THE DENTAL TISSUES. 



demonstrated in fossil teeth, in teeth boiled in caustic 

 alkalis, or in teeth which have been allowed to putrefy. 



Although Kolliker was, I believe, the first to describe and 

 figure these isolated tubes, they are generally known as the 

 " dentihal sheaths of Neumann," the latter writer having 

 more fully investigated and described them. The precise 

 chemical nature of these sheaths will be more conveniently 

 considered under the head of calcification : similarly inde- 

 structible tissues are, however, to be met with surrounding 

 the Haversian canals and the lacunae of bone. It is the 

 opinion of Neumann, as it was also of Henle, that the 

 dentinal sheaths are calcified; but the proof of this is. 

 very difficult, as they cannot be demonstrated, or I should 

 rather say, isolated, to any extent in dentine, unless -it has, 

 been decalcified. Their existence has been recently denied 

 in toto by Magitot. 



Transverse sections of dentine present fallacious appear- 

 ances, owing to the thickness of the section giving to the 

 tube a double contour which may be easily mistaken for a 



FIG. 27 ( J ). 



special wall. Immediately round the opening of the canal, 

 or " lumen," as it is called, there is however generally a 

 thin yellowish border, which is the sheath of Neumann. 

 In the earlier stages of caries, before the dentine is much 

 softened, the walls of the canals become strikingly appa- 



( ] ) Transverse section of dentine. The appearance of a double contour 

 is so much exaggerated as to make the figure almost diagrammatic. 



