292 



DIGESTIVE ORGANS. 



[sect. 137. 



According to Von Bibra, the chemical composition of dry dentine 

 is the following: — 



Molar Tooth of a Man . 

 Phosphate of Lime and some Fluoride of Calcium . 6672 



According to Tomes, fresh teeth, after the removal of the pulp, 

 lose £ to T \ of their weight when dried. The organic basis of the 

 teeth, which may be readily obtained by treating them with hydro- 

 chloric acid, is quite identical with that of the bones, and is readily 

 convertible into gelatine by boiling. This tooth-cartilage, as it is 

 termed, completely retains the form of the dentine, and, except 

 that the tubes are with difficulty visible, even its internal structure. 

 If it be macerated in acids or alkalies until it is quite soft, the 

 matrix is found in the act of disintegration, but the dentinal tubes, 

 with their walls, are still preserved, and may be isolated in large 

 quantities (see my Micr. Anat. ii. 2, p. 61, fig. 189). When still 

 longer macerated, everything is dissolved. The dentinal tubes 

 may be also isolated after long continued boiling of the tooth- 

 cartilage. When a tooth is exposed to a red heat, the inorganic 

 parts remain behind, and retain the form of the tooth, just as 

 when it is treated with caustic alkalies. The dentine, accordingly, 

 like the bones, with which it agrees so very much in its chemical 

 composition, is made up of an intimate mixture of organic and 

 inorganic parts. 



The apparent walls of the dentinal tubes, which are usually seen upon the 

 transverse sections (fig. 120), are not the true walls of the canals, but rings, 

 the appearance of which arises from this, that a certain length of the canals 

 is always seen with the microscope in the thickness of the section, never 

 sufficiently fine to obviate this effect, and the short tubular segments being 

 curved in direction, a greater apparent thickness is thus given to the walls 

 than they really possess. If, upon a transverse section, the openings of the 

 canals be brought accurately into focus, we perceive, instead of a dark ring, 

 only a yellowish, very narrow edge, and it is this that I regard as being the 

 true wall. 



The dentine not unfrequently presents indications of a lamellation, which, 

 in longitudinal sections, appears in the form of arched lines (fig. 1 22), coursing 



