THE TEETH. 



649 



PD 



SD 



and built up by dentine. The canaliculi of this dentine are parallel, and 

 between them is a finely retieular basis-substance, arranged as in the primary 

 dentine of temporary teeth i. e., poorly supplied with lime-salts. The den- 

 tinal canaliculi are very wide ; the basis-substance between them, on the con- 

 trary, is narrow. The regular dentine toward the periphery of the pulp-stone 

 is bounded by a narrow zone, which exhibits the structure of secondary den- 

 tine. This again blends with a still 

 narrower one composed of an indis- 

 tinctly lamellated bone-tissue, with 

 scanty but large bone-corpuscles. 

 The bony layer is followed by the 

 bounding layer of the specimen, of 

 a granular appearance, containing 

 scanty, angular or spindle-shaped 

 bioplasson bodies and a few den- 

 tinal canaliculi. (See Fig. 285.) 



C. Wedl is of opinion that these 

 formations arise from an inversion of 

 the odontoblasts into the middle of 

 the pulp-tissue, believing that den- 

 tinal canaliculi can only be formed 

 by odontoblasts. My observations 

 demonstrate that the odontoblasts 

 are nothing but medullary corpus- 

 cles arranged in rows. In the pres- 

 ent stage of our knowledge we have 

 no reason to assume that the medul- 

 lary corpuscles of the periphery of 

 the pulp are specifically destined for 

 the formation of dentine. It is just 

 as admissible to assume that the 

 blood-vessels in the pulp furnish a 

 certain variety of pabulum to the 

 medullary corpuscles, and under the 

 influence of this material they will 

 be transformed into the tissue of 

 dentine. Should medullary corpus- 

 cles, in consequence of a slight irritation or an augmented afflux of nourish- 

 ing material, arise in the middle of the pulp, they may also produce dentine 

 or bone. The laws, however, which control the new formation of tissues 

 are as yet far from being understood. 



History. G. Prochaska * first described that, when by attrition the teeth on 

 their upper surfaces are worn, there is within the pulp-chamber just as much 

 new material produced as there is worn away on the outer surface. 



Rousseau t found " osteoids " and " bony growths " in the pulp-cavity, but 

 states thatBertin has known this before him. 



A. Nasmyth t says: "Much diversity of opinion has already existed 

 respecting the connection of the pulp with the ivory of the tooth, and as to 



* " Oper. Minor. Anat. Physiol. et Pathol. Arg." Pars, ii., Viennae, 1780. 

 t"Anat. Comp. du Syst. Dent. Chez PHomme et Chez les Princ: Animaux." Paris, 

 1827. 



t " Researches on the Development, Structure, and Diseases of the Teeth." 1849. 



FIG. 285. DENTINIFICATION OF THE 

 PULP. 



PZ>, layer of primary dentine; SD, layer of 

 secondary dentine ; O, layer of lamellated bone- 

 tissue ; G, granular layer toward the pulp- 

 tissue. Magnified 600 diameters. 



