TOOTH STRUCTURE. 531 



salts being washed from the bones in osteomalacia by means of lactic 

 acid. They have given special prominence to the fact that the lime- 

 salts held in solution by the lactic acid must be deposited on neutraliza- 

 tion of the acid by the alkaline blood. This objection is not very impor- 

 tant, as the alkaline blood-serum has the property to a high degree of 

 holding earthy phosphates in solution, which fact can be easily proven. 

 The investigations of LEVY 1 contradict the claim as to the solution of 

 the lime-salts by lactic acid in osteomalacia. He found that the normal 

 relation 6PO 4 :10Ca is retained in all parts of the bones in osteomalacia, 

 which would not be the case if the bone-earths were dissolved by an 

 acid. The decrease in phosphate occurs in the same quantitative 

 relation as the carbonate, and according to LEVY, in osteomalacia the 

 exhaustion of the bone takes place by a decalcification in which one 

 molecule of phosphate-carbonate after the other is removed. 



In rachitis the quantity of organic matter has been found to vary between 664 

 and 811 p. m. The quantity of inorganic substance was 189-336 p. m. These 

 figures refer to the dried substance. According to BRUBACHER, rachitic bones 

 are richer in water than the bones of healthy children, and poorer in mineral 

 bodies, especially calcium phosphate. In opposition to rachitis, osteomalacia 

 is often characterized by the considerable amount of fat in the bones, 230-290 

 p. m., but as a rule the composition varies so much that the analyses are of little 

 value. In a case of osteomalacia, CHABRIE 2 found a larger quantity of magne- 

 sium than calcium in a bone. The ash contained 417 p. m. phosphoric acid, 222 

 p. m. lime, 269 p. m. magnesia, and 86 p. m. carbon dioxide. Other investigators 

 have on the contrary found considerably more calcium than magnesium. 



The tooth-structure is closely related, from a chemical standpoint, 

 to the bony structure. 



Of the three chief constituents of the teeth dentin, enamel, and 

 cement the cement is to be considered as true bony structure, and as 

 such has already been discussed to some extent. Dentin has the same 

 composition as the bony structure, but contains somewhat less water. 

 The organic substance yields gelatin on boiling; but the dental tubes 

 are not dissolved, therefore they cannot consist of collagen. In dentin 

 260-280 p. m. organic substance has been found. Enamel is an epithe- 

 lium formation containing a large proportion of lime-salts. Correspond- 

 ing to its character and origin, the organic substance of the enamel 

 does not yield any gelatin. Completely developed enamel contains 

 the least water, the greatest quantity of mineral substances, and is the 

 hardest of all the tissues of the body. In full-grown animals it contains 

 hardly any water, and the quantity of organic substance amounts to only 

 20-40-68 p. m. The relative amounts of calcium and phosphoric acid 

 are shown by the analyses of HOPPE-SEYLER to be about the same as 



1 Zeitschr. f . physiol. Chem., 19. 



2 Chabrie, Les phenomenes chim. de 1'ossification, Paris, 1895, 65. 



