flourish luxuriantly when planted together in the same fluid, somewhat
after the manner of pumpkins and Indian corn growing between the same
fence rails. Others seem unwilling to grow alone, and only flourish
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.