ENAMEL 59 



of the tissue elements and in their calcification, and he found 

 that the teeth of the anthropoid apes showed defects in the 

 structure of the enamel exactly similar to those in man. 



Other explanations have been given of the cause of the Striation 

 cross-striation of the enamel prisms from that given above. 

 Von Ebner (66) holds that it is the result of the action of 

 acids , but these striae can be seen in prisms which have not been 

 treated with acids. Fragments scraped from the forming 

 enamel of a dry human tooth still in its crypt and teased 

 out in glycerine on a slide show these markings very distinctly. 

 That this cannot be due to any acid that may be present 

 in the glycerine is shown by the fact that they are quite 

 as evident when examined in alkaline Farrant solution. 



Hertz described the striae as due to the intermittent 

 calcification of the enamel rods. The generally accepted 

 view is that they are due to varicosities in the prisms, but 

 this seems to be describing the condition without any 

 reference to its cause. There seems little doubt that the 

 appearance is due to varicosities, but the cause of these is 

 the mode of deposition of the lime salts in the prisms of the 

 enamel. These are made up, as Harting (7) originally said, 

 of little piles of calcospherites, and are due. as Leon Williams 

 has pointed out, to the succession of these regularly deposited 

 calcified bodies within the cytoplasmic strings which form 

 the foundation of the enamel rods, as will be more fully 

 explained when describing the calcification of enamel. 

 Fig. 22, from a preparation of the author's of developing 

 marsupial enamel teased out in glycerine, shows in several 

 places the beaded prisms made up of a regular deposit of 

 small calcified bodies and helps to confirm this view of the 

 nature of these striae. 



The suggested analogy with the varicosities of voluntary 

 muscle fibres can scarcely merit serious attention, as the 

 varicosities in enamel are due to its mode of calcification 

 and are dependent upon enamel being a calcified tissue. 

 The opinion of Hannover and Hertz that they are 4ue to 

 the intermittent calcification of the enamel rods was there- 

 fore very close to the real explanation, although these 

 authors did not describe the actual mode of deposition of 

 these uniform calcified elements of the prism. 



