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22 PATHOLOGY OF THE HARD TISSUES OF THE TEETH.

line of interglobular spaces is almost obscured by being tilled
with balsam in mounting the section.
Figure 25 represents a case that was apparently of the
mildest description. The only outward appearance was a band
of slightly dark color across the labial surface of the tooth. One
not searching for cases of this character might have passed the
tooth as normal. The tissue reveals a pronounced disturbance
in the same particulars as in the more severe cases, only not so
grave. The enamel rods pass through all of the darkened lines
without a break, and there are almost no interglobular spaces in
the dentin. A sharp curve and recurve in the dentinal tubules
give the appearance of a very distinct line of injury, however.
The line of the labial dento-enamel junction is also considerably
disturbed.
The next case is very curious in several respects. It is a
bicuspid tooth that showed a very slight groove in the enamel
not far from the gingival line. It was covered by the overlap-
ping gum margin, except on the buccal surface. The whole tooth
was, perhaps, as white as any normal tooth and was without any
discoloration along the line of the groove, except that caused
by a deposit of dark, closely adherent serumal calculus at several
points. A photograph of this groove was but a partial success,
as is shown in Figure 26. The tooth was then divided mesio-
distally, preparatory to grinding sections. In examining the
halves with a pocket lens, a curious zone of injury in the dentin
was discovered, which was photographed at once as an opaque
object, which is represented in Figure 27. Two sections, two
thousandths of an inch thick, were prepared and mounted with-
out removing them from the cover glass on which they were
ground. The sections were beautiful. No one would suspect
that there was any zone of injury in either dentin or enamel.
The disturbance of the line of the dento-enamel junction and in
the one section a clinging bit of serumal calculus were the only
abnormalities discoverable by microscopic examination. The
only way I could explain this was that the something that had
been seen and photographed had become obscured by the balsam.
The balsam was dissolved out and the section dried. A zone of
fine interglobular spaces was then found with another singular
appearance in the form of a broad line of demarkation, that could
not be explained. The section was remounted in a very stiff
balsam without using anything to clear the dentin, with the
expectation of making a photomicrograph the same evening.
Something prevented, and by the next evening, the day having