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190 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

by the pressure of the fungal masses in the tubules, by which a
compression of the walls is caused. This supposition receives
support from the fact that a thickening of the dentine may also
be observed around the larger masses of bacteria in decayed
dentine, ^""hen examined under the microscope, the dentine
bordering such masses may often be seen to ditfer from the sur-
rounding tissue by its higher refractive power.
By the action of acids upon carious dentine I have succeeded
in producing appearances greatly similar to, if not identical with,
the thickening described above. The resisting dentinal sheaths
(tubules), especially such as are filled with bacteria, are loosened
from the basis-substance and then more or less bent at the

Fig. 90. Fig. 91.

\ < 0.

Appearance of Dentinal Sheaths - [ - i" " ' r-
produced by the action of strong : ^ { '^ [
acid on decayed dentine.
Rod-shaped, Non-Vegeta-
I](i0 : 1.
ble Elements in de-
cayed dentine.
loosened extremities (Fig. 90, «, 6), or flattened out (Fig. 90, c),
or, lastly, torn from their beds altogether (Fig. 90, d). On the
whole, however, it will be seen that I am not able to throw nmch
light upon this question, and must leave it for further investiga-
tion to settle.

The appearance of rod-shaped elements or fragments in the tubuli
of decayed dentine was first noticed by J. Tomes, and is no
rare phenomenon either in natural or artificial decay. Fig. 91,
taken from a specimen of artificial caries, gives a fair idea of
it. J. Tomes ^'® endeavored to explain this phenomenon by the
consolidation of the dentinal fibrils, while AVedl ^^ regards this
view as not proved. Later Tomes "^ writes, "These rods may
be portions of consolidated fibrils, or they may be bits of the