BONE. Ixxxix 



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. When bones 

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

 burnt wood, from the 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 substance, still preserving their 

 original shape, but with the loss of about a third of their weight. The 

 earthy constituent, therefore, amounts to about t>vo-thirds of the weight of 

 the bone. It consists principally of phosphate of lime, with 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 acul. By this process the salts of lime are dissolved 

 out, and a tough, flexible substance remain*, 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 properties 

 and chemical nature. It h much softer and mujh 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 about two-thirds 

 or 667 per cent., and the animal part one-third, or 33'3 per cent. ; but from observa- 

 tions made on animals, it appears that the proportion of the several constituents may 

 differ somewhat in different individuals of the same species under apparently similar 

 conditions. The proportion of earthy matter appears to increase for some time after 

 birth, and is considerably greater in adults than in infants ; but, from the varying 

 conditions of individuals as to health and nutrition in after life, there is as yet no 

 thoroughly comparable series of experiments to determine whether any constant 

 difference exists in old age. Moreover, it is not clearly established that the differ- 

 ences observed depend on the composition of the proper osseous substance ; for the 

 larger proportion of animal matter in infancy may be 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, apparently depending on the relative 

 amount of their compact and spongy tissue. (Rees, Von Bibra, Alphonse Milne- 

 Edwards.) Here again it remains to be shown that the result is not due to differences 

 in the proportion of minute pores and lacunae, which contain soft matter scarcely 

 separable in such experiments. 



Subjoined are the statements of two analyses. The one, by Berzelius, is well 

 known; the other, which nearly agrees with it, was performed by Mr. Middleton, in 

 the laboratory of University College.* 



Berzelius. Middleton. 



Animal matter 33 30 3343 



Phosphate of lime 51-04 51'11 



Carbonate of lime 11-30 10-31 



Fluoride of calcium 2-001-99 



Magnesia, wholly or partially in the state of phosphate . 1*16 1'67 

 Soda and chloride of sodium V20 1-68 



* Philosophical Magazine, vol. xxv. p. 18. 



