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of the odontoblasts. For instance, take this illustration,
the odontoblasts being here (indicating), the fibril is pro-
jected through the dentinal tubule to the dento-enamel junc-
tion and this fibril is a prolongation of the substance of the,
odontoblast, a part of the cell. The odontoblasts are in
physiological relation with the nerves of the pulp, and when-
ever you touch one of those fibrils you have in effect touched
one of the odontoblasts and the sensation is conveyed to the
• • •
sensonum. This, it strikes me, is the proper explanation
of the sensitiveness of dentin. We do not need nerves in
the dentin in order that it may be sensitive. The element
of the cell projected into the dentin is the sensitive element,
and the nerves being in physiological relation with the
odontoblasts place them in connection with the central
ganglia through the conveyance of sensation by these nerves.
Then we should expect, if we should cut into a tooth and
it was not sensitive, that there was something wrong with
that tooth, or if we should cut into our finger and find it
not sensitive we would think that there was something wrong
with our finger.
Destruction of the Dentinal Fibrils in Caries.

Where and how are the dentinal fibrils destroyed during
the progress of caries? Now, this subject is one which seems
to have escaped laboratory demonstration, and for the pres-
ent we will have to depend upon the best interpretation we
can make of clinical observations that have come to us.
We find that anywhere in the hyaline zone of Tomes the
softened material is sensitive. You will find sensation be-
fore you have removed all of the softened material from a
tooth, and in that softened material you will usually find
the greatest sensitiveness, whether the case is one of hyper-
sensitiveness or not. A certain amount of sensitiveness we
always expect to find in living teeth. The greatest degree
of sensitiveness is at the dento-enamel junction in teeth that
are in an ordinary state of health. After passing deeper into
the tooth the sensitiveness is not so great. This coincides
precisely with the fact that we find the greatest degree of
sensation in the skin, and when we pass to the deeper parts
beyond the skin the degree of sensitiveness is not so great.
Hence, we find that this corresponds with conditions found
elsewhere in the body. Now, in the case of caries we find
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