330 THIi MECHANICAL FUNCTIONS. 



fluid by the addition of nitrate of barytes. Iron, 

 in small quantity, is also found in the composition 

 of human bones. 



The substance which remains, after the earth has 

 been thus abstracted, retains the exact figure and 

 dimensions of the original bone, but has lost all its 

 other mechanical properties. It is soft, flexible, 

 and elastic ; resembling in every respect the mus- 

 cular or fibrous structures, and being, like them, 

 resolvible into gelatin and albumen by long boiling 

 in • ater. This substance has sometimes, but erro- 

 neously, been considered as identical with carti- 

 lage ; for it has neither the whiteness, nor the elas- 

 ticity, nor the texture of cartilage ; nor is it at all 

 similar to that substance in its chemical composi- 

 tion ; for while cartilage is formed almost wholly of 

 albumen, the animal basis of bone is almost en- 

 tirely resolvible into gelatin. 



Thus may a bone be analysed into its two con- 

 stituent parts : by the process first described we 

 obtain its earth deprived of its animal constituent ; 

 by the second, we obtain its membranous basis free 

 from earth. The first of these gives it hardness; 

 the second, tenacity : and thus, by the intimate 

 combination of these elements, two qualities, which, 

 in masses of homogeneous and unorganized matter, 

 are scarcely compatible with one another, are skil- 

 fully united. 



The mechanical structure of bone is no less 

 worthy of admiration, as evincing the skill with 

 which every part is adapted to its destined uses. 

 The animal membrane, which, as we have seen, is 

 the bed in which the calcareous phosphate is de- 

 posited, partakes of the reticular structure belong- 



