BONE. By bones are meant those hard, solid, well-known substances, to which the firmness, shape, and strength of ani mal bodies are owing ; which, in the lar ger animals, form, as it were, the ground work upon which all the rest is built. In man, in quadrupeds, and many other ani mals, the hones are situated below the other parts, and scarcely any of them are exposed to view ; but shell-fish and snails have a hard covering on the outside of their bodies, evidently intended for de fence.
The bones are the most solid part of animals. Their texture is sometimes dense, at other times cellular and porous, according to the situation of the bone. They are white, of a lamellar structure, and not flexible nor softened by beat. Their specific gravity differs in different parts. That of adult's teeth is 2.27: the specific gravity of children's teeth is 2.08. It must have been always known that bones are combustible, and that, when sufficiently burnt, they leave behind them a white porous substance, which is taste less, absorbs water, and has the form of the original bone. The nature of this substance embarrassed the earlier che mists. But in 1771, Scheele mentioned, in his dissertation on fluor spar, that the earthy part of bones is phosphate of lime. This discovery was the first and the great step towards a chemical know ledge of the composition of bones. The component parts of bones are chiefly four; namely, the earthy salts, fat, gelatine, and cartilage. The earthy salts may be ob tained, either by calcining the bone to whiteness, or by steeping it for a sufficient length of time in acids. In the first case, the salts remain in the state of a brittle white substance ; in the second, they are dissolved, and .may be thrown down by the proper precipitants. These earthy salts are four in number : 1. Phosphate of lime, which constitutes by far the greatest part of the whole. 2. Carbonate of lime. 3. Phosphate of magnesia, lately discovered by Fourcroy and Vauquelin. It occurs in the bones of all the inferior animals examined by these indefatigable chemists, but could not be detected in human bones. 4. Sulphate of lime, de
tected by Mr. Hatchett in a very minute proportion. The proportion of fat con tained in bones is various. By breaking bones in small pieces, and boiling them for some time in water, Mr. Proust obtain ed their fat swimming on the surface of the liquid. It weighed, he says, one fourth of the weight of the bones employ ed. This proportion appears excessive, and can scarcely be accounted for, without supposing that the fat still retained water. The gelatine is separated by the same means as the fat, by breaking the bones in pieces, and boiling them long enough in water. The water dissolves the gelatine, and gelatinizes when sufficiently concen trated Hence the importance of bones in making portable soups, the basis of which is concrete gelatine, and likewise in making glue. When bones are de prived of their gelatine by boiling them in water, and of their earthy salts by steep ing them in diluted acids, there remains a soft white elastic substance, possessing the figure of the bones, and known by the name of cartilage. From the experiments of Hatehett, it appears that this substance has the properties of coagulated albumen. This cartilaginous substance is the por tion of the bone first formed. Hence the softness of these parts at first. The phosphate of lime is afterwards gradually deposited, and gives the bone the requi site firmness. The gelatine and fat, es pecially the first, give the bone the re quisite degree of toughness and strength ; for when they are removed, the bone be comes brittle. The relative proportion of phosphate of lime and cartilage differ ex ceedingly in different bones and in differ ent animals Ox bones, according to the analysis of Fourcroy and Vauquelin, are composed of Solid gelatine . . . . 51 Phosphate of lime . . . 37.7 Carbonate of lime . . . 10 Phosphate of magnesia • 1.3 100.0 See ANATOMY.