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HISTORY OF DENTAL SURGERY 193

in structure, etc. Also we read frequently of the selection and adaptation of
filling materials to teeth that are "frail in structure,' or to 'soft teeth,' and of
the adaptation of filling materials to hard, firm teeth, etc. In a search of the
literature for the basis upon which this idea of the differences in the con-
dition of the tissues of the tooth rests, it is found to be an interpretation
derived from certain clinical appearances. It often happens that the teeth of
certain persons have manifested little or no tendency to decay for years, and
then, almost without warning, rapidly progressing caries attacks a con-
siderable number at once, melting them down rapidly. The interpretation is,
that such teeth have become soft. This has been especially noted in pregnant
and nursing women. * * * Also the idea is prevalent that such teeth
have, in some way, lost lime salts; have, in a word, become less dense in
structure. As to the facts of the occurrence of this rapidly progressive caries,
where little or none existed before, there can be no question. * * * Also
many cases are observed in which caries has progressed rapidly for a time and
then practically ceased ; or has become easily controlled by the usual means.
The question at issue in this investigation is not as to the occurrence of the
conditions represented by rapidly destructive caries These cases occur as
represented. But the fuiestion presented here is the one relating tn the sup-
posed change in tooth structure. * * * Does this softening of the
structure of the tooth occur otherwise than by the direct action of the carious
process, and if so, in what degree!' Two well known facts have seemed to
argue against the interpretation that the clinical appearances mean soft or
softening teeth. First, the teeth are tlie hardest structures of the body, and
are of the lowest vital endowment as to self repair, and are therefore the
slowest in ^ital clumges. Second, caries, according to present accepted
theories, attacks the teeth from without, beginning upon the outside, and pre-
sumably the physical or vital condition of the teeth themselves has little to do
in the case. * * * The question as to the truth of these propositions will
be a principal subject for instrumental determination."
No account can be given here <>f the very elaborate series of tests and ex-
periments, nor any description of the instruments and apparatus used for the
purpose, and the conclusions to be derived from them can best be given in
Dr. Black's own words:
' CONCLUSIONS.
'
"From the facts developed in this investigation, it seems that the follow-
ing conclusions may be summarized.