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ACCOMPANYING PHENOJ^NA OF DENTAL DECAY. 161

real nature is an increased and lasting physiological activity,
which calls forth over-production of intercellular matter at the
expense of the cells and primarily of their oiFshoots."
Black "^ disputes the view that transparency is to be looked
upon as the expression of a vital process. He appears to regard
it as the earliest stage of disintegration. According to the ob-
servations which I have made in reference to transparency, I
am inclined to accept the vital theory. In my opinion we must
choose here between two possibilities : either the basis-substance
is decalcified and a form of transparency thus brought about, or
the tubules are partially or completely filled with a substance
which has a similar action upon light as the intertubular sub-
stance. A decalcification, however, has most certainly not taken place
in the transparency in question; this is sufficiently proved by
chemical analysis, while on the other hand many facts point to
a vital process.
1. We know that the diameter of dentinal tubules in normal
condition is much greater near the pulp than at the border of the
enamel, and that it is much smaller in senile than in young teeth.
These facts point to a gradual decrease of the diameter of the
tubules after the dentine has already been formed. We also
know that chronic excitations of any kind lead to " secondary"
dentine formation on the inner surface of the dentine. May
they not, then, also lead to an acceleration of the formation in the
domain of the fibrils ?
2. The microscopic examination of transparency shows as a
matter of fact a decrease in the diameter of the dentinal tubules
within the transparent zone. This at the same time signifies a
diminution in the size of the fibrils.
3. The transparency is characteristic of living dentine.
4. Chemical analysis gives results which agree with this
theory. According to my own determinations, dentine from the
transparent part of a number of teeth (about twenty-five) gave,
when dried at 102°-105° C, 71.9 per cent, ashes, while normal
dentine from the same teeth gave 72.1 per cent. A second calcu-
lation, made by a chemist, yielded for transparent dentine 69.5
per cent., and for the normal dentine from the same teeth 68.0.
We may conjecture from the rather small amount of ashes that
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