IVORY 1037 



slabs. By many geologists it is regarded as a metamorphic sandstone. It derives 

 its name from Mount Itacohimi, in Brazil. Diamonds have occasionally been found 

 imbedded in itacolumite; and it has been supposed that some connection exists 

 between the distribution of this rock and the occurrence of diamonds. 



IVORY. (Ivoire, Fr. ; Elfenbein, Ger.) The osseous matter of the tusks and 

 teeth of the elephant, and of the tusks of the hippopotamus, and the horn of the 

 narwhal. 



Formerly, the name ivory was given to the main substance of the teeth of all 

 animals ; but it is now, by the best anatomists and physiologists, restricted to that 

 modification of dentine, or tooth-substance, which, in transverse sections or fractures, 

 shows lines of different colours, or striae, proceeding in the arc of a circle, and forming 

 by their decussation minute or curvilinear lozenge-shaped spaces. By this character, 

 which is presented by even the smallest portion of an elephant's tusk, in transverse 

 section or fracture, true ivory may bo distinguished from every other kind of tooth- 

 substance, and from every counterfeit, whether derived from tooth or bone. It is a 

 character this engine-turned decussatory appearance which is as characteristic of 

 fossil as of recent ivory. Although, however, no other teeth except those of the 

 elephant present the characteristics of true ivory, there are teeth in many other species 

 of animals which, from their large size, and the density of their principal substance, 

 are useful in the* arts for purposes analogous to those for which true ivory is used ; 

 and some of those dental tissues, such as those of the large tusks of the hippopotamus, 

 are more serviceable for certain purposes, especially in the manufacture of artificial 

 teeth by the dentist, than any other kind of tooth-substance. The utility of teeth in 

 commerce and in the arts, depends chiefly on a peculiar modification in their laws 

 of growth. For the most part teeth, as in our own frames, having attained a certain 

 size and shape, cease to grow. They are incapable of renewing the waste to which 

 they are liable through daily use, and when worn away, or affected by decay, they 

 perish. Teeth of this kind are said to be of limited growth ; but there are other 

 teeth, such as the front teeth of the rat, rabbit, and all the rodent tribe, the tusks of 

 the boar and hippopotamus, the long descending canine tusks of the walrus, the still 

 longer spiral horn-like tusk of the narwhal, and the ivory tusks of the elephant, which 

 are endowed with the property of perpetual growth ; that is, they grow as long as the 

 animal lives. 



' In teeth of unlimited growth, fresh pulp, fresh capsule, and in some instances also 

 fresh enamel organs are formed, and added to the pre-existing constituents of the 

 tooth matrix, in proportion as those are calcified or converted into tooth-substance ; 

 and as fast as the ivory and enamel may be worn away from the summit of such a 

 tooth, will ivory and enamel be formed at its base, and thus the growth of the tooth 

 is uninterrupted. The ratio of the addition of the formative principles is at first 

 greater than the ratio of abrasion, and the tooth not only grows, but increases in size. 

 When, however, the animal has attained its full growth, the tooth, for the most part, 

 is reproduced without increase of size, or, at most, augments only in length, and that 

 in cases where its summit is not perpetually worn down by being opposed to that of 

 an opposite tooth.' 



With respect to the distribution of the elephant, the same authority (Professor Owen) 

 has the following remarks : 



' In the present creation, elephants are restricted to the African and Asiatic con- 

 tinents. The African elephant, as is well known, is a distinct species from the 

 Asiatic one ; and some of the Asiatic elephants of the larger islands of the Indian 

 Archipelago, as those of Sumatra, if not specifically distinct from the elephants of 

 Continental Asia, form, at all events, a strongly marked variety. With reference, 

 however, to the commercial relations of ivory, it is chiefly worthy of notice that in 

 the Asiatic elephants, tusks of a size which gives them the value of ivory in com- 

 merce are peculiar to the males, whilst in the African elephants both males and 

 females afford good-sized tusks, although there is a sexual difference of size in this 

 species, those of the males being the largest. In former times, and, as it would seem, 

 before man existed to avail himself of this beautiful animal substance for use or 

 ornament, the large animals furnishing true ivory, proboscidian quadrupeds, as they 

 ore termed, from their peculiar prehensile nasal appendage, were much more widely 

 spread over the globe, and existed in far greater numbers than in the present day, 

 more numerous in individuals, more numerous in species, manifesting so great di- 

 versities in the conformation of their grinding teeth, as to have led the naturalist 

 and the palaeontologist to divide them into two genera, called Elephas and Mastodon. 

 A true elephant roamed in countless herds over the temperate and northern parts of 

 Europe, Asia, and America. This was the creature called by the Russians Mammoth ; 

 it was warmly clad with both hair and fur, as became an animal deriving sustenance 

 from the leaves and branches of trees, which grow as high as the 65th degree of north 



