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92 PATHOLOGY OF THE HARD TISSUES OF THE TEETH.
beginnings of this, which constitutes the initial lesion, without
which caries of dentin never occurs, was left untouched. These
constitute the principal clinical features of the disease we are
treating. Our knowledge of them is, as yet, but partially devel-
oped, particularly in that the systemic conditions of suscepti-
bility and immunity are but indefinitely known; and observers
do not yet agree as to the especial relations of acid saliva and of
microorganisms to the particular processes in the earlier parts
of the beginning of caries of enamel.

Occlusal, Surface Decays in Molars.
ILLUSTRATIONS: FIGURES 68-71, 104-106.
Principal clinical features: (1.) Beginning in pits,
absence of superficial spreading. (2.) Rapid burrowing along
the dento-enamel junction. (3.) Spreading in the dentin in true
conical form. (4.) Great softening of dentin in advance of the
decomposition of the organic matrix. (5.) Very large decays
often occurring while the opening to the surface remains small.
These characters are common to decays beginning in pits and
fissures wherever found.
The conical form of decays of dentin beginning in pits, in
the occlusal surface or elsewhere, the spreading along the dento-
enamel junction, and the absence of spreading superficially on
the surface of the enamel, have been considered in previous
articles and some principal illustrations, Figures 68-71, given.
For the further illustration of the clinical features, the Figures
104-106, inclusive, are here provided. It will be seen that Figure
104 and other figures of this group show the same form of
decayed area more or less perfectly, the detail being different
in some degree on account of size of the decayed area or the
particular form of the surface of the tooth about it. In each
case illustrated, the direction of force in the use of the chisel
in opening the cavity so as to fully uncover the area of decay,
may be studied. The case illustrated in Figure 104, considering
the tooth as a whole, is complicated by two other decays, both
of them in the distal surface ; one a very shallow decay, begin-
ning in the enamel at the usual point of beginning decays, and
the other a decay beginning in the cementum and penetrating
into the dentin at the gingival line. This latter is a serious
complication in the clinical sense, which has arisen from neglect
of the leakage of food into the interproximal space. In Figures
105, 106, the openings through the pits, in which the decay has