OSSEOUS SYSTEM. 189 



Q. What organs are most prone to take on the process 

 of ossification in advanced life? 



Jl. Those, the nutritive matter of which, is habitually 

 gelatine, as cartilage. The exception to this is the arterial 

 ossifications which so commonly take place. 



Q, How many periods are there in the development of 

 callus? 



t#. There are three; the formation of cellular granula- 

 tions, the change of these granulations to the cartilagin- 

 ous state, and the deposition of bone or calcareous sub- 

 stance. 



Q. What prevents the union of broken bones? 



/?. Such frequent motion of the ends of the broken 

 bones, as prevents the union of the parenchymas of nutri- 

 tion. 



Q. Why is union more difficult in a compound frac- 

 ture? 



/#. Because the process of suppuration wastes the nu- 

 tritive restorative matter. 



Q Of what are the teeth composed? 



\fr. Of enamel, of ordinary bone, and a cavity con- 

 taining a spongy substance, with which we are unac- 

 quainted. 



Q. What experiment proves the difference between the 

 enamel and the ordinary bony substance of the teeth ? 



.#. Diluted nitric acid, while it softens both portions, 

 whitens the enamel, and renders the osseous portion yel- 

 low. 



Q. Is the enamel an organized substance? 



*&. While it has sensibility to external impression, it 

 does not take on diseased action; it is neither absorbed 



