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SPOXTAXEOUS HEALIXG OF DEXTAL DErAV. 203

whose teeth were in a very bad condition. All the front and
several, molar teeth were so much decayed that I entertained but
little hope of sa^^ng them.
I made temporary fillings in a number of the teeth, and
directed the little patients to be sent back again in two months.
At the end of this time they punctually returned, but as the
decay had apparently made no progress in the unfilled cavities,
nothing further was done. All of these unfilled cavities, eight
in the front teeth and three in the molars, healed completely,
the dentine became hard and smooth, and no further loss of
substance occurred.
The healed dentine retains the color of the carious dentine, is
almost as hard as the normal, and according to the determina-
tions of Dr. Cohn, of Berlin, contains a much greater percentage
of lime than decayed dentine. Microscopic examinations of
healed dentine have not, as far as I know, been made. In two
cases of healed decay I prepared some sections, but was not able
to note anything characteristic. The invasion of the bacteria in
the cases examined had been superficial, a fusion of the basis-
substance had not taken place, and the dilatation of the tubules
was confined to the external layer. Results obtained from the
examination of only two cases are, however, naturally not to be
relied upon too implicitly.
Opinions concerning the cause of this healing vary. Accord-
ing to some authors, it is to be explained by a renewed deposit
of lime-salts in the softened dentine. Such a deposit could of
course occur only in places not yet invaded by bacteria. Others
maintain that no vital process of any kind, as a redeposition
of lime-salts, can take place in the completely developed dentine.
They regard the healing as being due merely to the dehydration
(drying) of the dentine. As is well known, the decayed dentine
of extracted teeth becomes somewhat hard. Further experiments
are necessary to determine which of these views is correct.
K we accept the dehydration theory, we shall find it very difli-
cult, I am afraid, to explain how the dentine, continually bathed
with liquid as it is, can at all dry out in the human mouth, par-
ticularly how it can dry out in one tooth and not in others
which mav be decaved in the same mouth. We shall, further-