CEMENT 299 



of the cell substance into bone. This view was upheld by 

 Gegenbaur and Kolliker, while Waldeyer (9) and others 

 maintain that there is a ' direct conversion of the protoplasm 

 of some of the osteoblasts into bony tissue '. Schafer, in 

 supporting the secretion theory, points out that there is no 

 indication of cell areas in the formed tissue, and no half- 

 calcified osteoblasts are to be seen. 



As is seen in fig. 191, which shows the penetrating fibres 

 in the cement in a Weil preparation from a tooth freshly 



FIG. 194. Forming cement showing that it is deposited in flakes. The 

 faintly stained cells between the flakes are the osteoblasts. ( x 450.) 



fixed in sublimate, the Sharpey's fibres appear as channels 

 in the substance of the tissue communicating with the 

 exterior and in close contact on the inner side with the 

 granular layer of the dentine. If these run, as they appear 

 to do, in actual channels in the cement, they may serve 

 as a means of communication between the fibrils of the 

 dentine and the periodontal membrane, and in the absence 

 of lacunae with their canaliculi, may serve to keep up this 

 communication. In caries in the cement the micro- 

 organisms penetrate the tissue along the lines of these fibres 

 exactly as they do the tubes of the dentine. 



Absorption. Absorption occurs in the temporary teeth 

 as a normal physiological process, and is the agency by which 



