BONES. 507 



bone. When dried it shrinks together somewhat, be- 

 comes hard and brittle, but remains translucent. By 

 boiling with water it is dissolved, forming glutin. 



"Water, heated above 100, i. e. under high pressure, 

 extracts all the cartilage from bone, dissolved as gela- 

 tin, leaving the pure earthy matter behind. 



When bones are burned with access of air, the 

 organic ingredients are destroyed, and the earthy 

 matter remains behind as a white substance, having 

 the form of the bone. It consists of neutral calcium 

 phosphate mixed with calcium carbonate, in varying 

 quantities in different animals ; and small quantities of 

 magnesium phosphate and calcium fluoride. Calcium 

 carbonate is contained, as such, in the living bone. 

 Whether bony substance is a chemical compound of 

 cartilage with calcium phosphate, or is merely a mix- 

 ture, is undetermined. The facility with which the 

 two constituents can be separated, however, without 

 necessitating a change in the form of the bone, speaks 

 for the latter view. 



The amount of organic and earthy matter contained 

 in bones, estimated by calcining the bones, is found 

 to vary somewhat in bones of different parts of the 

 body, of different age, and in the bones of different 

 classes of animals. In the parietal bone of man, for 

 example, 68.3 per cent., in the sternum 64.7 per cent., 

 in the tibia 65.5 per cent, of earthy matter have been 

 found. Human bones, thoroughly dried, contain over 

 8 per cent, of calcium carbonate. The average amount 

 of calcium phosphate is 57 per cent., that of earthy 

 matter 33 per cent. The bones of all mammalia are 

 very similar in their composition to those of man ; 

 those of birds, however, are much richer in inorganic 

 ingredients. In the femur of the pigeon, for example, 

 89 per cent, of earthy matter was found, of which 82 

 per cent, consisted of calcium phosphate. In the bones 

 of amphibious animals and fish, on the contrary, the 

 amount of organic matter is decidedly greater. 



Fish scales have a composition similar to that of 

 bones, only containing more organic matter. This 

 does not, however, differ in its chemical composition 



