DEFINITIOiN" OF DENTAL TISSUES. 231 



" Dentine" consists of an organized animal basis dis- 

 posed in the form of extremely minute tabes and cells, 

 and of earthy particles ; these particles have a twofold 

 arrangement, being either blended with the animal mat- 

 ter of the interspaces and parietes of the tubes and cells, 

 or contained in a minutely granular state in their cavities. 

 The density of the dentine arises principally from the 

 proportion of earth in the first of these states of combina- 

 tion. The tubes and cells contain, besides the granular 

 earth, a colorless fluid, probably transuded " plasma," or 

 " liquor sanguinis," and thus relate not only to the me- 

 chanical conditions of the tooth, but to the vitality and 

 nutrition of the dentine. 



In hard or true dentine, the tubes called "dentinal 

 tubes" diverge from the hollow of the tooth, called "pulp- 

 cavity," and proceed with a slightly wavy course at right 

 angles, or nearly so, to the outer surface. The hard sub- 

 stance of the tooth is thus arranged in hollow columns, 

 perpendicular to the plane of pressure, and a certain 

 elasticity results from their curves : they are upright 

 w^here the grinding surface of the crown receives the 

 appulse of the opposing tooth, and are horizontal where 

 they have to resist the pressure of contiguous teeth. In 

 Fig. 54, a highly magnified view is given of a small por- 

 tion of human dentine, showing the tubuli, in the inter- 

 tubular substance, with the traces of the primitive cellu- 

 lar constitution of that substance. For the mode in 

 which the nucleated cells of the primary basis of the 

 tooth, called " tooth-pulp," are converted into dentine, 

 reference may be made to the author's " Odontography" 

 (Introd., plates 1 and 2). The tubuli, besides fulfilling 

 the mechanical ends above stated, receive the plasma 

 transuded from the remains of the vascular pulp, which 



