Ivory consists of an organic matrix or basis substance (which by prolonged boiling is converted into gelatin), permeated by an immense number of exceedingly fine canals. The matrix is richly impregnated with calcareous salts, which are probably held in some loose form of chemical combination with it, and is of such consistence that it retains its form after removal of the salts by an acid solvent. The canals start from the axial pulp cavity, and run in a direction generally outwards towards the periphery of the tusk; in the elephant they are of exceptional fineness, being only about - 1 -. 1 o ∙ of an inch in diameter, and are placed very closely, being separated by intervals not much greater than their own diameter. To the regularity with which the tubes are disposed, and to their small size and frequent curvature, ivory owes its fineness of grain, and probably also its almost perfect elasticity; whilst to the peculiarities of their curvatures it owes that very characteristic pattern of curved decussating lines, like engine turning, which is seen where the surface is a section transverse to the tusk. For, though it is broadly true that the tubes in elephant ivory run from the axis of the tusk to its periphery, they do not run straight, but make a succession of strong bends at regular intervals, and as the light is differently refracted by the basis substance and by the tubes according to the direction they are pursuing, this peculiarity of their course results in producing that pattern found in the dentine of Proboscidea only. Ivory differs from bone in its finer structure and greater elasticity, and in the absence of those larger canals which convey bloodvessels through the substance of bone, and appear upon it as specks or as stripes, according as it is cut transversely or longitudinally. When a transverse section of a tusk cut at a distance from the growing pulp is examined, its middle is seen to be occupied by a darkish spot of obviously different structure; this is the last remains of the pulp, rudely calcified. The outer border of the section consists of a thick layer of cementum, with which the whole tusk is coated, and the rest is ivory, showing the characteristic engine-turning pattern, and, in addition to this, numerous circular lines, concentric with the central spot. These “contour” lines are due to the occurrence of a large number of minute irregular spaces, found in all dentine, but specially abundant and disposed with a greater regularity in ivory; they are known as interglobular spaces, from the form of their boundaries when seen under a moderate magnifying power. In the areas occupied by these spaces there is a smaller proportion of lime salts and more organic matter; consequently the ivory is here less dense and more liable to decomposition, and fossil tusks, as well as the less perfectly preserved of mammoth tusks, are frequently found to have broken up into a number of superposed cones, and in transverse section to present many concentric detached rings of ivory more or less friable. See Plate VII.

Arguing from the analogy of other dentine, it cannot be doubted that the minute tubes and the interglobular spaces are not empty in living ivory, but that they contain protoplasmic substance, though how far this may have perished or altered in that portion of the tusk which is extruded and far distant from the growing pulp can only be determined by observations at present wanting. According to Von Bibra’s analyses, ivory contains as much as from 40 to 43 per cent, of organic matter, whereas human dentine contains only about 25 per cent.; of fat it contains from •24 to ’ 34 per cent. It differs from other dentines chiefly in its richness in organic constituents, in the fineness of its tubes, in their peculiarly curved course, and in the abundance of interglobular spaces arranged in “contour” lines. The tusks of the elephant are a pair of upper incisor teeth, which may attain to an enormous development. The largest teeth were possessed by the extinct mammoths, of which tusks have been found in Siberia 12 feet and more in length, and weighing 200 lb each. Holzapffel mentions one of very fine quality, that was cut up into piano keys in England, which weighed 186 lb, Among recent elephants the African species possess the largest tusks, these attaining to a length of 9 or 10 feet and a weight of 160 lb each, whilst the tusk of an Indian elephant which measured 8 feet in length and weighed 90 lb has been placed on record as exceptionally large. A pair of African tusks at the London exhibition of 1851 weighed 325 lb, and measured 8 feet 6 inches in length and. 22 inches in circumference; but authorities acquainted with the African ivory districts give 20 to 50 lb as the average weight of tusks. In Africa both males and females are furnished with large tusks; but in the Indian species a sexual difference exists, the tusks of the female projecting only a few inches from the gums, while even of the males by no means all are “tuskers.” Sanderson says that 10 per cent, of Indian male elephants have very small tusks, while in Ceylon only one in three hundred of the males is powerfully armed. The peculiarity is not always transmitted, tuskless sires (“mucknas”) breeding “tuskers,” and vice versa. The importance of tusks as giving an advantage in combat to their possessors is sufficiently indicated by the dread of a “tusker” shown by other elephants less favoured. Tusks are often broken by fighting, and always show marks of considerable wear, while even captive elephants, with their shortened tusks, make great use of them for a variety of purposes; for example, an elephant will, when set to pull at a rope, take it between his molar teeth and pass it over one of his tusks to get a good purchase. Nothing but an extremely strong and elastic material such as ivory is could withstand the strains to which it is constantly exposed.

