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238 THIRD PERIOD—MODERN TIMES
DoMENico Gagliardi, professoF of anatomy and of medicine at Rome,
published an excellent work on the anatomy of the bones/ in which he
occupies himself not only with the structure of bones, properly so called,
but also with that of the teeth. He considers the enamel to be formed
bv parallel and contiguous fibers, coated, so to speak, by a concreted
juice, sui generis, which acquires a much greater consistence than that
of the bones. Gagliardi says that by rubbing teeth hard together, or
striking them with a steel, he was able to extract sparks from them."^
Jean Duverney (1648 to 1730), a celebrated French anatomist,
wrote a good monograph"* about the teeth. As different anatomists of
the sixteenth century had already done, he examined many fetal jaws
in order to study in them the formation of the teeth. In relating his
observations, he says that he found in every alveolus a mass of soft viscous
matter, having the form of the tooth that is to derive from it, and which
may be considered as its nucleus. This nucleus is entirely surrounded
by a membrane, which the author likens to that which surrounds the
fetus, and to which he gives the name of choroid membrane. From the
surface of the nucleus a gelatinous juice transpires, which, thickening
in layers, forms the enamel and the rest of the tooth. The choroid
membrane is abundantly furnished with nerves, and with blood and
lymph vessels. Into the interior of the teeth penetrate vascular and
nervous branches which serve to maintain its vitality. In fetal jaws one
finds, besides the germs of the deciduous teeth, also those of the permanent
ones. The "choroid membrane" does not follow the tooth when it
issues from the alveolus; it remains instead within the latter, forming
the peridental membrane.
Duverney says that in old people the root cavity diminishes in so con-
siderable a manner, and the vessels are so compressed that they almost
entirely disappear. It is then that a period of decadence begins in the
tooth, it is more feebly nourished, wears away more rapidly than hitherto,
and becomes shorter.
The author also speaks of senile atrophy of the jaws, especially of the
alveolar processes. With regard to this, he observes that if in old age
the lower jaw advances beyond the upper, this depends wholly on the
disappearance of the alveolar border, which projected more in the upper
than in the lower one.
Duverney admits the existence of direct vascular relation between the
gums and the teeth; because in the case of diseases of the gums it is rare
not to find the teeth altered as well.
P rom the point of view of the development and nutrition of the teeth,

' Anaronif f).ssiiim, Roni;c, 1689. - Portal, vol. iv, p. iii; Blantlin, p. 28.
'jean (Iiiichard Diivtiiny, Memoire sur les (kiits, Paris, 1689.