THE ENAMEL',.; VARIEGATED BEAUTIES. XIX 



and branches being reA'ersed, agreeably with the con- 

 trary course of their respective developments. The 

 proportion of animal matter is also greater in the 

 enamel of the teeth of fishes than in the higher verte- 

 brata, and the proportion of the calcareous salts incor- 

 porated with the animal constituent of the walls of 

 the tubes is greater as compared with the subcrystal- 

 line part deposited in the tubular cavities. 



"The enamel may be distinguished, independently 

 of its microscopic and structural characters, by its 

 glistening, subtransparent substance, which is wdiite 

 or bluish-white by reflected light, but of a gray-brown 

 color when viewed, under the microscope, by trans- 

 mitted light. * ^ * The enamel of the molar 

 tooth of a calf, which has just begun to appear above 

 the gum, and which can readily be detached from the 

 dentine, especially near the beginning of the roots, is 

 resolvable into apparently fine prismatic fibers. If 

 these fibers be separately treated with dilute muriatic 

 acid, and the residue examined with a moderate mao-- 

 nifying power, in distilled water, or, better, in dilute 

 alcohol, portions of more or less perfect membranous 

 sheaths or tubes will be discerned, which inclosed the 

 earthy matter of the minute prism, and served as the 

 mold in which it was deposited. 



"Prof. Eetzius, who obtained a small portion of 

 organic or animal substance from the enamel-fibers of 

 an incompletely-formed tooth of a horse, conjectured 

 that it was a deposition of that fluid whicli originally 

 surrounds the loose enamel-fibers, and that *in pro- 

 portion as these fibers are pressed tighter together, and 

 additional fibers are wedged between them, the organic 

 deposition is forced away.' 



"Retzius accuratelv describes the enamel-fibers of 



