IMPORTANT FOODSTUFFS, IMPORTANT TISSUES 121 



Bones and Teeth. The bones and teeth, which form the 

 solid structural portions of the body are composed of both or- 

 ganic and inorganic material. The bones are living tissue, and 

 their cells wear out and are repaired just as any other cells. 

 About 60% of bone tissue is organic material, largely the protein 

 collagen. There also is some mucoid, osseomucoid. In the hol- 

 low bones marrow is found, and this material contains much fat. 

 There are two kinds of marrow, yellow and red, the red con- 

 taining many red corpuscles. In the bones extensive amounts 

 of inorganic material are found, chiefly calcium phosphate and 

 carbonate. 



The teeth are composed of three materials, enamel, dentine, 

 and cement. The enamel is the hardest substance in the body 

 and contains only about .5% of water and about 91% of calcium 

 phosphate. Dentine and cement are of about the same composi- 

 tion as bone. 



Cartilage contains collagen, chondroalbuminoid, salts and 

 mucoid. 



Connective Tissue. There are two chief types of connective 

 tissue, yellow and white. The white elastic tissue consists 

 mainly of collagen, the yellow of elastin. Both forms contain 

 mucoid and extractives. 



The Blood. Many points in connection with the blood have 

 been considered elsewhere, chiefly in the discussion of hemo- 

 globin in the chapter on proteins. Some additional points 

 will be considered here. The blood is a fluid in which a variety 

 of formed elements, corpuscles and platelets, are suspended. It 

 is of the utmost importance as a circulating medium for it car- 

 ries oxygen, C0 2 , food materials, products of internal secretion, 

 various waste substances, heat, salts, etc., to or from the cells. 

 The blood is thus the common carrier of the body, delivering 

 fuel and other supplies to the cells, and carrying away the 

 cell refuse. Each cell is bathed in an aqueous fluid just as 

 were the original independent unicellular organisms which 

 lived in the sea. 



The general composition of the blood is as follows (from 

 Ma thews) : 



