Page 155 - My FlipBook

OF THE FORMATION OF THE ENAMEL. 139
ossify, a thin covcriug of enamel is spread over them, which
increases in thickness till some time before the Tooth begins to
cut the Gum.
The Enamel appears to be secreted from the Pulp above
described, and perhaps from the Capsula which incloses the
body of the Tooth. That it is from the Pulp and Capsula
seems evident in the horse, ass, ox, sheep, &c. therefore we
have little reason to doubt of it in the human species. It is a
calcareous earth, probably dissolved in the juices of our body,
and thrown out from these parts which act here as a gland.
After it is secreted, the earth is attracted by the bony part of
the Tooth, which is already formed ; and upon that surface it
crystallizes.
The operation is similar to the formation of the shell of the
egg, the stone in the kidneys and bladder, and the gall stone.
This accounts for the striated crystallized appearance which
the Enamel has when broken, and also for the direction of these
Stride. *
The Enamel is thicker at the points and basis than at the
neck of the Teeth, which may be easily accounted for from its
manner of formation ; for if we suppose it to be always secreting,
and laid equally over the whole surface, as the Tooth grows,
the first formed will be the thickest ; and the neck of the Tooth,
which is the last formed part inclosed in this Capsula, must
have the thinnest coat ; and the fang, where the Periosteum
adheres, and leaves no vacant space, will have none of the
Enamel.
At its first formation it is not very hard ; for by exposing a
very young Tooth to the air, the Enamel cracks, and looks
rough : but by the time that the Teeth cut the Gum, the
Enamel seems to be as hard as ever it is afterward ; so that the
air seems to have no effect in hardening it.
* The Author has made many experiments on the formation of
different Calculi, and finds they are formed by crystallization, which
were communicated to his brother, and taught by him to his pupils in
1761, and which he proposes to give to the Public as soon as his time
will permit.