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166 HUNTEK ON THE TEETH.
The fore Teeth in the lower Jaw appear to be less subject
to this disease than any of the others ; the fore Teeth in the
upper Jaw, and the grinders in both, are of course more
frequently affected.
This disease and its consequences seem to be peculiar to
youth and middle age ; the shedding Teeth are as subject to
it, if not more
so, than those intended to last through life
;
and we seldom or ever see any person, whose Teeth begin to
rot after the age of fifty years.
This might be supposed to arise from the disproportion that
the number of Teeth, after fifty, bear to them before it ; but
the number of diseased teeth after fifty do not bear the same
proportion, (e)
(e) [Numerous theories and hypotheses have from time to time been put
forth as to the cause of dental caries. These causes may be arranged under
the two heads of predisposing causes and of exciting or proximate
causes. Among the predisposing causes may be enumerated original
imperfections in the tissues of the teeth, such as cracks or imperfections
in the enamel, and white opaque imperfectly-formed spots. The honey-
coombed depressions which are so often seen in the enamel, and also
the transverse depressions which surround the crown of the tooth like
so many rings, are sure indications of an imperfectly formed dentine.
Microscopic sections of such teeth show the existence of open spaces in
the dentine, where calcification has not taken place. These spaces are
black and opaque when filled with air, or clear and apparently void,
when the tooth is saturated with a transparent fluid, such as oil, water,
or canada balsam. Crowding irregularity, and want of care in cleaning
the teeth, must also be classed amongst the predisposing causes.
Another and important predisposing cause is the occurrence of certain
constitutional disorders which exhaust the powers of the body, leaving
the patient in a state of extreme debility, and with a long period of
convalescence before he is restored to health. It is well known that
the eruptive fevers of childhood are often followed by the loss of a por-
tion of the jaw bones, together with the included germs of the perma-
nent teeth. (1) In a similar manner the more severe fevers of adult life

(1) See Mr. Salter's cases and remarks. Guy's Hospital Reports, Vol. VI.
Third Series.