THE GERM THEORY OF CARIES. 157 



by acids, then the fungus may penetrate the portions thus 

 softened and continue the destruction. Again, they say, " It 

 see~ras that the fungi are not able to penetrate an enamel of 

 normal consistency. The dentine itself, in its normal condi- 

 tion of density, offers great difficulties to their entrance, and 

 we are not yet sure that the leptothrix could triumph over 

 this resistance." Again, " We cannot decide at present if 

 the leptothrix is able to penetrate sound dentine, when from 



nny circumstance it happens to be denuded 



But, if the enamel or dentine are become less resistant at 

 any point, through the action of acids, or if, at the surface of 

 the dentine, a loss of substance has occurred, then the elements 

 of the fungus can pass into the interior of the dental tissues, 

 and produce by their extension, especially in the dentine, 

 effects of softening and destruction much more rapid than 



the action of acids alone is able to accomplish 



The participation of the fungus is constant in the progress 

 of caries which has reached this stage. As soon as a loss 

 of substance can be shown, there is found the presence of 

 the fungus, so that the question whether or no the acids 

 alone could produce ravages more considerable is without 

 importance." 



The modus operandi by which leptothrix may produce 

 softening of the dentine is left without explanation. We can 

 conceive, however, that they may do something to assist the 

 softening process by the outpouring of a digestive fluid. If, 

 however, this fungus gave a fluid that would digest a tooth, 

 we would think that sound teeth would be very scarce, for it 

 grows abundantly in every mouth. 



Since the time of Lieber and Rottenstein's work we remem- 

 ber of no other of much importance having appeared on this 

 subject. The discussion has continued, however, in the jour- 

 nals. We cannot now undertake to review this literature, 



