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42 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

of itself sufficient to prove the absolute incongruity of such an
idea. What would we think of a man who would put a piece
of meat in saliva, in the hope of keeping it from decay ? The
comparative rarity of diseases of the gums, in spite of the large
number of bacteria in the mouth, is due, not to the antiseptic
action of the saliva, but to the great power of resistance of the
gums, and to their comparative unsusceptibility to infectious
agents. It is well known that in removing tartar from badly kept
teeth we often wound the gums with impunity, in a manner
which on other parts of the body would be very likely to lead to
a serious infection.

2. The Buccal Mucus.
The secretion of the mucus-glands of the mouth is identical
with the mucus secreted by the submaxillary and sublingual
glands, which gives the saliva of these glands its viscous and
slippery character.
Hermann ^*^ calls the mucus "a clear, slimy, viscous alkaline
fluid" ; according to others, it has an acid reaction ; most proba-
bly the reaction of mucus, as well as of saliva, is subject to
variations dependent upon the general state of health. (See
also Chapter VIII.)
It is so difficult to obtain a pure secretion of the mucus-glands,
that the method proposed'by Kirk*^ seems to be the only means
of determining the reaction with any degree of certainty, for a
large number of cases. Mucus mixes with water without being
dissolved, is equally insoluble in alcohol, ether, chloroform, and
dilute mineral acids; soluble, on the other hand, in dilute alka-
lies and excess of mineral acids. It does not coagulate when
boiled, belongs to the albuminoids, and serves as a nutrient for
bacteria.
3. Dead Epithelial Cells.

These cells, for the most part from the surface of the mucous
mernbrane, form a flaky precipitate in saliva left standing, or are
deposited, mixed with mucus and particles of food, upon the teeth,
particularly in places which are not exposed to the friction of
mastication. Under the microscope they appear as flat, irreg-