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ATROPHY OF THE TEETH. 23

been unusually warm, the interglobular spaces were again filled
with balsam. The shadow, however, remained, and is presented
in Figure 28. It has since been found that the condition pre-
sented is common to a considerable number of the slighter
atrophic injuries.
Figure 29 is a photomicrograph of a labio-lingual section cut
from near the mesial side of an atrophied tooth so that the line
of interglobular spaces is cut through diagonally. This gives
an exaggerated view of the zone of injury to the dentin, but will
serve to impress the fact that these injuries are very severe.
This presents this subject from its gravest to its slightest
degree, in sufficient variety of cases to render the conditions
intelligible.
Atrophy of the FmsT Permanent Molars.
Atrophy of the first permanent molars should receive some
special consideration because of its greater frequence and
because it so generally leads to early and rapid caries beginning
in the atrophied portion. The plan of injury does not differ
from that in atrophy of the anterior teeth, but the details of the
injury are different because of the wide difference in the form
of the tooth. The greater frequence of the occurrence of atrophy
of these teeth is due to the earlier beginning of calcification. In
dissections of the jaws of the fetus at term, I have usually found
the calcification of this tooth just begun on the points of the
cusps. Sometimes there are only small spiculae, in other cases
a more considerable part of the cusps is calcified, but I have
never seen the calcification so advanced at birth that the cusps
were united by calcified tissue, and evidently they are not so
united rmtil much later. On the other hand, it was only occa-
sionally that the least bit of calcification had occurred on the
central incisors. More often calcification does not begin on these
until about the end of the first year. Therefore, an illness that
brings about serious malnutrition during the first year of the
child's life is liable to wreck the occlusal surfaces of the first
molars, while all of the other teeth escape injury.
Atrophy of these teeth occurring so early is very charac-
teristic if seen soon after the eruption of the teeth and before
further injury has occurred by breaking away the sharp spiculae
representing the malformed cusps or by caries. But it is exceed-
ingly difficult to obtain specimens from which to make illustra-
tions. If the atrophy has occurred very early, or before the
enamel plates forming the lobes of the teeth have joined together,