46 PHYSIOLOGY. 



of earthy and animal matter, the former constituting about 

 two-thirds, the remaining! one-third being animal matterl 

 As we find portions of both these substances in the minutest 

 particles of bones, both are therefore considered essential to 

 its composition, and existing in a state of chemical union, 

 and not as a mere mechanical mixture. These two sub- 

 stances can be readily separated from each other. ' If we 

 immerse bones for some time in diluted nitric acid, or muri- 

 atic acid, though they retain their size and form, their 

 weight is considerably diminished, and they are rendered 

 soft, pliable, and elastic. The earthy portion, phosphate of 

 lime, has been dissolved, and is held in solution in the fluid, 

 and the animal portion, gelatine, remains uninjured^ 



Membranous, or gelatinous portion of bone ; the earthy portion being 

 so completely removed, that it is capable of being tied in a knot. 



19. If bones are subjected to a strong heat, as in a char- 

 coal fire, on cooling they appear to have undergone no alter- 

 ation in figure or bulk ; but they are rendered white as 

 chalk ; their weight is lessened, and they become very 

 brittle. In this case, the animal matter has been wholly 

 consumed by the fire, while the earthy part remains un- 

 changed ; in the former case, the very reverse happened ; 

 the animal matter remaining, and the earthy being removed. 



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