TEETH. 



711 



wliieh commence at tlic 2)ulp cavity, and pass up to tlie 

 enamel. 



Czermak discovered that the curious appearances of 

 globular conglomerate formations in the substance of 

 dentine depend on its mode of calcification and the 

 presence of earthy material ; and he attributes the contour 

 lines to the same cause. Contour markings vary in in- 

 tensity and number ; they are most abundant in the root, 

 and most marked in the crown. Vertical sections exhibit 

 them the best; as hg. 342, ]^o. 1. In preparing a specimen, 

 lirst make the section accurately, 

 then decalcify it by submersion in 

 dilute muriatic acid ; then dry it 

 and mount in Canada balsam with 

 continued heat, so as to allow the 

 specimen to soak in the fluid resin 

 for some time before it cools. It is 

 the white opacity at the extremity 

 of the contour markings vi^hich 

 gives the appearance of rings on 

 the tooth-fang. 



"The tooth-substance appears," 

 says Czermark, " on its inner sur- 

 face, nob as a symmetrical whole, but consisting of balls 

 of various diameter, which are fused together into a 

 mass with one another in different degrees, and on which 

 the dentinal tubes in contact with the germ cavity are 

 terminated. By reflected light, haclc-ground illumination, 

 one perceives this stalactite-like condition of the inner 

 surface of the tooth-substance very distinctly, by means of 

 the varied illumination of the globular elevations, and by 

 the shadows which they cast. Here one has evidently to 

 do with a stage of development of the tooth-substance ; 

 for the older the tooth is, the less striking in general are 

 these conditions, and the more even is the surface of the 

 wall of the germ-cavity. In very old teeth considerable 

 nnevenness again makes its appearance ; these, however, 

 are not globular, but have a cicatrised, distorted appear- 

 ance. It is best to make the preparation from a tooth of 

 which the root is not perfectly completed. With such 

 preparations, one is readil}'^ convinced that the ground- 



Fig. 343. — Transvprse section of 

 Tooth of Prifttis, showing ori- 

 fices of medullary canals, with 

 systems of radiating fibres 

 (tithidi) analogous to the 

 Haversian canals in true 

 bone. 



