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192 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

(Fig. 94). This would seem to justify the hypothesis that after the
formation of these lime-casts an invasion of the micro-organisms
and an enlargement of the tubules takes place, loosening the easts
from the walls of the tubules. At any rate, we have here not a
vital but a chemical process, since the fragments in question are
very common in artificial decay. The fact that I have never
noticed the characteristic crystals of sulphate of lime, after treat-
ing the separate rods with sulphuric acid, appears at first to tell

Fig. 95.

Rows OP Shining Granules in the Tubules, in decay of a tooth worn on a plate.
against the hypothesis that these elements consist of lime-salts;
the quantity of lime in one fragment may, however, be too small
to give the crystal test.
The rods do not dissolve in organic acids ; they even become
more distinct after treatment with lactic and acetic acids. Three
tests with alcohol and chloroform had no effect.
The occarrmce of rows of shmiiig, irregular grains in the tubules
(Fig. 95) is frequently observed in the beginning of caries.
Sometimes this deposit is made in a zone just in front of the
advancing caries, so that many have regarded it as an attempt