CHAP. VII.] THE CONNECTIVE TISSUES. 291 



is of opinion that in dentine, as in bone and enamel, the chief min- 

 eral ingredient is a definite compound (Ca 10 CO s , 6(PO 4 )) of calcium 

 phosphate and carbonate, constituted like apatite (Ca 10 Fl 2 , 6(POJ). 



Recalculating the results of an analysis of dentine of the ox made 

 by Aeby 1 , Hoppe-Seyler states its composition as follows : 

 Ca 10 C0 3 , 6PO. in 100 parts 72'06 



MgHP0 4 075 



Organic matter 2770 



100-51 



Numerous analyses of dentine by various chemists will be given 

 in the table exhibiting the general results of quantitative analyses of 

 tooth. 



Enamel, 



This tissue, the hardest in the body, as well as the richest in 

 mineral constituents, covers the crown or exposed surface of the tooth. 



In its adult condition enamel is composed of polygonal (usually 

 hexagonal) prismatic columns which rest upon the dentine and 

 radiate out from it. 



As has been already said, enamel is epiblastic in its origin, being 

 developed through the agency of the columnar epithelial cells of the 

 enamel organ, a structure produced by the proliferation and growing 

 downwards of the deeper epithelial cells of the oral mucous membrane. 



When enamel is digested in acids, only a small quantity (2 6 per 

 cent.) of organic matter is left, which does not yield gelatin on boil- 

 ing. Enamel is thus seen, on chemical as well as on developmental 

 grounds, to differ from the connective tissues. 



The mineral matters of enamel are essentially the same as those 

 of bone and dentine, and, according to Hoppe-Seyler, there are good 

 grounds to believe that they consist mainly of the same compound of 

 calcium phosphate and carbonate. Adult enamel contains a small 

 quantity of a fluoride, but Hoppe-Seyler failed to detect fluorine in 

 the growing enamel of the pig. It might be surmised that the 

 enamel consists of a mixture of apatite and bone earth, but there are 

 good reasons for believing that this is not the case. 



The following formulae exhibit the relations between apatite and 

 the peculiar salt which Hoppe-Seyler believes to be the characteris- 

 tic mineral ingredient of bone, dentine and enamel. 



Crystallized apatite .... Ca 10 Fl 2 , 6(PO 4 ) 

 (another variety) Ga 10 Cl 2 , 6(P0 4 ) 

 The bone earth salt . . . Ca 10 CO 3 , 6(PO 4 ) 



In the annexed tables are given, firstly the results obtained by 

 Hoppe-Seyler from his analyses of enamel, and secondly the probable 

 amounts of the mineral compounds which he assumes to have been 

 present, 



1 Aeby, Centrattlatt f. d. med. Wissenschaft. 1873. No. 7. 



192 



