y be due to the toxins or poisonous matters that are
given off by the parasite while it is living in the host's body. Thus it
is believed that the malarial patients usually suffer less from the
actual loss of red blood-corpuscles that are destroyed by the parasite
than they do from the effects of the poisonous excretions that are
poured into the circulation when the thousands of corpuscles break to
release the parasites.

One other point in regard to the relation of the parasite to its host
and this part of the subject may be dismissed. From our standpoint we
look upon the presence of parasites in the body as an abnormal
condition. From a biological standpoint their presence there is
perfectly normal; it is a necessary part of their life. We think that
they have no business there, but from the viewpoint of the parasites
their whole business is to be just there. If they are not, they perish.
And when we take a dose of quinine or other drug we are killing or
driving from their homes millions of these little creatures who have
taken up their abode with us for the time being. But they interfere with
our health and comfort, so they must go.

CHAPTER II

BACTERIA AND PROTOZOA

BACTERIA

On the border line between the plant and the animal worlds are many
forms which possess some of the characteristics of both. Indeed when an
attempt is made to separate all known organisms into two groups one is
immediately confronted with difficulties. In looking over the text-books
of Botany we will find that certain low forms are discussed there as
belonging with the plants, and on turning to the manuals of Zooelogy we
will find that the same organisms are placed among the lowest forms of
animals. The question is of course of little actual importance from
certain points of view. It serves, however, to show the close relation
of all forms of life, and from a medical standpoint it may be of very
great importance owing to the difference in the life-habits, methods of
reproduction and methods of transmission of many of the forms that cause
disease. We have already seen that none of the diseases that are caused
by animal parasites is contagious, while many of those caused by
bacteria are both contagious and infectious.

Just over on the plant side of this indefinite border line are the
minute organisms known as bacteria. Their numbers are infinite and they
are found everywhere. The majority of them are beneficial to mankind in
one