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162 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

the dentine was not thoroughly dried before combustion ; this
hitter determination is therefore not quite reliable, but at any
rate shows that there is an increase rather than a decrease of
lime-salts. The general conception, however, that this theory is
compatible only with a high percentage of lime-salts is not quite
correct. A formation of new dentine, whether it be at the per-
iphery of the pulp or in the domain of the fibrils, does not occur
without a preceding solidification of the outer layer of the odon-
toblasts or fibrils. If, therefore, a new formation of dentine
takes place in the tubules at the expense of the dentinal fibrils^
this occasions not only an increase of lime-salts, but also simul-
taneously an increase of the glue-giving basis-substance. We
may therefore have a consolidation of the dentine, although
analysis may not detect any marked increase in the percentage
of lime-salts. In conclusion, this theory must not be confounded
with the old calcification theory. The latter demands an im-
pregnation of the fibrils with lime-salts only, the former a partial
or total conversion of the fibrils into normal dentine.
2. Pigmentation of the Tissue in Dental Decay.
The pigmentation or discoloration usually attending decay of
enamel or dentine is another secondary process which has erro-
neously been viewed as a stage of decay. Every degree of dis-
coloration may be observed, from the normal color of the tissue
to a yellowish, yellow, yellowish-brown, dark-brown, black. In
the very first appearance of decay no discoloration is visible.
This absence of discoloration is especially remarkable in second-
ary caries of enamel, the tissue being converted into a perfectly
white powder.
ISoY does rapid caries show any or but very little discoloration
in the deeper parts, while chronic caries always exhibits a dark
€olor, dark brown to black; in other words, the intensity of the
discoloration is in inverse jirojportion to the rapidity of the progress of
the disease. Besides, the discoloration ot dentine does by no means
occur in decay only. Wherever the dentine is laid bare, it may
be more or less discolored in time. The black discoloration is
especially common in worn-otF teeth, and, indeed, not only in the
case of smokers, but also of non-smokers, nor is it rare for the