tated it must be evident that the bacterial origin
of disease depends upon the presence of a disease-producing fungus and
a diminution of the normal healthy tissue resistance to bacterial
invasion. If there is no fungus present, the disease caused by such
fungus cannot develop. If the fungus be present and the normal or
healthy tissue resistance be undiminished, it is probable that disease
will not occur. As soon, however, as overwork, injury of a mechanical
kind, or any other cause diminishes the local or general resistance of
the tissues and individual, the bacteria get the upper hand, and are
liable to produce their malign effect.

Many conditions favor the bacterial attack. The patient's tissues may
have an inherited peculiarity, which renders it easy for the bacteria
to find a good soil for development; an old injury or inflammation may
render the tissues less resistant than usual; the point, at which
inoculation has occurred may have certain anatomical peculiarities
which make it a good place in which bacteria may multiply; the blood
may have undergone certain chemical changes which render it better
soil than usual for the rapid growth of these parasitic plants.

The number of bacteria originally present makes a difference also. It
is readily understood that the tissues and white blood cells would
find it more difficult to repel the invasion of an army of a million
microbes than the attack of a squad of ten similar fungi. I have said
that the experimenter can weaken and augment the virulence of bacteria
by manipulating their surroundings in the laboratory. It is probable
that such a change occurs in nature. If so, some bacteria are more
virulent than others of the same species; some less virulent. A few of
the less virulent disposition would be more readily killed by the
white cells and tissues than would a larger number of the more
virulent ones. At other times the danger from microbic infection is
greater because there are two species introduced at the same time; and
these two multiply more vigorously when together than when separated.
There are, in fact, two allied hosts trying to destroy the blood cells
and tissues. This occurs when the bacteria of putrefaction and the
bacteria of suppuration are introduced into the tissues at the same
time. The former cause sapraemia and septicaemia, the latter cause
suppuration. The bacteria of tuberculosis are said to act more
viciously if accompanied by the bacteria of pu