250 MICROSCOPIC ANATOMY OF THE TEETH 



shows the dentinal sheaths, but, as stated by Kolliker, the 

 fibrils cannot be seen. Hoppe (10) and others have also 

 demonstrated it in fossil teeth, where it is quite certain that 

 no protoplasmic material can be present. 



Romer considers that the dentinal fibril or process of 

 the odontoblast is tubular and contains a fluid or semifluid 

 substance, but his description of this hollow fibril as the 

 dentinal tubule is, we think, singularly unfortunate and leads 

 to much confusion. The nerve fibres which he describes as 

 entering the dentine he thus considers run within the tubular 

 dentinal fibril. For the history of these different views and 

 the full literature on the subject the reader may be referred to 

 Summary, the original paper (18). From this and other observations on 

 the structure of the tubes and fibril the following would 

 appear to be the best-established views of these structures. 

 The odontoblast cell is provided with a process, the dentinal 

 fibril, which enters the dentinal tube. This process is 

 a prolongation or extension of the protoplasm of the cell, 

 and carries with it into the dentine an extension of the 

 delicate cell membrane which invests the odontoblast cell. 

 This enclosing membrane stains, according to Hanazawa, with 

 hsematoxylin, but the fibril cannot, we think, be accurately 

 described as a tube, but simply as a protoplasmic process 

 with a slightly denser, stainable outer layer. The fibril 

 does not, judging from appearances, entirely fill the tube, 

 but there is a slight space around it along which fluids 

 can pass. 



The lining of the dentinal tube along which this fibril 

 passes would appear to be of a distinctly different consistence 

 to the rest of the matrix, and it colours with basic stains 

 and with silver nitrate. This lining, usually described as the 

 sheath of Neumann (and not considered to exist by Romer), 

 is shown by Hanazawa to be present, but he says it is not 

 unusually resistant to acids, thus differing from Neumann, 

 Tomes, and others. 



The substance which is isolated after the dentine matrix 

 has been destroyed by strong acids he considers to consist 

 of the dentinal fibrils themselves, which he says show more 

 resistance to acids than the walls of the tubes. He describes 

 the fibril as nearly filling the dentinal tube, only a very slight 



