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body of the tooth, is destroyed when the tooth has risen lo
its proper height.
De La Sonne,* and other physiologists, attempt to assign a
cause why the teeth rise and pass through the gum, by say-
ing that as roots are added, the bodies of the teeth are push-
ed or forced up through the gum, this being softer than the
bottom of the sockets. But when we come to consider the
appearance of the permanent teeth, we shall be fully sensi-
ble how inadequate such a theory is.
It has been mentioned by most authors, who have written
on dentition, that the membrane which surrounds the body
of a tooth is stretched, bruised, and even lacerated by the
increased size of the tooth. Dr. Underwood supposes it to
be strong and nervous, and adds, " The most painful part of
dentition, and that in which children are most exposed to con-
vulsions, is usually from the teeth cutting through the perios-
teum, (or nervous membrane mentioned above,) that covers
the teeth." Van Swieten although he did not believe the
temporary teeth had roots, says, " These rudiments of the
teeth are placed in the sockets of the jaws ; but the opening
from each of these sockets, is covered by a thick coriaceous
membrane, which must be bruised, or even torn by the tooth
in bursting out, so that after the tooth had burst out, the rag-
ged edges of this membrane have been observed by the ac-
curate Herissant. These edges becoming dry fall away
spontaneously. Therefore the tooth in endeavouring to
make its way out, must exert a considerable force in order
to break through this membrane."!
It appears rather strange that Van Swieten could imagine
that the temporary teeth, which in another part of his work,

* Acad des Scien, in 4to. L'an. 1752. Mem. p, 168.
t Comment. Vol. xiv. page 743.