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774 DENTAL CARIES.

special disease has as its basis a change in the physiological qualities or
activities of the cellular elements, as in the cancers, there is something in
the physiological constitution of the individual rendering the cellular
elements peculiarly liable to this form of excitement. If the particular
disease has a fermentation as its basis, the fluids of the individual must
furnish a favorable soil for the growth of the fungus of that fermenta-
tion. Again, persons acquire a temporary susceptibility to certain dis-
eases, not from a condition of ill-health that is in any way manifest,
but apparently through some minor changes, as yet impossible of anal-
ysis, in the action of the vital forces of the organism or constitution of
the fluids. If we can trust the combined observations of the profession,
changes that are of the same order certainly occur in the predisposition
to caries. Why is it that pregnant women become temporarily more
susceptible to caries? Certainly not from any change in the structure
of the teeth themselves, rendering their lime salts more easy of solution
by an acid. Of all the tissues of the body, the teeth are least prone to
structural changes consequent upon variations in nutrition, and there-
fore are least liable to temporary susceptibility to disease on that
account.
The saliva is certainly in a large degree antiseptic in its qualities, and
opposes the process of fermentation, notwithstanding the fact that fer-
mentation, in some of its forms, is continually in progress in the mouth.
It is practically impossible to protect wounds of the mouth from micro-
organisms, yet these wounds are less liable to sepsis than any others in
the organism that are exposed to external influences.
It is possible that what have been noted as the antiseptic qualities of
the saliva as seen in its relation to wounds in the mouth may be due
to the continued irrigation of the surfaces by the flow of fresh saliva,
Mdiich washes away septic organisms or their products. This in a large
degree explains the occurrence of decay in protected points only, and fur-
nishes a reason for the rare occurrence of caries in the lower incisors.
When all of the facts known to us are considered, the most plausible
supposition is that there are diflerences in the saliva that in some cases
render it an unfavorable soil for the propagation of the peculiar fermen-
tation found to be the cause of caries. In other cases it becomes a very
fav^orable soil for the growth of this peculiar fungus, and caries is cor-
res])ondingly active. When we look around us and gather together the
facts at our command in regard to the susceptil)ilities of those forms of
life which we know, and see how they affect each other in ways that seem
inscrutable, these suppositions, while losing none of their mystery, are
seen to be in harmony with those forced upon us in other fields of
observation.

Morbid Conditions of the Fluids of the Mouth.
By most authors who in tlie ]iast have examined the "subject morbid
conditions of the saliva and of the mucus of the mouth have been con-
sidered as among the active causes of caries. In view of the expla-
nation given in the previous ]>ages, this becomes impossible. If the
causes of caries have been correctly detailed, the influences favorable to