Page:The American Cyclopædia (1879) Volume III.djvu/64

58 BONE crumbling to pieces at the least touch. To the earthy part, which consists principally of phos- phate and carbonate of lime, 51 per cent, of the former and 11 per cent, of the latter, the bone owes its hardness, density, rigidness, and white color; to the animal part, princi- pally cartilage, or some form of gelatine, about 32 per cent., it owes its strength of cohesion. These proportions vary at different ages : in the child, the animal matter forms nearly one half of the bone, accounting for its greater flexibility and the less liability to fracture at this age ; in the old, the earthy matter is about 84 per cent., explaining the great brittleness and easy fracture of the bones in aged persons. In the disease called rickets, common among the ill-fed children of the poor in Europe, but somewhat rare in America, there is a de- ficiency in the deposit of earthy matter, ren- dering the bones so flexible that they may be bent almost like wax. The power of bone to resist decomposition is remarkable : fossil hones deposited in the ground before the ap- pearance of man upon the earth have been found by Cnvier exhibiting a considerable cartilaginous portion ; the jaw of the Cam- bridge mastodon was found by Dr. 0. T. Jack- son to contain 42'6 per cent, of animal matter, and cartilage obtained from the same specimen by means of dilute acid was readily converted into gelatine, and made a good glue ; a portion of one of the vertebral spines of Dr. J. C. War- ren's mastodon was found to contain SO per cent, of animal matter. The chemical consti- tution of bone is shown in the following anal- yses by Berzelius and Marchand : 1. Organic or animal matter 33-80 33-25 fPhosphate of lime 51-04 52-26 Carbonate oflime 11-80 10-21 2. Inorganic Fluoride of calcium 2-00 TOO or earthy -| Phosphate of magnesia 1-16 1-05 constituents. | Soda and chloride of sodium 1-20 1-17 Oxide of iron and manganese, and loss 10-5 100-00 100-00 Some recent authorities deny the existence of fluoride of calcium in bone. Bones are not solid. Make a section of almost any bone, and two kinds of structure are seen: one dense, firm, and compact, on the exterior surface ; the other loose, spongy, enclosing cells or spaces communicating freely with each other, in the interior of the bone, and surrounded by the more compact tissue. The loose structure abounds in the ends of bones, securing at the same time greater lightness and sufficient ex- pansion to form the joints, while in the shaft or central portion, where strength is most needed, the compact tissue is more developed. Bones are of different forms, according to the uses to which they are to be applied: some are long, as in the limbs, and these are the principal levers of the body ; others are flat and thin, composed of two layers of compact tissue, with an intervening cellular structure, destined to enclose cavities. Bones have also a variety of eminences and depressions, for the attachment of muscles, the protection of nerves and vessels, &c. ; these eminences, or processes, are well marked in proportion to the muscularity of the subject. In females and feeble men the bones are light, thin, and smooth, while in the powerfully muscular frame the bone is dense and heavy, and every prominence is well developed. Exercise is as necessary to the strength of a bone as it is to the strength of a muscle ; if a limb bo disused from paralysis, or the body be prostrated by long disease, the bones waste as well as the soft parts. The external surface is perforated by numerous minute openings, which transmit the arteries and veins to the interior ; this sur- face is covered by a firm tough membrane, the periosteum, composed of densely interwoven white fibrous tissue. The cells, or cancelli, of the spongy portions of bone, are made up of thin and inosculating plates of osseous tissue, enclosing spaces between them which are filled with marrow or medulla; these are lined with a delicate membrane. On a superficial observa- tion it appears as if the plates of the cancel- lated structure were arranged without definite plan ; but the researches of Prof. Jeffries Wy- man and others show that the cancel!! of such bones as aid in supporting the weight of the body are arranged either in the direction of that weight, or in such a manner as to support and brace those cancelli which are in that direction. The 'arrangement of these bony plates in the lumbar vertebra, the neck of the thigh bone, the tibia, and the ankle and heel, is of itself enough to indicate that man, alone of animals, naturally assumes an erect position. This relation is most evident in the above- mentioned bones, and in the adult, it being less observable in youth and old age. There is no real difference between the compact and the spongy structure of bone, the degree of condensation being the only distinction. The cells of the cancelli communicate freely with each other. In the long bones the marrow is not contained in cells, but in one central med- ullary canal, lined by a membrane. Both the periosteum and the medullary membrane are abundantly supplied with blood vessels, and are therefore intimately connected with the nutrition of the bone, and their destruction to any great extent leads to the death of the part in contact with them. Microscopic ex- amination can alone explain the intimate struc- ture of bone. If a thin transverse section of a long bone, as the femur, he examined un- der the microscope, the compact tissue will present several dark circular or oval spots, surrounded by numerous concentric lines ; in these lines will be perceived minute black spots, with other lines leading from them in various directions. The larger oval or circular spots are the openings of vascular canals, called "Haversian," from their discoverer, Clopton Havers; these canals are numerous, taking a course parallel to the axis of the bone, joined together by free inosculation of short trans-