DENTINE 283 



contents would afford a very efficient means of distribution 

 of the calcifying substance within the matrix. It was 

 pointed out by Erwin Hohl (9), that in longitudinal section, 

 while the sheath of Neumann is very evident, with suitable 

 staining, in the calcified portion of the dentine, it is not to be 

 seen in the odontogenic zone, where the tubes appear to 

 have no definite walls. This observation is confirmed by the 

 author's silver- stained sections. Hohl considers that this fact 

 points to ' the dependence of the sheath of Neumann on 

 calcified dentine substance ' . 



Whether this sheath is concerned in the calcifying process 

 and serves the purpose of a dialysing membrane might be 

 considered, but if this lining sheath to the tubules really 

 exists or not is still considered by some a matter of con- 

 troversy ; its presence would not, however, appear to be 

 necessary to account for this mode of impregnation of the 

 matrix, for such dialysis could take place through the outer 

 limiting membrane of the dentinal fibril into the matrix 

 substance, and, as stated above, its permeation by the 

 minute subdivisions of the tubes would much facilitate the 

 process. 



It is difficult to explain the deposit of the lime salts at 

 a distance from the odontoblast cell itself, unless we consider 

 that the dentinal fibril which is an extension of the cell takes 

 an active part in the process, as suggested. 



The Calcification of Vasodentine. Vasodentine is de- 

 veloped around the walls of a central pulp cavity which is 

 traversed by large and abundant blood-vessels, these vessels 

 becoming incorporated in the dentine as calcification pro- 

 ceeds, and not receding deeper into the pulp as they do in 

 Mammalia. 



As C. S. Tomes says : * In the calcification of the formative 

 pulp into vasodentine, this recession of its vessels does not 

 take place ; the whole vascular network of the papilla 

 remains, and continues to carry blood circulating through it, 

 even after calcification has crept up to and around it.' In 

 a vasodentine pulp the connective tissue is very abundant, 

 and forms a definite layer of fibres around its circumference. 

 These fibres had originally been looked upon as odonto- 

 blasts ; they occupy the position of the odontoblast cells in 



