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OF THE BONY PART OF A TOOTH. 49
we might suppose to be organized and vascular. The earth is
in very considerable quantity ; it remains of the same shape

of the constituent bodies being ultimately lost in the uniform fusion of
the whole into one compact mass." " In the discovery of the substitution
of the globular for the crystalline form of these two salts of lime, Mr
Rainie considers he has found an explanation of the process of calcifica-
tion, not only of bone and teeth, but also of the formation of shells." (1)
In many teeth, the original dentine globules are indicated by faintly-
traced arched lines ; but the more perfectly calcified the tooth, the more
completely will fusion have taken place.
The dentinal canals are generally held to be permeated during life by
a nutrient fluid. Mr Tomes, however, has announced the. discovery that
each dentinal tube is permanently tenanted by a soft fibril, which passes
from the pulp into the tube, and follows its ramifications. The dentinal
fibril he describes as consisting of an almost structureless tissue, trans-
parent, and of a comparatively low refractive power. He has not
hitherto been able to determine whether it is tubular or solid. " In
some cases," he writes, "there is an appearance of tubularity ; but, being
cylindrical, this may be a mere optical effect. When accidentally
stretched between two fragments of dentine, the diameter of the fibril
becomes much diminished; and when broken across, a minute globule of
transparent but dense fluid may sometimes be seen at the broken end,
gathered into a more or less spherical form." These appearances may
lead to the surmise that the fibril, like the white fibrillte of nerves,
consists of a sheath containing a semi-fluid matter ; but such a conclusion
is not to be accepted without farther evidence. Mr Tomes is unable to
state the manner in which the fibrils he describes are connected with
the pulp. He has traced them for a short distance into its substance,
but at present cannot decide whether they terminate in cells, or are in
any way connected with the nerves of the pulp. Although he does
not take upon himself to affirm that these fibrils are of the nature of
nerves, he yet regards them as the means by which sensibility is com-
municated to the dentine. (2) These observations are highly interesting
and important, but at present they require confirmation.
Nasmyth took a different view of the structure of dentine. From
his observations, he was led to deny the existence of the dentinal tubuli.
He believed that " the so-called tube was in reality a solid fibre, com-
posed of a series of little masses succeeding each other in a linear direc-
tion, like so many beads collected on a string." The matrix—or, as he
terms it, inter-fibrous substance—he describes as being originally cellular
in composition ; and he maintains that the baccated fibres are, in fact,
rows of persistent nuclei belonging to the cells of which the inter-fibrous
(1) Tomes' s System of Dental Surgery, pp. 298, 299.
(2) Tomes, op. cit, pp. 282-288.