56 MICROSCOPIC ANATOMY OF THE TEETH 



segment of the enamel column which strongly suggests that 

 the enamel is built up in this manner. 



Summary Perfect enamel then consists, according to this author, 

 Wiufams's ^ ^ e prisms, for which he has substituted the term ' rods ', 

 views. made up of vertical rows of calcified disks in close apposition 

 but sufficiently separated to show the cross-striation which 

 marks their line of junction, and of a densely calcified cement- 

 ing or interprismatic substance. Delicate plasmic strings 

 are to be seen running vertically within the substance of 



FIG. 18. Enamel (longitudinal ) showing granular structure 

 of prisms. ( x 800. ) 



the calcified rod, and calcified connecting bridges pass 

 horizontally between them (fig. 14). 



The vertical rows of calcified disks forming the rods 

 are built up of minute coalesced granules. 



There is little doubt that this is a true description of the 

 structure of enamel of perfect quality, but Leon Williams's 

 statement that enamel is an entirely inorganic tissue requires 

 some modification, for the reason that enamel in human 

 teeth is seldom, if ever, a perfect tissue. Imperfections in 

 structure, especially at the dentine margin, and minute 

 channels from the dentine are so frequent as scarcely to 

 be looked upon as abnormalities. 



