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A. I. DARLING 



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Fig 8. Ground section of tarly caries of human dental enamel mounted in 

 quinoline and seen by polarized light in the 45° position, (x 750.) The illustra- 

 tion shows normal enamel at the lower border and passes through translucent 

 zone and dark zone to the body of the lesion at the upper border. 



it is not yet possible to say definitely what material is lost to produce 

 the spaces in the translucent zone. 



The explanations offered on the quality of the attack are to some 

 extent modified by opinions on the precise structures involved and 

 their nature. 



Most workers now agree that there is a differential decalcification 

 of certain structures. Most seem to accept that the pattern of attack, 

 after the surface is penetrated, begins in the so-called interprismatic 

 region, then involves the cross striations or something very like them, 

 after which the prism becomes more completely involved, leaving 

 rings of unaffected enamel which correspond in size to prisms. The 

 precise location of these structures, however, is difficult to determine. 

 All seem to agree that the surface zone, rings of enamel correspond- 



