248 MICROSCOPIC ANATOMY OF THE TEETH 



contour may not indicate a distinct wall to the tube. 1 

 The existence of such wall to the tube is denied by some 

 observers, and considerable controversy has arisen as to 

 the exact structure, and the relations of the dentinal tube, 

 matrix, and dentinal fibril within the tube. Most authorities, 

 however, consider there is a distinct lining substance to the 

 tube the sheath of Neumann (16). This is considered to 

 be of the nature of a tissue on the borderland of calcification ; 

 it is indestructible by strong acids and remains, after thorough 



FIG. 152. Human premolar. Transverse section (silver pyridin). 

 Showing stained sheath of Neumann. t (x800.) 



destruction of the collagen basis, as a confused mass of 

 fibres consisting of elastin (C. S. Tomes). 



The den- In living dentine the tubes are occupied by a soft fibril, 

 ajjjj * the dentinal fibril, which is a prolongation of the substance 

 sheath of o f the odontoblast cell in the pulp. The dentinal fibril was 

 * first described by Sir John Tomes (21). It is accompanied 

 within the tube by one or more neurofibrils prolonged from 

 the nerve-end cells in the pulp, which course with it through- 

 out the dentine. The neurofibrils are not visible in dentine 

 when stained by ordinary methods, but are only revealed by 

 the employment of special methods of staining. As stated 

 above, various opinions have been held as to the exact 



1 In caries of the dentine an extraordinary amount of thickening o- 

 the tube wall is often seen. 



