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THE SIXTEKSTIl CENTURY 185

of experiencing pain acconipanitd In a feeling of pulsation (a fact alrcacK
mentioned h\ Galen), because a nerve and an arrer\ penetrate into it.
In the ox the penetration of bloodvessels into the roots of the teeth can
be more readih ascertained than in man. It may be admitted that the
same occurs in the human teeth; and this, for the reasons alread\ lmncu,
and also because onl\ b\ admitting the existence of an artery within the
cavity of the tooth can be explained the copious flow of florid red blood
from a decayed tooth, which has, in some cases, been known to imperil
the lite of a patient. And I myself, says Eustachius, have observed
with my own e\'es an accident of this kind.
The author then passes on to speak of the eruption of the teeth,' but
the data with which he furnishes us are neither ver\' precise nor very
exact.
Eustachius, without declaring himself for or against it, cites, in this
chapter, the opinion of those who believe in the possibilit\ of a third
dentition in old people. He returns to this subject in the last chapter
but one ot his book, which treats of dental anomalies: "Ali," says he,
"testifies to old persons having had all their teeth renewed. This has
been derided as chimerical by medical men of later date, or at least only
admitted under the condition that such teeth be of a nature completeh
different from the first."
Our teeth, says the author, grow old together with us, and toward
the term of life they abandon us, a fact which also distinguishes them
from the other bones. When, however, it occurs, through illness, that
the teeth are extracted or fall out spontaneously before the period of
old age, the alveoli become filled up with a bony substance; and in addi-
tion the tw^o osseous scales of the maxillary bones approach one another
and unite together in such a manner as to form a sharp margin, every
vestige of a cavity being obliterated.
Speaking of the nutrition and growth of the teeth,- Eustachius says
that—given the existence of the dental nerves and bloodvessels— it is
not difficult to explain how the teeth are nourished, grow, live, and feel.
He therefore rejects the opinion of those who held that the teeth of the
lower jaw derived their nourishment from the marrow contained within
this bone, and that those of the upper jaw received it from a humorous
substance similar to marrow, existing in the large cavit\- of the upper
maxillary bone. Against the supporters of this opinion Eustachius
raises, among others, the following objections, viz., that the marrow of
the inferior jaw does not in an\- wa\ touch the teeth, so that such a mode
of nourishment cannot be imagined, and that it is completely erroneous
that the large cavity of the upper maxillary bone contains a humor

- Chap,
' Chap, xxii, p. 65. xxiii, p. 70.