Page 57 - My FlipBook

bi)
The enamel is situated upon all that part of a tooth which
in the healthy state of the gums is not covered by them. This
portion of a tooth is called the body or crown. It is formed
by the membrane which invests the pulp. When a shell of
bone has been formed upon the pulp, this membrane secretes
a fluid, from which a very white soft substance is deposited
upon the bone ; this is at first of a consistence not harder
than chalk, for it may be scratched or scraped off by the
nail ; it however soon grows hard, and seems to undergo a
process similar to that of crystalization, for it takes a regu-
lar and peculiar form.
The deposition of the enamel continues nearly as long as
a tooth is contained within the membrane. It is always
most in quantity upon those parts where its formation first
it is thicker upon the edges and grinding surfaces of
began ;
the teeth, than upon the sides, and it gradually becomes thin-
ner as it approaches the necks of the teeth. A tooth, when
sawn through, shows the arrangement of the enamel ; and
as it requires more heat to blacken and burn this hardest
part of the animal frame than the bony part of the tooth,
we can, by exposing it to the effects of fire, obtain a still
more distinct exhibition of it. By the time the enamel is
completely formed, the tooth has risen so much in the sock-
et, that by its pressure it occasions an absorption of the
membrane, which completely prevents any further addition
of enamel.
When perfect the enamel of the teeth is so hard, that a
file, in cutting it, is soon worn smooth, and when struck with
it, sparks of fire will be elicited ; an effect I have several
times produced with human teeth, and which will be very
readily seen, by striking the teeth of large animals with steel,
particularly those of the Hippopotamus.