Captive elephants have their tusks shortened, and the ends bound with metal to prevent their splitting; and, as the tusk is continually growing by the conversion of fresh portions of vascular pulp into ivory, the operation has to be repeated. When this is done at intervals of ten years, the segment cut off is valuable, and is sold as ivory; some prefer, however, to cut the tusks much more frequently. In a young elephant the vascular pulp extends beyond the portion of the tusk implanted in the jaw, while in the older animal it does not reach so far; its probable extent has to be borne in mind in shortening the tusk, as if it be encroached upon much suffering is entailed on the animal. Yet the vascular formative pulp of an elephant’s tooth is singularly tolerant of injury without having its function of ivory formation destroyed, and hence it happens that foreign bodies which have got access into the pulp chamb⅛r become solidly enclosed in ivory, The growing end of the tusk is widely open, and its edges are not much thicker than paper; the cavity which contains the pulp is of conical form, tapering to a point, which is situated at a distance down the tusk, varying, as has been before stated, with the age of the animal. The tusk grows by the conversion of successive portions of the surface of the conical mass of pulp into ivory, whilst fresh pulp is added at the flat base or open end of the tusk. The tusks are deeply implanted in curved bony sockets, which run nearly vertically upwards, so that the open growing ends of the tusks are brought up to about the level of the eyes. Hence it is not a rare occurrence for a sportsman’s bullet, intended to pierce the elephant’s brain, to penetrate the tusk near to its growing end, where the walls of the pulp cavity are quite thin, and to lodge in the “nerve” of its tooth. Indeed sportsmen remark that the forehead shot 13 less fatal to African than to Asiatic elephants, owing to the size and position of their tusks. The amount of disturbance produced by a bullet in the nerve is variable; sometimes the conversion of pulp into ivory goes on with but little interruption, so that the bullet comes to be imbedded in ivory, which fits closely up against it, instead of in pulp as it was at first. Generally the pulp immediately around it has been so disintegrated by its impact, or by subsequent inflammation, that it is incapable of conversion into normal ivory, and in its place there is a more or less irregular development of nodular secondary dentine. And sometimes there is a failure to produce even this less highly organized tissue in the immediate proximity of the bullet, which then ultimately comes to lie loose in an irregular cavity completely surrounded by secondary dentine. Of a similar nature is the so-called “abscess in ivory”; this was really an abscess in the formative pulp surrounded by a limiting membrane; as the conversion of the pulp into ivory went on, calcification passed all round the abscess and enclosed this, pus, membrane, and all, in solid ivory; and there it is discovered by the ivory cutter as an empty hole lined by a thin dried skin, the old abscess sac.

