262 



ADVANCED PHYSIOLOGY 



During a period when a bone is being repaired it must be 

 kept perfectly quiet, for any movement would easily tear 

 apart the newly made materials. Consequently, the surgeon 

 always binds broken bones in such a way as to prevent motion 

 of the parts until they are well knit together. The setting oj 

 a bone by a surgeon consists simply in bringing the two broken 

 ends nicely together and then binding them in proper position. 

 Since the animal matter in the bones of children is so much 

 more abundant than it is in adults, it follows that broken 

 bones are more easily mended in childhood than in later life. 

 In more advanced years when the amount of animal matter 

 is further decreased, the bones grow more brittle and are more 

 easily broken. At the same time they are not so easily re- 

 paired, because of the scarcity of living bone cells. 



Microscopic Structure of Bone Tissue. Figure 133 shows 

 a very thin piece of bone highly magnified. 1 It consists of 



FIG. 133. SECTIONS THROUGH BONE 



A, cross section; B, longitudinal section. Canaliculi are the minute canals radiating 

 from the elongate, black areas (lacunae). Lamellae are not shown. 



groups of concentric rings, arranged around small openings. 

 These openings indicate the places where canals, running 



