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an incontestible proof of the presence of vessels, both cir-
culatory and absorbent, and consequeatly of nerves, may be
deduced from the progressive or continued growth of the m-
cisores, in the squirrel tribe, and the colouring of the teeth of
all animals from feeding on food mixed with madder, and the
subsequent loss of the acquired colour from discontinuing the
use of madder.
Mr. Fox is equally positive, and observes,* " It is very ex-
traordinary that Mr. Hunter should have considered the teeth
as devoid of internal circulation, and destitute of the living
principle. The structure of the teeth is similar to that of
any other bone, and differs only in having a covering which
is called enamel, for the exposed surface, and the bony part
being more dense. There are several parts of the body in
which we cannot by injections demonstrate the existence of
blood-vessels, of the vascularity of which no one can enter-
tain a doubt ; and as bones in general are continually receiv-
ing nourishment from the vessels which enter into their sub-
stance, it may be justly inferred, that the blood sent to the
teeth affords a similar supply, especially as a considerable
portion of animal matter enters into their composition.
A large quantity of blood is distributed to the teeth ; this
may frequently be seen in performing some operations. In
cutting off the crown of a tooth, in which the caries had not
spread to the fang, for the purpose of engrafting a new tooth,
I have several times seen a discharge of blood from the inter-
nal cavity. This blood came from the vessels of the mem-
brane in the cavity, which I have also several times seen in-
jected. Blood carries with it the basis of nutrition, and is
sent to those parts only where renovation is necessary. For
what other reason then, but to impart some principle of nu-

Fox, History of the Teeth, pages 33, 34.