Ivory, the tusk or weapon of defence of the male elephant, and of which each animal has two, is placed by the chemists intermediately between bone and horn, and its mechanical characters corroborate the position. It is generally considered that the male elephant alone possesses tusks, commercially known as elephants' teeth, but this appears questionable, as by many the female is reported to have tusks likewise, but of smaller size, and some consider the latter produce the small solid tusks called "ball ivory," used for making billiard balls.

Ivory has less gelatine than bone;* but as it leaves the animal in a state fit for use, without the necessity of removing any of its component parts for its purification, its elasticity and strength arc not impaired by such abstraction. Ivory is not therefore so brittle as bone, neither does it splinter so much when broken, but its greater ultimate share of animal matter leaves it more sensible to change of form and size.

The shape of the tusk is highly favourable to its use; as it is in general solid for above half its length, and of circular or elliptical section; it is entirely free from the vessels or pores often met with in bone, and although distinctly fibrous, it cannot be torn up in filaments like horn, nor divided into thin flexible leaves as for miniatures, otherwise than by the saw.

Its substance appears very dense, and without visible pores, as if beautifully cemented by oil or wax; and notwithstanding that it possesses so large a share of lime, it admits of being worked with exquisite smoothness, and is altogether devoid of the harsh meagre character of bone. It is in all respects the most suitable material for ornamental turning, as it is capable of receiving the most delicate lines and cutting, and the most slender proportions.

* See foot note, page 118.

The general supply of ivory is obtained from the two present varieties of the animal, the Asiatic and the African: they are considered by physiologists to be distinct species, and to be unlike the extinct animal from which the Russians are said to obtain their supply of this substance; which, although described as fossil ivory, does not appear to have undergone the conversion commonly implied by the first part of the name, but to be as suitable to ordinary use as the ivory recently procured from the living species. An extract from the interesting account of "The Elephant of the Lena," is subjoined as a note.*

The hippopotamus, or river-horse, supplies the ivory used by the dentist, which is imported from the East Indies and Africa; the animal, in addition to twenty grinders, has twelve front teeth, the whole of which agree in substance with ivory, but not in their size or arrangement. The six in the upper jaw are small and placed perpendicularly; in the lower jaw of the hippopotamus, the two in the center are long, horizontal, and straight; the two next are similar but shorter; but the two external semi-circular teeth are those so highly prized by the dentists on account of their superior size, and are those usually referred to when the "sea-horse" or hippopotamus tooth is spoken of, although the animal is in reality a quadruped inhabiting rivers and marshy places.

The circular hippopotamus teeth are covered exteriorly with a thick coat of enamel, which entirely resists steel tools, and will even strike fire with that metal: it is usually removed upon the grindstone* in order to arrive at the beautiful ivory within, which, owing to the peculiarity of its section, is better adapted to the construction of artificial teeth than the purposes of turning; the other teeth are tolerably round, and tit for the lathe.

* "The Mammoth, or Elephant's bones and tusks, are found throughout Russia, and more particularly in Eastern Siberia and the Arctic marshes. The tusks are found in great quantities, and are collected for the sake of profit, being sold to the turners in the place of the living ivory of Africa, and the warmer parts of Asia, to which it is not at all inferior."

"Almost the whole of the ivory turner's work, made in Russia, is from the Siberian fossil ivory; and sometimes the tusks, having hitherto always been found in abundance, are exported from thence, being less in price than the recent. Although for a long series of years, very many thousands have been annually obtained, yet they arc still collected every year in great numbers on the banks of the larger rivers of the Russian empire, and more particularly those of farther Siberia." - The Naturalist's Library, 1836. Mammalia, Vol. v. p. 133.

The Mammoth teeth are bu rarely exposed for Bale in this country; I only learn of two; the one weighed 186 lb., was 10 feet long, of fine quality, and, except the point which was cracked, was cut into keys for pianofortes: the other also was large, but very much cracked and useless; of the latter I have a specimen: the substance of the ivory between the cracks appears quite of the ordinary character, although the interstices are filled with a dry powder resembling chalk. Both teeth were solid unto within six inches of the root.

The ivory of the hippopotamus is much harder than that of the elephant, and upwards of double the value; in colour it is of a purer white, with a slight blue cast, and is almost free from grain. The parts rejected by the dentists are used for small carved and turned works.

In texture it seems almost intermediate between the proper ivory and the pearl-shell; as when it is turned very thin, it has a slightly curdled, mottled or damasked appearance, which is very beautiful; the general substance is quite transparent, but apparently interspersed with groups of opaque fibres, like some of the minerals of the chatoyant kind.

The teeth of the walrus, sometimes called the sea-cow, which hang perpendicularly from the upper jaw, are also used by the dentists; the outer part, or the true ivory, nearly resembles the above, but the oval center has more the character of coarse bone; it is brown, and appears quite distinct. The long straight tusks of the sea-unicorn or narwal, which are spirally twisted, also yield ivory; but they are generally preserved as curiosities. These two kinds are principally obtained from the Hudson's Bay Company.