Page 595 - My FlipBook

AMELIFICA TION. — GO 5
for I have found that the action of a 1-per-eent. solution of chromic
acid, even when not prolonged, results in complete decalcification and
removal of the entire enamel-covering of a tooth. Again, ]Mr. Tomes
says : '^ If dilute hydrochloric acid l)e applied to a section of enamel,
the axial parts of the fibres (prisms) are first attacked, and are dissolved
away ; so that if the section be transverse a fenestrated mass remains."
I think this phenomenon is capable of an opposite interpretation. If
we carefully study sections of enamel ground in the direction of the axis
of the prisms which have been exposed to the action of a very dilute
solution (of HCl), we find that the edge is dentated, and that the light
lines which mark the sides of the prisms end in the bottom of the inden-
tations, thus clearly demonstrating that the action of the acid is slightly
more rapid upon the peripheral than upon the axial portion of the
prism.
The next statement made by Mr. Tomes I can fully substantiate. It
is as follows : " During the formation of enamel the hardening salts are
deposited first in [aronnd) the periphery of the enamel-cells ; so that the
youngest layer of enamel is full of holes, each one of which corresponds
to the centre of a fibre (prism)." This I have observed as a constantly-
occurring phenomenon, and consider it as thoroughly substantiating my
position that the enamel-cell, or ameloblast, superintends the deposition
of the enamel-prism, and does not become directly calcified, as is held
by ]Mr. Tomes.
I look upon enamel as nothing more or less than a coat of mail sup-
plied by Nature to protect the dentine and subserve the processes of
mastication. The presence of any considerable organic material in the
enamel would be directly against the proper fulfilment of its office.
Nature, when left to herself, develops a beautiful and symmetrical
object perfectly capable of subserving its purpose, and any deviation
from this- standard is classed under the head of pathological conditions.
The fluids of the mouth are ?iorw«% alkaline or neutral, and against the
action of such conditions of the saliva the constituent parts of enamel
are proof. The enamel is not proof, however, against the action of
acids ; neither, indeed, was it intended to be.
The cross-striations found upon enamel-prisms as well as upon the
prisms of shells indicate the manner of their develojiment i. e. by
addition in length. This also accounts for the layers of pigment some-
times seen in these structures. They follow the course of the striated
lines, and are undoubtedly laid down at varying times in the course of
the formation of the prisms. The pigment seen in enamel is deposited by
the ameloblasts. Experiments have been made of feeding young guinea-
pigs upon madder, then allowing some time to elapse, after which the
madder diet is resumed. When killed and tlie tissues studied, the mad-
der dye was found to be deposited in bands or layers in the bone which
was developed while the experiment was being carried on. The bands
of unstained bone lying between the layers which had l:)een colored by
the dve represented the period whicli had elapsed between the different
experiments. It was found that the width of the bands was entirely
under the control of the experimenter, thus conclusively proving that
the pigmentation was from within, and that it was secreted by the bone-