DENTINE 249 



relations of the dentinal fibril to the tube of the dentine. 

 Romer considers that there is no definite wall to the dentinal 

 tube, which is merely an interval or channel in the matrix : 

 he thus does not acknowledge the existence of the sheath 

 of Neumann as a definite structure. He considers the so- 

 called Neumann's sheath to be a part of the soft fibril, 

 and that in the preparations in which it is claimed that the 

 sheath is stained, what is really stained is the outer surface 

 of the soft dentinal fibril. He shows a figure in the illustra- 

 tions to his paper on the subject in which, in transverse 

 section, the fibril has fallen out, and there is a perforation 

 in the dentine with no wall to it. Judging by the illustration 

 it would seem that in this instance the fibril only is stained, 

 and the sheath not, as the author has several preparations 

 which show an outer ring enclosing another dark-stained 

 ring which is the border of the dentinal fibril. 



In these preparations stained by a modification of the 

 silver nitrate method of Ramon y Cajal, the sheath of Neu- 

 mann is stained a deep black, and the dark-stained fibril 

 is seen lying within the ring, an appearance which cannot 

 be explained on the assumption that the supposed sheath 

 is the outer border of the stained fibril (fig. 152). In this 

 photograph it is to be seen that at the thinned- off margin 

 of the section the segments of circles are visible, surrounded 

 by a thin black line, and at the margin of these segments 

 this thin line is seen to project from the dentine, indicating 

 that it is a firm substance not connected with the fibril and 

 firmer than the surrounding matrix substance. 



A very elaborate examination into the minute structure 

 of dentine has lately been undertaken by Professor Hana- 

 zawa of Tokyo (11). He made use of very many different 

 reagents and methods of staining, and concludes that the 

 wall of the dental tubule has no special resistance to acids 

 or alkalis, and cannot be isolated, and it is unreasonable to 

 call it a sheath, and that the fibrillar substance isolated by 

 mechanical and chemical methods is the dentinal fibril and 

 not the sheath of Neumann. A strong argument, however, 

 for the view that this residue consists of Neumann's sheath 

 is found in the fact mentioned by Tomes, that a tooth 

 section boiled in a caustic alkali or allowed to putrefy still 



