168 THE GERM THEORY OF DISEASE. 



mally sensitive) until he can see the root of the tooth below 

 plainly, it will be easy to demonstrate that there has been a 

 decided loss of substance. Trial with an instrument will 

 develop the fact that the surface within this groove is ex- 

 ceedingly sensitive; the dentine is exposed. 



Now, if the case is left to itself, this sensitiveness will 

 continue for some weeks, or even months, and then abate ; 

 and it will be found that the case has taken on the usual 

 characters of decay. It may cease to progress and assume 

 a dark color, or it may progress rapidly, and remain of a 

 more or less ashy cast. 



It has been our opinion that this class of decays, if that 

 term can be applied at this stage, is brought about in pre- 

 cisely the same way that the root of a permanent tooth is 

 partially absorbed on account of a chronic irritation of its 

 peridental membrane. In other words, a soluble ferment has 

 been called out by the irritation that has dissolved out a part 

 of the tissue at that point. Or, if you prefer to have it put 

 in that way, a true absorption has taken place which forms 

 the nidus for the future decay. 



Another class of decays are very common, which I have 

 studied very closely, and which seem to be of the same 

 character in their inception. These begin under the free 

 margin of the gum, under plates that abut closely against the 

 teeth. These are usually very rapid in their course, evidently 

 for the reason that as soon as the free margin of the gum is 

 everted, a pocket is formed by aid of the plate, in which fer- 

 mentation can proceed to the very best advantage. It does 

 not seem that the beginning of this decay is often after the 

 eversion of the gum has uncovered the spot. Of course we 

 often see decays occur where clasps encircle the teeth that are 

 high up on the crown. Such must not be confounded with 

 those that begin at the margin of the cementum. 



