lk of tuberculous cows in
which there were no indications of udder disease do not bear out this
theory, since tubercle bacilli have been found in their milk. Some
authorities still believe that the udder is diseased when the milk is
infected, but that the disease escapes observation. However this may be,
the fact that the udder may be diseased and the disease not recognizable
simply casts suspicion upon all milk from tuberculous animals. We know that
the milk of tuberculous cattle may or may not contain tubercle bacilli when
the udder is apparently free from disease, but we have no rapid method of
determining whether in any given case the milk contains tubercle bacilli or
not. Moreover, the bacilli may be absent at one time and present at another
in milk from the same cow. When we consider, therefore, the extent of
tuberculosis and the hidden character of the disease, a certain degree of
suspicion rests upon all milk from untested cattle. Fortunately, tubercle
bacilli are readily destroyed by the temperature of boiling water, and
hence both meat and milk are made safe, the former by the various processes
of cooking, the latter by boiling for a few moments. It is incumbent upon
all communities to have dairy cows examined and tested with tuberculin. If
disease is detected, the affected animal should be killed at once or else
all opportunity for the sale of such milk removed by appropriate measures.
Where milk or cream is sold to the trade in large towns or cities
pasteurization should be required as an additional safeguard.

Recently there has been much discussion of the question as to whether human
and animal tuberculosis are identical diseases and as to the possibility of
the tuberculosis of animals being transmitted to man or that of man being
transmitted to animals.

The fact that tuberculous material from human subjects often failed to
produce serious disease in cattle was observed by a number of the earlier
investigators who experimented with such virus. It was the experiments and
comparative studies of Theobald Smith, however, which attracted special
attention to the difference in virulence shown by tubercle bacilli from
human and bovine sources when inoculated upon cattle. Smith mentioned also
certain morphological and cultural differences in bacilli from these two
sources, and in the location and histology of the lesions in cattle
produced by such bacilli. He did not conclude, however, that bovine bacilli
could n