XXX INTRODUCTION. 



the tooth-bone in the relation of a gland to its secretion ; that the 

 formative virtue of the pulp resided in its surface ; that the dentine 

 was deposited upon and by the formative or secretive surface of the 

 pulp in successive layers ; and that the pulp, exhausted as it were, 

 by its secretive activity, diminished in size as the formation of the 

 tooth proceeded ; except in certain species, in which the pulp was per- 

 sistent, and maintained an equable secretion of the dentine throughout 

 the life-time of the animal(l). 



This idea of the pulp's function, modified only by the phraseo- 

 logy required to express the later-acquired knowledge of the form 

 and condition of the newly-developed dentine in contact with the 

 pulp, has predominated in the minds of most subsequent writers on the 

 development of teeth. 



The successive steps to the establishment of the doctrine that 

 the cells of the ivory, under which form Dr. Schwann has described 

 the nascent dentine to make its first appearance, are actually part 

 of the pulp itself, pre-existing in that body before their calcification 

 and confluence, and continuing in organic connexion therewith after 

 their conversion into the tubular dentine, are few, well-marked, and 

 easily traced. The first advance was made by Purkinje and Rasch- 

 kow in submitting to careful microscopical observation the structure 

 of the dentinal pulp prior to the formation of the dentine, and 

 in similarly tracing the changes which it undergoes during that 

 process. 



(1) Cuvier, by whom this opinion of the formation of dentine is most clearly set forth, 

 premises the following acknowledgment : " Quant a la maniere dont les dents en general 

 naissent et croissent, nos observations nous paroissent confirmer la theorie de Hunter, plut6t 

 que toutes les autres, dans ce qui concerne la partie de la dent qu'on nomme substance 

 osseuse." — Ossem. Foss. 4to. 1812, p. 59. 



