DEVELOPMENT OF THE ENAMEL 167 



and the enamel matrix, it can easily be understood that the 

 fibril would continue to penetrate this slightly resisting 

 substance until eventually closed round by calcification. 



The chemical composition of adult enamel presents a 

 problem which it is somewhat difficult to elucidate in view 

 of these observations on calcification. 



It is seen that the calcific deposit in the interprismatic 

 substance takes place in the form of large calcospherites, 

 and that, despite opinions to the contrary, the globular form 



FIG. 97. Developing tooth of Macropus. e. Forming enamel ; c. calco- 

 spherites ; d. calcified dentine ; o. odontogenic zone (cut without 

 decalcification). ( x 500. ) 



is the form in which lime salts are deposited in the hard 

 tissues of the teeth. 



In the artificial experiments where these large calco- 

 spherites are deposited in albumin and other media, they 

 consist of carbonate of lime, and although it was shown by 

 Professor Harting that when a little phosphate of lime was 

 present with the carbonate the largest and most perfect 

 spherites were formed, if the phosphates were at all in excess 

 of the carbonates, spherites were not formed but the deposit 

 was crystalline. 



The analyses of adult enamel show a very great prepon- 

 derance of phosphates over carbonates roughly 89 per cent, 

 of phosphates to 4 per cent, of carbonates. In view of this 



