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sensitiveness in the hyaline zone of Tomes—the most sen-
sitive area except that close against the dento-enamel junc-
tion—and we conclude from that that the acids which dis-
solved out the lime salts from the dentin do not destroy
the fibrils. The fibrils seem to be destroyed by the inva-
sion of the micro-organisms, for that zone between the in-
vasion of the micro-organisms and the line of perfect den-
tin is the zone of greatest sensitiveness in decayed areas.
This is true of all cases of decay that is going on rapidly,
or making fairly rapid progress, and particularly of young
persons ; it is greater usually in young persons than in older
persons ; children suffer more from sensitiveness than adults,
as the rule. In these cases in which decay is very slow it
often happens that the fibrils have died in the otherwise
unaffected dentin. At least the evidence seems to be that
the fibrils are often destroyed for a considerable distance
beyond the portion of dentin that has been affected by the
decay, or that has lost Hme salts. Often in the preparation
of specimens of old decays we will find a dark streak run-
ning down to, or nearly to, the pulp of the tooth, and my
supposition is that the fibrils have been destroyed through
all that region. In the examinations in the mouth we find
no sensation in that part in many of these cases. Gener-
ally in those slow or stationary decays that are black
throughout, if you cut into the tooth and it is still dark
in color, you will find no sensation until you reach some
point of light color.

Hyperesthesia of Dentin.

It happens in the progress of caries, in many
instances, that the normal sensitiveness becomes very
much increased. We have hyperesthesia, or hyper-
sensitiveness. There is something affecting this tissue in
the progress of decay that causes its sensitiveness to be
greatly increased. This is generally purely local and gen-
erally confined to the immediate spot, so that if you take
an excavator and at a stroke can sweep out the carious
portion of a tooth you will have removed that portion in
which the sensitiveness is most acute. When you have en-
tered the sound tissue you will find considerable diminu-
tion of sensibility ; it may be more than normally sensitive,
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