Page 133 - My FlipBook

TWELFTH LECTURE.

In my last lecture I spoke to you of the material con-
ditions which bring about immunity or susceptibility to dis-
ease. I want to hold your attention to this for a time yet,
that you may become as familiar with it as it is possibje in this
way. Not, perhaps, because you will have use for it in gen-
eral medicine—for I do not suppose that many of you will
treat typhoid fever, yellow fever, small-pox, measles, whoop-
ing-cough or this class of diseases of which I spoke in my
—
last lecture ^but to illustrate the principles of pathology
which you must follow more or less in the future. The time
is coming when the dentist will have to know more about
these subjects if he is to be a successful practitioner of den-
tistry, because their connection with caries of the teeth and
the diseases of the mouth with which we deal is becoming
more clearly established.
I spoke particularly of the defensive proteids, of the
alexins and the antitoxins, and their influence in promoting
immunity from disease. \\'e may now divide im-

munity into four classes : Xatural ijiuniuiity, naturally acquired
immunity, accidoitally acquired iiinuuiiity and artifici-
ally acquired iuiniuuity. You will remember that the alexins
are bodies that act as antiseptics, that prevent the growth of
micro-organisms in the body, and the principles of this con-
stitute what is known as natural imnuinity. Certain species
of animals are naturally immune to certain diseases or
are generally immune to bacterial diseases. Take the
carnivra, for instance ; they are what bacteriologists de-
note as refractory animals is difficult to get bacteria to
; it
grow in their tissues, and they are found to have large quan-
tities of this material in their blood. So certain animals are
naturally immune to certain diseases. This is known as natu-
ral immunity.
Naturally acquired immunity has its strongest illustration,
perhaps, in the diseases of infancy, that group of diseases that
affect children particularly, as measles, whooping-cough,
scarlet fever, diphtheria, etc. Now, persons, as they progress
from childhood to adult age. acquire immunity from these
diseases. This is from the development of certain princi-

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