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ATROPHY OF THE TEETH. 37

apparently of usual firmness, but the enamel seemed to crumble
to pieces easilJ^ Not only the walls of the cavity crumbled, but
I could easily push a sharp explorer into the enamel of other
teeth anywhere. I took some of the cuttings from the enamel
walls of the cavity well beyond the decayed area and distributed
them in glycerin under a cover-glass, and with the microscope
found well-formed enamel rods that looked much like those that
had been separated by a very weak acid, or those taken from
the whitened enamel in backward decays.
This condition of the enamel had not rendered the teeth
more than ordinarily liable to caries, as was shown by the gen-
eral soundness of the teeth.
This condition reminded me strongly of the white spots
so often seen in the enamel of teeth that are in the main per-
fectly formed; and is undoubtedly of the same character. Fig-
ures 46, 47. The only difference seemed to be that the usual
white spots seen are covered with a very perfect glaze, or Nay-
smith's membrane, so that a sharp instrument will glide over
them. This man's teeth had no such glazed surface. A sharp
explorer would catch anywhere with very little pressure. In
fact, it would not glide over the surface at all. The teeth evi-
dently had not a normal Naysmith's membrane. The enamel in
the two cases seemed very similar to cutting instruments. Since
writing the above statement, another case has come under my
observation in which the incisal portion of the incisors and
cuspids and the occlusal portion of the bicuspids and molars
were covered with normal enamel, but a large part of the axial
surfaces were white enamel, much of which lacked the glazed
covering, or Naysmith's membrane. At all points this glazed
membrane was projected to some distance from the normal over
the abnormal enamel.
These cases, taken together with the frequent occurrence
of white spots, led me to the supposition that the failure of the
cementing substance between the enamel rods is a special form
of atrophy or abnoi'mality in formation to which the enamel is
liable. The occurrence of this in isolated spots, which are usually
of an ashy white color, is not very uncommon, but its occurrence
in the whole of the enamel in the teeth of a person is certainly
extremely rare. I have seen this in but the two cases mentioned,
in the one with abnormal form, in the other with normal form.
Nothing seems to be known of the pathology that brings
about this condition.
The study of such cases is of great importance, as it may