IV. 



THE STRUCTURE, COMPOSITION AND HYGIENE OF 



BONES. 



The gross structure of bones. Although the bones 

 differ very much in shape all are alike in microscopic 

 structure and in chemical coir _;tion. When alive they 

 have a bluish-white color, with a pinkish hue when blood 

 is flowing through them ; they possess considerable flexi- 

 bility and elasticity, which may be best observed in a long 

 slender bone, as a rib.* 



To get a general idea of the structure of a bone we 

 may select the humerus (Fig. 21). When fresh this is 

 closely invested on its outside by a tough membrane, the 

 periosteum, composed of .connective tissue and containing 

 many blood-vessels. On its under side new bony tissue is de- 

 posited as long as the bone is growing thicker, and through- 

 out life it is concerned in the nourishment of the bone, 



How do bones differ from one another? In what respects do all 

 bones agree? What is the color of a living bone? Name some mechan- 

 ical properties of bone. In what bones may such properties be most 

 readily seen? 



What covers a bone on the exterior? What is it composed of? 

 Does it contain bloodvessels? 



* The rib of a sheep or a rabbit when thoroughly boiled can be readily scraped 

 clean and preserved, and serves admirably to show the flexibility and elasticity of 

 bone. 



[47J 



