TISSUES OF THE BODY. 



275 



158. 



This substance enamel, now under consideration, is the hardest and 

 densest in the body, and admirably suited for the protection of the sub- 

 jacent dentine. In this respect, however, the prisms are excelled by the 

 enamel cuticle. 



As far as we know of the chemical constitution of this tissue, it is the 

 poorest in water of any in the system, and most rich at the same time in 

 inorganic constituents. For every 2, 4, or 6 per cent, of organic matter 

 which retains the form of the prisms after treatment with acids, but which 

 yields no glutin on boiling (Hoppe), we find 81-90 per cent, of phosphate, 

 4-9 of carbonate, and more than 3 per cent, of fluoride of calcium 

 (according to Berzelius}} also 1*5-25 of phosphate of magnesium. We 

 shall take as examples the two following analyses of Bibra, of which 

 the first refers to the enamel from the molar tooth of an adult man, and 

 t he latter to that from a woman of twenty-five years of age : 



1. 2. 



Organic substratum, .... 3'39 (?) 5.97 



Fat, 0-20 ' traces 



Phosphate and fluoride of calcium, . . 89 '82 81'63 



Carbonate of calcium, . . . . 4' 3 7 8-88 



Phosphate of magnesium. . . . 1'34 2 -55 



Other salts, ..'.... 0'88 0'97 



Partially developed enamel is naturally far richer in organic constituents. 

 The substratum of organic matter found in the enamel cuticle is remark- 



Fig. 264. 



able for its power of resisting acids and alkalies. It yields, moreover, no 

 glutin (Koelliker). 



The development of enamel takes place, as has long been known, from 

 the cells clothing the concave surface of the enamel organ (fig. 258, c), 

 and in such a way that each future prism corresponds to a cell. The 

 process is, however, still a matter of controversy, although everything 

 seems to point to the conclusion that a calcification of the bodies of the 

 cells takes place. 



As we are already aware, the latter at first appear in the form of cylin- 

 drical structures, with vesicular nuclei and very delicately granular con- 

 tents, and of about the same breadth as the prisms. Later on, as the 



