80 EOXE. 



movealjly together, serve also as levers for executing the movements of 

 the body. 



While substantially consisting of hard matter, bones in the living 

 body are covered with periosteum and filled with marrow ; they are 

 also pervaded by vessels for their nutrition. 



Physical Properties of Bone. — Cone has a white colour, with a 

 pink and slightly bluish tint in the living body. Its hardness is well 

 known, but it also possesses a certain degree of toughness and elasticity ; 

 the last property is peculiarly well marked in the ribs. Its specific 

 gravity is from 1"87 to 1"97. 



Chemical Composition. — Bone consists of an earthy and an animal 

 part, intimately combined together; the former gives hardness and 

 rigidity, the latter tenacity, to the osseous tissue. 



The earthy part may be obtained separate by calcination. Wlien 

 bones are burned in an open fire, they first become quite black, like a 

 piece of burnt wood, from tlie charring of their animal matter ; but if 

 the fire be continued with free access of air, this matter is entirely 

 consumed, and they are reduced to a white, brittle, chalk-like sub- 

 stance, still preserving their original shape, but with the loss of about 

 a third of their weight. The earthy constituent, therefore, amounts to 

 about two-thirds of the weight of the bone. It consists principally of 

 phosphate of lime, Avith about a fifth part of carbonate of lime, and 

 much smaller proportions of fluoride of calcium, chloride of sodium, 

 and magnesian salts. 



The animal constituent may be freed from the earthy, by steeping a 

 bone in diluted hydrochloric acid. By this process the salts of lime 

 are dissolved out, and a tough flexible substance remains, which, like 

 the earthy part, retains the perfect figure of the original bone in its 

 minutest details ; so that the two are evidently combined in the most 

 intimate manner. The animal part is often named the cartilage of 

 bone, but improperly, for it differs entirely from cartilage in structure, 

 as well as in physical pro])erties and chemical nature. It is much 

 softer and much more flexible, and by boiling it is almost wholly 

 resolved into gelatin. It may accordingly be extracted from bones, in 

 form of a jelly, by boiling them for a considerable time, especially 

 under high pressure. 



The earthy or saline matter of bone, as already stated, constitutes aboiit two- 

 thirds or fiG"? per cent., and the animal part one-third, or olV:! jier cent. ; but from 

 observations made on animals, it ajipears that the proportion of the several con- 

 stituents may differ somewhat in different individuals of the same species lender 

 api>arently similar conditions. The proportion of earthy matter appears to 

 increase for some time after Ijirtli, and is considerably greater in adults than in 

 infants ; but. from the varying conditions of individuals as to health and nutri- 

 tion in after life, there is as yet no thoroughly comparable series of experiments 

 to detennine whether any constant difference exists in old age. IMoreover, it is 

 not clearly established that the differences observed depend on the composition of 

 the proper osseous substance ; for the larger proportion of animal matter in 

 infancy may l)e due to the greater vascularity of infantile bones and the difficulty 

 of thoroughly removing the vessels from their pores. The spongy osseous tissue, 

 carefully freed from fat and adhering membranous matter, has been found to 

 contain rather less earth than the compact substance : and, in accordance with 

 this result, differences, although on the whole insignificant, have been found in 

 different bones of the skeleton, apiiarently de])ending on the relative amount of 

 their compact and spongy tissue. (Kees, Von Bibra, Alphonse IMilne-Edwards.) 

 Here again it remains to be shown that the result is not due to differences in the 



