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196 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

periment they obtained softening, bntno discoloration. A micro-
scopical examination does not appear to have been made.
They came finally to the conclusion that artificial decay is an
impossibility, because the bacteria of decay lose their specific
power when cultivated out of the mouth.
Nevertheless, I afiSrm that a destruction of the tooth-substance
may be brought about artificiall}^ which the most practiced
microscopist will not be able to distinguish from real decay as
it occurs in the human mouth. In fact, not one of the many
microscopists who have made the attempt has been able to
determine which of a given numljcr of preparations were arti-
ficial and which natural.
The chief object of ray experiments was to produce the micro-
scopic appearances of decay of the teeth, since it had already
been proved by Magitot beyond doubt that by various means
?/iacroscopical appearances may be produced which are identical
with those found in decay.
I cut up a number of teeth which were perfectly sound, but
of different density, into pieces of different size, and placed them
in a mixture of saliva and bread. This mixture was kept for
three months at a temperature of 37° C, and during the course
of the experiment repeatedly renewed. At the end of this time
I showed a number of these pieces to a w^ell-known dentist of
thirty-three years' standing, and asked him if these were not
peculiar cases of decay. He replied by saying that he saw such
cases every day in his practice. In many pieces the dentine was
softened through and through, in all to a considerable depth.
When the softening had penetrated through the dentine to the
inner surface of the enamel, the latter was found covered with a
layer of white powder exactly as it is found in natural decay.
Cracks and fissures in the enamel had an opaque, whitish appear-
ance, and in many cases could be easily penetrated by a sharp
instrument. At the neck of the tooth the dentine was likewise
much softened, though not to so great a degree as on the
crown. The border of the enamel was rough, and so brittle that
in many places an instrument could be inserted betw^een the
enamel and the dentine. On the grinding-surface, in such cases
where the structure of the tooth was imperfect and full of fissures