of purchase, and be affected with generalized or open tuberculosis.

_A source of infection_ is by unknowingly buying cows that have reacted to
the tuberculin test. The indiscriminate use and sale of tuberculin are
largely responsible for the large number of reacting animals that have been
placed on the open market. This dishonest practice has resulted in the
rapid spread of the disease in certain localities. For years a large
percentage of the breeding herds have been infected, and the writer has met
with several herds of dairy and beef cattle that became tubercular through
the purchase of tubercular breeding animals.

SYMPTOMS.--There is no one symptom by which we may recognize tuberculosis
in cattle and hogs. None of the symptoms shown by a tubercular animal are
characteristic, unless it is in the late stage of the disease. In a
well-cared-for animal, the lymphatic glands in the different regions of the
body, the lungs, liver and other organs, may be full of tubercles without
causing noticeable symptoms of disease (Fig. 89).

[Illustration: FIG. 89.--A tubercular cow. This cow was, to all
appearances, in good health, but showed generalized tuberculosis on
post-mortem examination.]

_Tuberculosis may attack any organ of the body_, and in the different cases
of the disease the symptoms may vary. Enlargement of the glands in the
region of the throat, and noisy, difficult breathing are sometimes present.
The udder frequently shows hard lumps scattered through the gland. Bloating
may occur if a diseased gland in the chest cavity presses on the oesophagus
and prevents the usual passage of gas from the paunch. Chronic diarrhoea
may occur. If the disease involves the digestive tract, the animal is
unthrifty and loses flesh rapidly. Coughing is not a characteristic