370 THE MECHANICAL FUNCTIONS. 



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 muscular or fibrous structures, and 

 being, like them, resolvable into gelatin and 

 albumen by long boiling in water. This sub- 

 stance has sometimes, but erroneously, been 

 considered as identical with cartilage ; for it has 

 neither the whiteness, nor the elasticity, nor the 

 texture of cartilage, nor is it at all similar to 

 that substance in its chemical composition : for 

 while cartilage is formed almost wholly of albu- 

 men, the animal basis of bone is almost entirely 

 resolvable into gelatin. 



Thus may a bone be analysed into its two 

 constituent parts : by the process first described 

 we obtain its earth deprived of its animal con- 

 stituent; by the second, we obtain its mem- 

 branous 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 ho- 

 mogeneous and unorganized matter, are scarcely 

 compatible with one another, are skilfully 

 united. 



The mechanical structure of bone is no less 