African natives sometimes spear elephants to death when they have been surrounded by an extemporized barrier of twisted creepers, and for this purpose some of them climb into trees; they also set traps made of a very heavy piece of wood shod with an iron spearhead, arranged to fall upon the elephant as he passes along a track beneath (Du Chaillu); elsewhere lances of extreme length are used in the same way. The open base of the tooth, containing the formative pulp, looking directly upwards, a spear from above intended to fall upon the head or to “pith” the animal might easily enter it, and break away, leaving the point in the tooth pulp. In a specimen now in the museum of the Odonto-logical Society, London, such a spear head remained without stopping the further growth of the tusk, and came to be solidly enclosed in ivory and secondary dentine, although it measures no less than 7∣ by 11 inches. Not a trace of its presence was discernible upon the exterior of the tusk, and it was only discovered when the tooth was sawn up. This specimen is not unique, there being said to be another, which has been turned into a cup with the imbedded spear head as its stem; and there is a specimen of a javelin head firmly built in by ivory in the museum of the Royal College of Surgeons. But that an elephant is not wholly indifferent to a large foreign body in the nerve of his tooth is proved by the fact that a notoriously fierce and dangerous “rogue” elephant in Ceylon was found when killed to have been suffering from inflammation and suppuration consequent upon the presence of a bullet in the pulp of a tooth; the supposed madness of the famed elephant of Exeter Change was also found to have been due to the pain of a diseased tooth. A common result of injury to a growing tusk is the conversion of a portion of the pulp into irregular globular masses of secondary dentine,—sometimes enclosed solidly in the midst of normal ivory, sometimes forming loose masses as big as hen eggs in the pulp cavity, and sometimes stalagmite-like appendages to its walls. Of course such deviations from normal structure seriously injure its value for industrial purposes, and they are specially apt to occur in domesticated animals vflιose tusks are being repeatedly shortened, the cut not being invariably made at a sufficient distance from the apex of the living pulp. But under no circumstances is the ivory from domesticated elephants so highly esteemed as that from the wild animal.

The large balls of secondary dentine appear on section as a conglomerate of spherical ‘masses bound together by softer and looser-textured materials; they are sometimes beautiful, but cannot be made much use of. Small spots of globular dentine sometimes occur in the midst of normal ivory, for which no cause can be detected. Malformed tusks are far from rare; the College of Surgeons possesses one about 2 feet in length, the base of which is an irregular mass of osteodentine nearly as large as a man’s head. Spiral tusks are also met with, and are almost always the result of some disease of one side of the pulp, leading to a slower growth on the one side than on the other. Much of the ivory of such tusks will be faulty; they should not be purchased except as curiosities.

The Board of Trade returns for 1879 give as the total weight of ivory imported into England during the year 9414 cwts., of the value of .£400,927 ∕ but nearly half this quantity appears again amongst the exports. By far the larger portion of the ivory is entered as coming from African ports, and less than one-fourth from India, while from this fourth a further reduction must be made in estimating the quantity produced by the country, as a considerable weight of African ivory from Zanzibar, Ac., is shipped from Bombay. About 1080 cwts. is entered as “from other countries.”

The best ivory is the African, and the first quality of that comes from near the equator; much is brought down by natives by land from the interior, whilst in other districts expeditions are organized by Europeans to go into the interior, and collect the stores gathered by native’ tribes; 20,000 lb, valued at Khartoum at £4000, would be considered a good result for a season’s expedition with one hundred and fifty men. The price of ivory varies much in different districts, being generally higher on the west than on the east coast; the transaction is generally one of barter, and the price therefore difficult to estimate. The tusks are sold by weight, and stones and iron are sometimes thrust down into the hollow pulp cavity to increase the weight, so that dealers generally feel down the hollow with an iron rod to detect foreign matter. The value of the ivory depends upon the size of the tusks; those below 6 or 7 lb weight are not worth more than half the price per lb of really fine tusks. Something depends on the care bestowed upon the tusks, which are sometimes roughly treated, while others are waxed and carefully wrapped up for protection. The African ivory trade is an ancient one, and in mediaeval times Marco Polo speaks of the traffic in ivory at Zanzibar as being astonishing in its amount.

