d teeth of the elephant--the latter, for the sake of
distinction, are termed grinders--are formed after the ordinary manner
of the teeth of animals. The organism which converts the earthy
constituents of the blood into cellular tissue and membrane,
contributes in the same way to form the teeth by the successive
deposition of layer upon layer of the soft vascular pulp. The marks of
these depositions, or laminae, are clearly distinguishable in the
longitudinal striae of the section of a tooth. Mr Corse Scott states
that the Indian elephant has only ten or twelve laminae in the tooth,
while that of the great mammoth has twenty-four, besides having a much
more regularly disposed enamel. The tooth is hollow about half-way up,
but a very small tubular cavity is visible throughout its entire
length. This, sometimes called the nerve, is in reality the apex of
successive formations in the process of growth. The grinders are
seldom used in the arts. They are of a different texture, the laminae
more loosely combined, and possessing a tendency to separate, which
renders them unfit for nearly all useful purposes. Ivory has the same
chemical constitution as ordinary teeth--that is, cartilage united to
such earthy ingredients as the phosphate of lime.

But it is very remarkable that the fossil ivory of the mammoth, and
specimens of the historic period of Pompeii or Egypt, contain
sometimes as much as 10 per cent. more of fluoride of calcium than the
ivory of the present day. We apprehend, however, that this
property--first investigated by Dr George Wilson--may be derived from
long-continued contact with earth, since fluoride of calcium is the
chief ingredient in the enamel or exterior portion of the tooth.
Ancient ivory, having thus gained in its inorganic bases, becomes
deficient in the gelatinous constituents necessary to its
preservation. We recently had a singularly beautiful application of
the knowledge of this principle in the case of the ivory specimens
sent from Nineveh by Mr Layard. On their arrival in England, it was
discovered that they were rapidly crumbling to pieces. Professor Owen
recommended that the articles should be boiled in a solution of
albumen, which was done accordingly, and the ivory rendered as firm
and solid as when it was first entombed.

We may allude here to a very singular physical property which is
possessed by the elephant's tusk. Specimens have frequently been
obtained which were found to contain mu