ENAMEL 47 



oral epithelium, is the most constant indication of tooth 

 formation whether followed or not by calcification, and even 

 in man the epithelial cells are said to extend at the sides and 

 base of the dentine germ beyond the point at which enamel 

 ceases to be formed, as the epithelial sheath of Hertwig. 

 The author has shown, however, that there is every evidence 

 that this extension of epithelial cells is not an extension of 

 the layers of the enamel organ, but that it is derived from 

 other epithelial elements of the follicle. He has shown that, 

 in man as well as in Rodents, the enamel organ ceases at the 

 neck of the tooth where the enamel terminates. This ques- 

 tion will be further considered in describing the structure 

 and functions of the epithelial sheath of Hertwig (p. 320). 



In a tissue of such extreme hardness as enamel we should Chemical 

 naturally expect to find a great preponderance of inorganic tionof U 

 salts, and some authorities have even asserted that there enamel, 

 is no animal matter in the fully calcified enamel. Von 

 Bibra's (2) analysis of enamel is as follows : 



Calcium phosphate and fluoride . . 89*82 



Calcium carbonate i 4-37 



Magnesium phosphate ,. . . . 1-34 



Other salts . . . . . 0-88 



Cartilage . . . ' .' . . . 3-39 



Fat . ... . . . 0-20 



This analysis is seen to give : 



Organic substances . . . . . 3-59 

 Inorganic substances . . . . 96-41 



In the adult female Von Bibra estimates the amount of 

 animal matter as 5-97 per cent. 



The two principal lime salts present in enamel are seen 

 to be calcium phosphate and calcium carbonate, but in the 

 completed tissue the calcium phosphate largely predominates, 

 Von Bibra giving 89-82 of calcium phosphate and fluoride 

 to 4-37 of calcium carbonate (the fluoride only contributing 

 about 2 per cent.), magnesium phosphate being present in 

 the proportion of about 1-3 per cent. 



Hoppe-Seyler (9) considers that in human teeth the 

 phosphate and carbonate ot lime exist in combination 



