its virulence for several months in dried sputum if protected from the
light. Its vitality enables it to resist high temperatures, changes in
temperature, drying and putrefaction to a, greater degree than most
non-spore-producing germs. Direct sunlight destroys the germ within a few
hours, but it may live in poorly lighted, filthy stables for months. A
temperature of 65\260 C. destroys it in a few minutes.

Animals that, have advanced or open tuberculosis may disseminate the germ
of the disease in the discharge from the mouth, nostrils, genital organs,
in the intestinal excreta and milk. The germs discharged from the mouth and
nostrils are coughed up from the lungs and may infect the feed. Milk is a
common source of infection for calves and hogs. Allowing hogs to run after
cattle is sure to result in infection of a large percentage of them, if
there are any open cases of tuberculosis in the herd.

PREDISPOSING CAUSES.--Any condition that may lessen the resistance of the
body or enable the tubercle bacillus to survive the exposure outside the
body favors the development of the disease and the infection of the healthy
animals. Crowded, poorly ventilated, filthy stables lower the
disease-resisting power of the animal, and favor the entrance of the germs
into the body. Under such unsanitary conditions, tuberculosis spreads
quickly among dairy cattle, and a large percentage of the animals develop
the generalized form of the disease. Sanitary stables and yards do not
prevent the spread of the disease among animals that live in close contact
with one another. Fresh air and sanitary surroundings only check the spread
and retard its progress.

INTRODUCTION OF TUBERCULOSIS INTO THE HERD.--The common method of
introducing tuberculosis into the herd is through the purchase of animals
having the disease. Such animals may be in apparent good health at the time