202 NUTRITION OF BONE. 



while the bony matter is depositing, a process of no less 

 importance is also going forward. The cartilage is ob- 

 sorbed too, not merely where the bony matter is deposit- 

 ed, but so as to leave the necessary cells, cavities and 

 holes, which are to exist in the future bone. 



In the union of broken bones, we find a strong con- 

 firmation of what has been said on the formation of bone. 

 When a bone is fractured, there is soon poured out from 

 the vessels of its divided extremities, a soft, fluid matter 

 chiefly the coagulating; portions of the blood ; this 

 gradually becomes cartilage, vessels containing red blood 

 appear in it, bony matter is deposited, and finally a ring 

 of bone completely surrounds the broken extremities, 

 and cements them together more firmly than before the 

 fracture. It is not necessary that the ends of the bones 

 should be placed in direct apposition, that union may be 

 produced. Cases frequently occur, where, by bad man- 

 agement on the part of the surgeon, the broken ends 

 slip by each other, and are not restored to their proper 

 position. Here they are connected by a bridge of bone, 

 which is made between the overlapping extremities, unit- 

 ing them firmly to each other. 



Emily. What a curious and admirable system of 

 means truly, does this account of the formation of bone 

 unfold 1 



Dr. B. The wonder does not cease here, for the 

 process of the preservation and nutrition of bone is 

 equally curious with that ofits formation. 



Emily. What is the necessity of nutrition ? When 

 once formed, will not a bone continue for life ? 



Dr. B. Certainly not ; you forget that bones must 

 grow with the growth, and strengthen with the strength 

 of the body ; that they are always composed in part of 

 living matter, and consequently subject to continual 

 change. As in the other parts, so in the bones, each 

 particle after a time becomes unfit for the purposes for 

 which it was originally deposited, is taken away, and 

 new ones supply their places. The fact of this constant 



