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ATROPHY OF THE TEETH. 31

pit to the outer surface of the enamel, leaving an opening the
full depth. Or this may be filled in part by a dark material
not resembling enamel. Or, again, the surrounding enamel rods
may close over it, partially or completely obscuring the pit, so
as to form a smooth enamel surface over it. In Dr. Callow's
case, described later, the deformity consists mostly in numerous
examples of these whorls, many of them extending deeply into
the dentin. In Figure .'>4 the enamel rods close over the whorl
of rods imperfectly, but leave a ragged pit in the surface of the
enamel. That these whorls are sometimes closed over so as to
give a perfect enamel surface, is shown in Figure 42, from the
occlusal surface of a bicuspid from Dr. Callow's case. These
definite whorls are at the dento-enamel junction, or actually
partly within the dentin. But many pits are formed within the
usual thickness of the enamel without disturbance of the line
of the dento-enamel junction, as shown in Figure 35. In most
of these cases there is much disturbance of the direction of the
enamel rods in the immediate neighborhood as the rule. In some
there seems to be a failure of the enamel organ to perform its
function of rod formation at the particular spot. In and about
many of these pits there is deep discoloration. Many times the
dark color is confined to the pit itself, which is partially filled
with a substance strongly resembling the chittinous covering of
insects in appearance and in which no enamel rods can be made
out. In other cases the dark color extends broadly in, or among,
the enamel rods about the pit.
In these pits the disturbance follows the general direction
of the enamel rods in the locality. This is as true of the pits
that accompany atrophy as those that occur without atrophy.
In this the pit is distinctly different from the other injuries to
the enamel in atrophy, for these as uniformly follow the lines of
Ritzeus, i. e., the lines of accretion.
I have been unable to form any idea of the pathology con-
cerned in the formation of these pits. Their special prevalence
in atrophy cases indicates that they are due to disturbances of
nutrition. They consist essentially in a failure in the formation
of enamel rods. But such remarkable disturbances as those
shown in Dr. Callow's case, described next, indicate that there
may be some other pathological element not yet understood.
Histologically, they seem to be a very distinct form of atrophy.
The rule is that these pits need no treatment. They rarely decay,
but as there is a slight opening and the tissue is often black
or dark colored for a little bit around it, dentists frequently