rcentage of fat generally diminishes.
Whenever the udder shows physical manifestation of this disease, the
milk almost invariably is rich in tubercle bacilli.

Tubercle organisms may also appear in milk of animals in which no
physical symptoms of the disease are to be found. This fact has been
demonstrated by microscopic and animal experiments, but it is also
abundantly confirmed by the frequent contraction of the disease by
calves and hogs when fed on factory by-products. This latter class
of animals is particularly dangerous, because there is no way in
which the danger can be recognized.

[Illustration: Fig. 17.--a Tuberculous Animal.

The animal appears perfectly healthy although she has had the
disease for five years.]

It has also been proven that milk may become infected through the
feces. In coughing up material from the lungs and associated glands,
the matter is swallowed, instead of expectorated, as in man. The
organisms retain their vitality in the intestine, and are voided in
the feces. Under ordinary conditions, the flanks and udder become
more or less polluted with such filth, and the evidence is
conclusive that infection of milk is not infrequently occasioned in
this way. The fact that hogs following tuberculous steers in the
feeding lots are very likely to acquire the disease is explained by
the presence of tubercle organisms in the manure of such animals.

[Illustration: Fig. 18.--a Tuberculous Animal.

The last stages of generalized tuberculosis. Note the emaciated
condition.]

It must be kept in mind that many animals may be infected with
tubercle bacilli and therefore have tuberculosis in the incipient
stages, without their being able to disseminate the disease to
others. In the early stages, they are bacillus-carriers without
being necessarily dangerous at that particular time, but the
possibility always exists, as the disease develops in the system,
that the trouble may assume a more formidable character, and that
slowly developing chronic lesions may become acute, and "open," in
which case, the affected animal becomes a positive menace to the
herd. As the time when the lesions change from the "closed" to the
"open" type and the animal becomes a source of danger cannot be
determined, the only safe way to do is to exclude the milk of all
tuberculous animals from the general supply, whether for direct
consumption, or for manufacture into dairy products and to look upon
every diseased animal