experiments were made. These resulted in practical methods of control and
elimination of tuberculosis from herds having this disease. By carefully
conducted experiments and other forms of educational work the infectious
character of tuberculosis and the economic importance of preventative
measures have been demonstrated. The average stockman is well informed
regarding the character and economic importance of this disease, but there
is no general application of this knowledge, and tuberculosis is increasing
in dairy and breeding herds. The slow development of tuberculosis, and the
absence of visible symptoms during the early stage of the disease, are
responsible for this condition and the extensive infection of dairy and
breeding herds.

PREVALENCE OF THE DISEASE.--Tuberculosis is very prevalent among cattle and
swine in all countries where intensive agriculture is practised. It is a
rare disease among cattle of the steppes of eastern Europe and the cattle
ranges of the western portion of the United States. In countries where
dairying is an important industry, tuberculosis is a common disease of
cattle and hogs. The abattoir reports of Europe and the United States show
that tuberculosis is on the increase among domestic animals. The Bureau of
Animal Industry of the United States Department of Agriculture reports that
out of 400,008 cattle tested with tuberculin 9.25 per cent reacted. Melvin
states that the annual loss from tuberculosis in the United States is about
$23,000,000. In dairy herds in which the disease has existed for several
years, it is not uncommon to find from 25 to 75 per cent tubercular.

THE DIRECT CAUSE.--The direct cause of tuberculosis is Koch's _Bacillus
tuberculosis_. This is a slender, rod-shaped microorganisms (Fig. 88)
occurring in the diseased tissues, feces and milk of a tubercular animal.
It belongs to that small group known as acid-fast bacteria. The tubercle
bacillus is not really destroyed by external influences, and it may retain