THE TEETH. 



667 



filled with the same granular mass that is present in the fissures, consisting 

 evidently of debris of the former tissue, together, perhaps, with micrococci, 

 and very often fine, thread-like leptothrix. The more rapidly the destruction 

 of the dentine has advanced, the more irregular islands of dentine are left on 

 the surface. 



The outermost portion of the decayed part is, as a rule, brittle, and crum- 

 bles away in chromic acid specimens. Where it is left it shows a crowd of 

 leptothrix and micrococci, without any distinctly recognizable remnants of the 

 former tissue. On the boundary of the carious portion we, as mentioned 

 above, meet with a yellow discoloration of the dentine, evidently produced by 

 a chemical agent, which first dissolves out the lime-salts from the dentine, 

 and in turn liquefies the glue-yielding basis-substance. In live teeth the yel- 



FIG. 293. CARIES OF DENTINE. 



F, unchanged deutinal fiber: P, enlarged dentinal canaliculi, filled with bioplasson ; Jf^ 

 medullary corpuscles in considerably widened deutinal spaces ; G, complete transformation 

 of dentine into medullary corpuscles. Magnified 1000 diameters. 



low discoloration usually takes place in the shape of longitudinal strings of 

 different diameters, running mainly parallel with the longitudinal direction of 

 the dentinal canaliculi. Nay, we often see single yellow strings running from 

 the bottom of a carious cavity in the enamel through the whole depth of the 

 dentine to the pulp-chambers. While the unchanged dentine readily takes up 

 the carmine, the strings, the deep yellow color of which is undoubtedly due to 

 the action of the chromic acid, remain unstained. (See Fig. 292.) 



