

CHEMICAL PHYSIOLOGY. 47 



carbonate, 87' 7 of calcium phosphate (Ca 3 Po0 6 ), 1/7 of 

 magnesium phosphate (Mg 3 P 2 6 ), and 3 per cent, of 

 calcium fluoride (CaF 2 ). The nutrition of the bones 

 proceeds from their surface towards their cavities. 

 Certain dyes, given with the food, penetrate into the 

 bones and stain them. The idea formerly combined 

 with this experiment, namely, that the bone was 

 rapidly renewed from without and absorbed ^in the 

 marrow cavity, is probably quite untenable. In 

 several important diseases the bones are greatly 

 affected, and become either brittle, or soft and bend. 

 Such diseases are rhachitis, or rickets, common in 

 children, the osteomalacia of pregnant women, and Osteomalacia - 

 that particular form which attacks aged persons. In 

 these diseases the bone-earth falls to about 30 per 

 cent, of the dry bones, while the osseine rises to 60 

 and 80 per cent. The osseine at the same time 

 changes its chemical character, by a curious tissue 

 transformation, starting from the marrow cavities, and 

 now no longer yields glutine. It seems that the agent 

 by means of which in this no doubt complicated 

 process the earths are removed is lactic acid, which Jj^ acid in 

 under these circumstances, and not in health, is found 

 in and about the bones. These diseases urgently call 

 for chemical investigation. 



The teeth are bones, of which a part, the root, is con- Teeth. 

 structed like ordinary bone ; while the top or crown is 

 formed upon a particular plan, round many minute 

 tubes ; this latter tissue is termed dentine. The outer Dentine. 

 hard covering, the cement, is an epithelial formation, cement, 

 containing only 4 per cent, of organic matter, 92 per 



