ENAMEL 



71 



there must of necessity be interspaces between them. Pro- The inter- 

 fessor Walkhoff (20) considers that the cement substance of P r js matic 

 the enamel, described by Von Ebner, Leon Williams, and other 8 

 observers as the interprismatic substance, does not exist, and 

 is in reality the outer or cortical layer of the prisms, or, as 

 he calls them, iheZentralkorper. C. S. Tomes also says : ' no 

 thoroughly distinct interstitial substance exists in enamel.' 

 The evidences, however, afforded by the development of 

 enamel and the marked staining of a substance between the 



FIG. 29. The intercolumnar bridges (from a teased preparation of 

 Elephant enamel ). ( x 600. ) 



prisms in marsupials, point to the actual presence of such 

 a substance altogether independent of the prisms. Leon 

 Williams considers the interprismatic substance to be a sepa- 

 rate material, formed separately from the prisms, and the 

 author's own investigations on the enamel of marsupials 

 appear to confirm this view. 



Another confirmation of the separate formation and 

 distinct nature of the interprismatic substance is given in 

 a recently published paper by the late Dr. G. V. Black and 

 Dr. F. S. McKay ( 1 ), in which they describe an endemic patho- 

 logical condition of the teeth occurring in certain districts 

 of the Rocky Mountains. This condition they call mottled 



