cow injected with human tubercle bacilli under 
the skin of the shoulder began excreting tubercle bacilli from the 
mammary gland seven days later, and continued to do so until its death 
from generalized tuberculosis thirty days after inoculation. It has 
been shown by Gaffky and Eber in Germany and Schroeder in this 
country that, even when the tubercle bacilli are not being excreted 
by the udder, the dust and manure of the stable where the diseased 
animals are kept are in many cases contaminated with tubercle 
bacilli. This contaminated material may readily infect the milk 
during the process of milking, even though the milk comes from a 
healthy cow. The importance of this method of infecting milk can 
not be too greatly emphasized, when it is known that cattle in prime 
condition without any udder lesions and with but slight alterations 
in the lungs frequently raise tuberculous mucus into the pharynx 
while coughing, then swallow this material, and thus contaminate 
the feces. In a recent examination at the Bureau of Animal Industry 
Experiment Station of the manure passed by 12 cow t s just purchased 
from dairy farms in this city and affected with tuberculosis to an 
extent only demonstrable by the tuberculin test, tubercle bacilli were 
found in over 41 per cent of the cases, both by microscopic examina- 
tion and animal inoculations. The danger from this method of 
infecting milk is impressed upon us as consumers when we realize 
that on an average probably 25 per cent of all the cows which sup- 
ply milk to the District are tuberculous, judging from the results of 
recent tuberculin tests. Thus far these tests have all been volun- 
tary on the part of the dairymen, but it is pleasing to note the large 
number who have had their herds cleaned of tuberculosis and the 
premises disinfected. Our records on December 1, 1907, show that 
during the past six or seven months the Bureau has supervised the 
testing of 1,538 cattle in 104 herds supplying milk to Washington, 
with the result that 260, or 16.9 per cent, were found tuberculous. 
Many other tests have been made by local veterinarians, of which 
we have no records. The latter per cent is scarcely a fair estimate 
of the extent of tuberculosis in the dairy herds of this vicinity, since 
our tests include many herds which have either been cleaned pre- 
viously by private tests or which have such a healthy appearance as 
to remove all suspicions of tuberculosis on a physical examination. 
