when planted along with other germs. It is very evident, therefore,
that bacteriology is a branch of botany, and that nature shows the
same tendencies in these minute plants as it does in the larger
vegetable world visible to our unaided eyes.

As the horticulturist is able to alter the character of his plants by
changing the circumstances under which they live, so can the
bacteriologist change the vital properties and activities of bacteria
by chemical and other manipulations of the culture substances in which
these organisms grow. The power of bacteria to cause pathological
changes may thus be weakened and attenuated; in other words, their
functional power for evil is taken from them by alterations in the
soil. The pathogenic, or disease producing, power may be increased by
similar, though not identical, alterations. The rapidity of their
multiplication may be accelerated, or they may be compelled to lie
dormant and inactive for a time; and, on the other hand, by exhausting
the constituents of the soil upon which they depend for life, they may
be killed.

It is a most curious fact, also, that it is possible by selecting and
cultivating only the lighter colored specimens of a certain purple
bacterium for the bacteriologist to obtain finally a plant which is
nearly white, but which has the essential characteristics of the
original purple fungus. In this we see the same power which the
florist has to alter the color of the petals of his flowers by various
methods of selective breeding.

The destruction of bacteria by means of heat and antiseptics is the
essence of modern surgery. It is, then, by preventing access of these
parasitic plants to the human organism (aseptic surgery), or the
destruction of them by chemical agents and heat (antiseptic surgery),
that we are enabled to invade by operative attack regions of the body
which a few years ago were sacred.

When the disease-producing bacteria gain access to the tissues and
blood of human and other animals by means of wounds, or through an
inflamed pulmonary or alimentary mucous membrane, they produce
pathological effects, provided there is not sufficient resistance and
health power in the animal's tissues to antagonize successfully the
deleterious influence of the invading parasitic fungus. It is the
rapid multiplication of the germs which furnishes a _continuous_
irritation that enables them to have such a disastrous effect upon the
tissues of the animal. If the t