IMPORTANT FOODSTUFFS, IMPORTANT TISSUES 139 



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. 



Dentine contains 26-28% of organic material. This yields 

 gelatine on boiling, but it is considered to be not identical with 

 collagen. Cement is practically identical with bone in compo- 

 sition. Bone ash has approximately the following composition: 

 Calcium phosphate 87%, calcium carbonate 10%, calcium chlor- 

 ide 0.2%, calcium fluoride 0.35%, magnesium phosphate 1.6%, 

 iron oxide 0.1%. 



Gabriel has reported that the amount of fluorine in teeth is no 

 greater than in the bones, about 0.1%. 



Gr'assman reports that different teeth in the mouth of the same 

 individual have different compositions, and he considers the 

 frequent early decay of wisdom teeth to be due to a lower con- 

 tent of organic material and a higher content of lime than the 

 other teeth. 



Much work is needed to clear up the causes of dental caries. 

 Rose considered tooth decay to be connected with a deficient 

 supply of calcium salts. Recent work has brought out the ap- 

 parent connection between one of the vitamines, C, and the 

 teeth. Degenerative changes in the teeth have been reported as 

 the first effect of a shortage of C in the diet. 



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 



