uberculosis of the skin of the finger, known as _anatomical tubercle_.
Slight wounds of the feet in children who go about barefoot in towns
sometimes become infected with tubercle. Operation wounds made with
instruments contaminated with tuberculous material have also been known
to become infected. It is highly probable that the common form of
tuberculosis of the skin known as "lupus" arises by direct infection
from without.

[Illustration: FIG. 33.--Tubercle Bacilli in caseous material
x 1000 diam. Z. Neilsen stain.]

In the vast majority of cases the tubercle bacillus gains entrance to
the body by way of the mucous surfaces, the organisms being either
inhaled or swallowed; those inhaled are mostly derived from the human
subject, those swallowed, from cattle. Bacilli, whether inhaled or
swallowed, are especially apt to lodge about the pharynx and pass to the
pharyngeal lymphoid tissue and tonsils, and by way of the lymph vessels
to the glands. The glands most frequently infected in this way are the
cervical glands, and those within the cavity of the chest--particularly
the bronchial glands at the root of the lung. From these, infection
extends at any later period in life to the bones, joints, and internal
organs.

There is reason to believe that the organisms may lie in a dormant
condition for an indefinite period in these glands, and only become
active long afterwards, when some depression of the patient's health
produces conditions which favour their growth. When the organisms become
active in this way, the tuberculous tissue undergoes softening and
disintegration, and the infective material, by bursting into an adjacent
vein, may enter the blood-stream, in which it is carried to distant
parts of the body. In this way a _general tuberculosis_ may be set up,
or localised foci of tuberculosis may develop in the tissues in which
the organisms lodge. Many tuberculous patients are to be regarded as
possessing in their bronchial glands, or elsewhere, an internal store of
bacilli, to which the disease for which advice is sought owes its
origin, and from which similar outbreaks of tuberculosis may originate
in the future.

_The alimentary mucous membrane_, especially that of the lower ileum and
caecum, is exposed to infection by swallowed sputum and by food
materials, such as milk, containing tubercle bacilli. The organisms may
lodge in the mucous membrane and cause tuberculous ulceration, or they
may be carried through