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54 CARIES OF THE TEETH.

rapidly than a living one in similar circumstances
and hence the conclusion that vitality resists inju-
rious agents, and that the resistance will be in pro-

portion to the vitality.
All febrile conditions promote and facilitate decay,
and frequently in two ways : by diminishing the
general vitality, and by changing the secretions of
the mouth so that these act injuriously upon the
teeth. Accompanying such conditions, there is gene-
rally inflammation of the dentine ; and in such cases,
this always partakes of the general disorder so as to
become very susceptible to injury. All diseases,

indeed, that impair the vitality and change the secre-
tions, may be considered predisposing causes of decay,
and some even more ; dyspepsia, for instance, being
not only predisposing, but also exciting, since it pre-
pares in the stomach an acid that is almost continu-
ally thrown upon the teeth, and that acts upon them
with great energy. Residence in miasmatic regions,
is also a predisposing cause, inducing unfavorable
conditions.
Diminished vitality may result either from consti-
tutional or from local causes. These latter are such
as produce an irritable or diseased condition of the
contiguous parts, or an abnormal condition of the den-

tine, without the power to effect its decomposition.
Local causes of a diminution of vitality are not in