XXIV INTRODUCTION. 



into apparently fine prismatic fibres ; if these fibres be separately 

 treated with dilute muriatic acid and the residue examined, with a 

 moderate magnifying 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 mould in which it was deposited. 



Professor Retzius, who obtained a small portion of organic or 

 animal substance from the enamel-fibres of an incompletely-formed 

 tooth of a horse, conjectured that it w^as a deposition of that fluid 

 which originally surrounds the loose enamel-fibres, and that, " in 

 proportion as these fibres are pressed tighter together, and additional 

 fibres are wedged between them, the organic deposition is forced 

 away." 



It is certain that the small proportion of animal matter which can 

 be obtained from the enamel of a tooth, that has been completely 

 formed and in use, does not yield any indication of its primitive or- 

 ganic form ; this may, however, be ascertained, if the enamel be 

 examined under the conditions above described. The tubular struc- 

 ture of the membranous constituent of recently formed enamel has 

 been observed by Dr. Schwann(l) in the teeth of the hog : and he 

 has shown that the fine membrane of the enamel-prism is not a mere 

 deposition from the fluid in which the new-formed prisms are bathed, 

 but an organized part specially formed and arranged in the enamel 

 pulp in order to ensure the right disposition and direction of the cal- 

 careous salts of the enamel. 



Retzius accurately describes the enamel-fibres of the horse as 

 presenting the form of angular needles, about gjooth of an inch in 

 diameter, which are traversed by minute and close-set transverse 



(1) Loc. cit. p. 118. 



