82 OF DENTINAL "TUBES." 



of soft tissue have been witii drawn may be also demon- 

 strated. Calcitication takes place by the deposition 

 in the matrix of rounded globular masses of calcareous 

 matter, which increase in size and ultimately coalesce. 

 A narrow portion of the matrix extending outwards 

 from each mass of bioplasm still remains permeable, 

 and the process of calcification proceeds so much 

 more slowly in this portion than in the rest of the 

 matrix that the dentine produced refracts differently, 

 and is harder in texture. 



123. Of Dentinal " Tubes." — The difference in refrac- 

 tion above referred to and always noticed in thin 

 sections has led observers to regard this more slowly 

 formed layer of dentine as the " wall " of the sup- 

 posed "tube." But in the recent state this "tube" 

 is occupied by uncalcified matrix, which can be torn 

 away from the already calcified dentine. The calcifi- 

 cation of the formed material corresponding to the 

 "tube" gradually proceeds, so that the space or 

 " tube " occupied by soft matter becomes nari'ower as 

 the dentine advances in age, and at last in many 

 cases the outermost portion becomes completely calci- 

 fied, in which case there is no " tube " at all. The 

 " dentinal tube" of the dry prepared specimen results 

 from the desiccation of the uncalcified organic matter 

 of the recent structure. The greater " width " of the 

 tube near the pulp, and its gradual reduction in 

 diameter towards the surface of the dentine ; the 

 existence of soft solid matter in the "tubes," as was 

 first demonstrated by Tomes ; and the relation of the 

 oval masses of bioplasm on the sui'face of the pulp to 

 the dentine, are all accounted for in the explanation 

 of the development and formation of the dentine 

 above given. 



123. Dentinal " Tubes " not canals for conveying 

 fluid. — Is it reasonable therefore to suppose that the 

 dentinal tubes are really channels for the conveyance 

 of nutrient fluid from the surface of the vascular pulp 



