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J. A. GRAY AND M. D. FRANCIS 



19 



Figs. 14 and 15. A section of an incipient carious lesion produced by a 

 96-hour exposure at 4°C to a medium consisting of 0.04 m lactic acid, 0.03 m 

 CaCl2, and 0.01 m NaHoP04 plus 6 per cent hydroxyethyl cellulose adjusted to 

 pH 3.5. The right side of the enamel surface was protected from the medium 

 by a varnish coating. 



Fig. 14. The light micrograph, taken with ordinary light, shows a lesion 

 about 75 microns in depth and containing three bands. ( X 200. ) 



Fig. 15. The microradiograph shows both the very great loss of subsurface 

 enamel and the very considerable relatively sound outer layer. The surface 

 of the enamel was unchanged as determined microscopically with top illu- 

 mination. The increase in decalcification as compared with Figs. 10 and 11 



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