Page 616 - My FlipBook

626 DENTAL EMBRYOLOGY AND HISTOLOGY.
to differentiate the ameloblastic layer. Although these cells occupy the
position where the first formation of enamel will make its appearance,
the older layer {of), in the central part of the figure, remains unchanged,
the process of infiltration having not as yet begun. But on either side
of these unaltered cells, at .sv, sr, the stellate cells are very plainly
shown. Between the stellate cells larger and smaller spaces occur.
This stellate appearance is largely due to post-mortem changes. The
actual spaces which occur between the stellate cells are chiefly the result
of shrinkage. If an osmic-acid solution (1 per cent.) and alcohol, equal
parts, be injected underneath the mucous membrane covering the jaws
of an 8 or 10 cm. pig while the embryo is yet warm, and then immersed
in a similar solution to harden, the post-mortem changes in the cells
will be to a greater or less extent arrested. If we lift the mucous
membrane from its bed after the tissue is sufliciently hardened, the
enamel organs will adhere and bring up with them their papillae. The

Inner Tunic Enamel Organ Porcine Embryo (6 cm. X 250) : i/, inner tunic; o/, older layer; sr,sr,
stellate reticulum.
enamel organ is thus isolated from all surrounding calcified tissue, and
we are able, after embedding, to make sections without waiting for the
bone of the jaw to be decalcified, decalcification necessitating the use of
acids which will cause more or less change in the soft cells in the interior
of the enamel organ. Tlie fibrillated condition of the stellate cells seen
in specimens hardened in JMiiller's fluid, chromic acid, etc. is demon-
strated, by the osmic-acid method, to be in reality a broad mesh. The
reticular appearance seen in the chromic-acid preparations results from
post-m()rt(!m shrinkage in the older cells which fill the interior of the
enamel organ. I fully believe that if we could examine these cells at
once, before any shrinkage occurs, we should be able to prove the fact
that in life they are not stellate, but large polygonal cells. I am led to
this inference by the above-noted experiments^ the better methods of
technique showing a less fibrillated appearance than do other methods
Avhich allow more shrinkage.
Sections of isolated enamel organs might be obtained by the freezing
method were it not for their minute size ; if this could be done without
the use of any hardening fluids, better studies could be made. It is to