What relation then does the ivory bear to the cells? I must at once avow that I cannot give a positive reply to this question, and that I only communicate the following imperfect investigation for the sake of presenting a connected view of my subject. The formation of the dental substance is described by Purkinje and Raschkow as follows: “ Primordio substantia dentalis e fibris multifariam curvatis convexis late- ribus sese contingentibus ibique inter se concrescentibus com- posita apparet. . . . . In ipso apice iste fibre equaliter quam- cunque regionem versus se diffundunt, attamen parietes laterales versus directiolongitudinalis preevalet, dum fibree sinuosis flexibus eequalique modo se invicem contingentes ibique ubi concave apparent lacunas inter se relinquentes, ab apice coronali radicem versus ubicunque procedunt. Non nisi extremi earum fines tune molles sunt cetere autem partes brevissimo tempore indurescunt. . . . . Substantiae dentalis formationis secundum crassitudinem processus pari modo ac primo ejus ortu cogi- tandus est. Postquam.... . fibrarum dentalium stratum depositum est, idem processus continuo ab externa regione internam versus progreditur, germinis dentalis parenchymate materiam suppeditante. . ... Convex fibrarum dentalium flexure, que juxta latitudinis dimensionem crescunt, dum ab externa regione internam versus procedunt, sibi invicem apposite continuos canaliculos effingunt, qui ad substantiz dentalis peripheriam exorsi multis parvis anfractibus ad pulpam dentalem cavumque ipsius tendunt, ibique aperti finiuntur, novis 1bi, quamdiu substantiz dentalis formatio durat, fibris dentalibus aggregandis inservientes.” (Raschkow, Meletemata circa Mammalium dentium evolutionem. Vratislav. 1835, p. 6.)
I must admit that I do not clearly understand some of this description, but if I rightly comprehend it, the dental substance originates from fibres which are formed in strata around the pulp (the latter supplying the material for the purpose); that these fibres then coalesce, leaving, however, spaces between them which are the dental tubes. Since, according to Müller, the tubes are furnished with special walls, we can no longer regard them as mere spaces between the fibres. His observation, however, does not affect the explanation of the formation of the firm substance.