The tusks of the mammoth from northern Siberia are said to furnish almost the whole of the ivory used by Russian ivory workers. They are found in most extraordinary abundance, and it is said that from the time of Dr Breyne’s quaint paper “Behemoth” in the Philosophical Transactions for 1737 till now there has been no intermission in the supply. They come principally from the neighbourhood of the Lena and other great rivers discharging themselves into the Arctic Ocean, and are abundantly found in the Liakhoff Islands. Mammoth tusks are slenderer, much more curved, and in proportion to the size of the animal much larger than those of recent elephants. In Siberia at different times four mammoths have been found entire, tlaeir hair, skin, and even all their soft parts having been preserved without change in the ice for countless years. Just as in some few cases all the most perishable soft parts were preserved, so in a vastly greater number the less perishable ivory was kept without change by the low temperature and exclusion of air; thus when in the summer the ice tears down portions of river banks, or floods break up frozen morasses, the tusks are brought to light. Some are in the most beautiful preservation, like recent ivory; others having been exposed before, in previous summers, their organic constituents have partly perished, and they are inclined to become broken up along the lines of interglobular space into concentric rings, or may have become so disintegrated that a fragment may be used like chalk to write with.

In England this ivory is not very highly esteemed, being considered too dry and brittle for elaborate work, and to be very liable to turn yellow. Most ivory workers strenuously deny ever using them, but, though more rarely than in former years, mammoth tusks are occasionally imported. Within the last few years an exceptionally large tusk in splendid condition was offered for sale to the Oxford University Museum at a price of £100, but was not purchased. In 1872 1630 very fine tusks were brought to England; and in 1873 1140 tusks weighing from 140 to 1601b each were imported. The best were sold at a very good price, but proved less available, even for such purposes as cutting into knife handles, than was expected, and although smaller importations arrive from time to time they can hardly be considered as a regular article of commerce, and are difficult of sale; some have been very recently sold at a price so low as ten shillings a cwt. Westendarp personally investigated the Siberian ivory trading districts, and returned with no favourable impression. He found that about 14 per cent, of the teeth were good, 17 per cent, could be made some use of, 54 were quite bad, and 15 wholly useless. The ivory looks better outside than it really is, and, as only about 30 per cent, is usable, it does not pay well for transport. He thought it not worth more than Is. 6d. a pound.

The finest quality of ivory from equatorial Africa is closer in the grain, and has less tendency to become yellow by exposure than Indian ivory. When first cut it is semi-transparent and of a warm colour; in this state it is called “green” ivory, and as it dries it becomes much lighter in colour and more opaque. This is supposed to be the result of the drying out of the “oil”; but ivory contains less than one-half per cent, of fatty material, and that which dries out is water, not oil. During this drying process the ivory shrinks considerably, so that it is necessary to season it like wood when such things as box lids, which need to fit, are to be made from it. The tusks shrink much more in their width than in their length, which will be readily understood when the many concentric rings of interglobular spaces, containing soft material, which dries up and leaves them empty, arc remembered. It is on account of this peculiarity of structure that billiard balls are turned from tusks not greatly exceeding them in diameter, for by the selection of such tusks the ivory on the opposite sides of the ball will correspond in density and in structure, and the shrinkage will be uniform about its centre. They are usually turned roughly into shape, kept for some time in a warm room to shrink, and then turned true. The thin plates cut for piano keys are dried and shrunk at once by being baked for a time in an oven, but after being dried they are still subject to changes in bulk in a moist atmosphere.

It is not always possible to judge of the quality of ivory before the tusk is cut up. The exterior, or cementum, should be smooth and polished; it is often of a deep coffee colour in the best tusks, and it should not show any large cracks. But the most profound disorganization of the ivory may exist inside an exterior which promises well, or it may be badly cracked from unequal shrinkage in drying without cracks being noticeable on its exterior. About half of the length of an average sized tusk is implanted; this will be hollow, and in a young animal the hollow will extend beyond the implanted portion; the extruded part, recognizable by the deeper colour of its cementum, is solid, and is circular or oval in section. Great care is taken by ivory cutters to cut up the tusk to the greatest advantage, its high price necessitating the strictest economy in its use. Veneers of large size have been cut by a reciprocating saw cutting a spiral shaving round the...