Pathogenic Bacteria

7Y WERCl 7. OS IS. 223

terested in tuberculosis, and, though exceedingly slow
and conservative in their movements, are disseminating
literature among doctors for distribution to their patients,
with the hope of achieving by volition that which they
would otherwise regard as cruel compulsion.

The channels by which the tubercle bacillus enters the
organism are varied. A few cases are on record where
the micro-organisms have passed through the placenta,
so that a tuberculous mother was able to infect her
unborn child. It is not impossible that the passage of
bacilli in this manner through the placenta causes the
development of tuberculosis in infants after birth, the
disease having remained latent during fetal life, for
Hireh-Hirsehfeld has shown that fragments of a fetus,
itself showing no tubercular lesions, but coming from a
tuberculous woman, were fatal to guinea-pigs into which
they were inoculated.

The most frequent channel of infection is the respira-
forv tract, into which the finely-pulverized dust of rooms
and streets enters. Probably all of us at some time in
our lives inhale living virulent tubercle bacilli, yet not
all of us suffer from tuberculosis. Personal predisposi-
tion seems of great importance, for it has been shown
that without the formation of tubercles virulent bacilli
may be present for considerable lengths of time in the
bronchial lymphatic glands—the dumping-ground of the
pulmonary phagocytes.

In order that infection shall occur it does not seem
necessary that the least abrasion or laceration shall exist
in the mucous lining of the respiratory tract. The
tubercle bacillus is a foreign body of irritating prop-
erties, and, lodging upon a cell, is soon engulfed in its
protoplasm, or, arrested by a leucocyte, is dragged off to
some other region in whose narrow passages a most hos-
tile strife doubtless takes place.

Infection also commonly takes place through the gas-
tro-intestinal tract b}' infected food. At present an over-
whelming weight of evidence points to the presence of