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186 THIRD PERIOD—MODERN TIMES
similar to marrow. This passage of Eustachius' book gives clear evidence
that he was well acquainted with the maxillary sinus, described a century
later by the English anatomist, Highmore, who gave it his name. The
existence of this cavity was, besides, already known before the time of
Eustachius.
The author also says that those who believe that the internal cavity of
the teeth contains marrow, and that this serves to nourish them, are
grossly deceived.
In the same chapter, Eustachius confutes an opinion, at that time gener-
ally diffused and put forward for the first time by Aristotle, viz., that
the teeth grow throughout a whole lifetime. In the senile age, he says,
the teeth become impaired still earlier than the other organs. They
become thinner by deficiency of nourishment, and, at the same time,
discolored; the incisors and canines, as they waste away, come to be also
less sharp than they were; and the molars, losing their tubercles or cups,
become levelled down and smooth. If, notwithstanding the evident
wearing out of the teeth, they seem sometimes to grow longer, this appear-
ance is not to be trusted, for it happens not unfrequently that the teeth
appear to have grown longer simply by atrophy of the gums, or also
because some humor or other morbid substance pushes them outward.
As to the sensibility of the teeth, ^ Eustachius is of the opinion that these
organs possess, besides the sensibility to pain, two other species of sensi-
bility; for, following the ideas of Galen, he also holds that the teeth
together with the tongue partake in the sense of taste; and he further
considers the disagreeable sensation known as setting on edge of the teeth,
as a species of tactile sensation peculiar to these organs.
But in which part of the tooth does the faculty of feeling reside ?
Among the authors previous to, or contemporaries of, Eustachius,
some affirmed that the sensibility of the tooth resides in the pellicle which
lines its inside cavity, others in the membrane which, like periosteum,
clothes the root of the tooth, others in both these parts. Eustachius
does not show himself more partial to the one than the other of these
opinions; he is, however, firmly persuaded that the hard substance of the
tooth is also endowed with sensibility. Though it is not easy to explain
how this may be, he considers it probable that the nerve, fraying
itself out inside of the tooth in minute filaments at the time when the
substance of the tooth is still soft and mucous, intermixes intimately
with it, thus communicating to it the faculty of feeling, which then per-
sists in it, even after the ossification of the tooth. Such an hypothesis is
certainly worthy of the lofty intellect of Eustachius, and has in itself, so
it seems to me, something of truth.
' Chap. XXV, xxvi.