636 THE TEETH. 



First. Secondary dentine resembling primary dentine. 

 Second. Secondary dentine with a laminated structure. 

 Third. Secondary dentine in form analogous to Haversian systems. This 

 latter variety has been termed " osteo-dentine." 



Secondary dentine, with the essential structure of primary dentine, is 

 evidently the most frequent occurrence. It never has the regular arrange- 

 ment of the dentinal canaliculi as seen in primary dentine, but is marked 

 by a lighter color, owing to the larger amount of basis-substance and the 

 relatively small number of canaliculi, which at the same time deviate more or 

 less from the direction of the primary canaliculi. In cross-sections of such 

 secondary dentine especially in specimens stained with chloride of gold 

 we recognize in each canaliculus a central fiber, from which delicate conical 

 offshoots emanate toward the periphery of the canaliculus. The canaliculi, 

 which as a rule are the wider the nearer to the pulp- 

 cavity, are pierced on their periphery by light inter- 

 \.pjj ruptions, leading into a delicate, light reticulum 

 throughout the whole basis-substance. (See Fig. 

 274.) This secondary dentine sometimes remains in 

 an embryonal condition, exhibiting roundish fields of 

 basis-substance, such as are visible in the dentine of 

 a nine-months foetus. The medullary elements, being 

 transformed into basis-substance, represent irregular 

 globular bodies, between which the living matter pro- 

 duces the formations known as dentinal fibers. The 

 origin of these fibers will be fully understood only 

 after thorough investigation of the development of 

 dentine. This much is certain, that the regular fibers 

 FIG. 274. DENTINE O f secondary dentine are also beaded, and send lateral 

 OF AN AGED PER- offshoots toward the basis-substance, thus indicating 

 SON. CROSS -SEC- the p res ence of living matter in the latter. (See Fig. 

 TION. 275.) 



PD, primary dentine; Formations known as "interglobular spaces" are 

 ID, secondary dentine. not infrequently met with in normal dentine. They 

 Magnified 1000 diam- 



are also quite common in secondary dentine, especially 



on the boundary between primary and secondary den- 



tine. The tooth first described furnishes beautiful samples of such forma- 

 tions. Most of these are filled with bioplasson, some exhibiting nuclei. The 

 offshoots are evidently fibers of living matter. Some of these, toward the 

 primary dentine, are in direct communication with its fibers ; others run in 

 different directions toward neighboring kindred formations, with which they 

 inosculate ; others, again, after repeated bifurcation, lose themselves in the 

 basis-substance. Exceptionally there occur also bioplasson bodies without 

 any coarser offshoots. (See Fig. 273.) 



With higher amplification we see bioplasson bodies imbedded in lacunae of 

 the basis-substance, essentially identical with the so-called " interglobular 

 spaces," the tenants of which never could have been made out in sections 

 obtained from dry teeth. The plastids send larger beaded fibers in different 

 directions into the basis-substance, which are partly in communication with 

 fibers arising from neighboring bodies. (See Fig. 276.) 



The second variety of secondary dentine consists of the formation of a 

 lamellated basis-substance, which is traversed by irregular dentinal canaliculi. 



