THE GERM THEORY OF CARIES. 167 



tinge, then brownish, and finally becomes black. This result 

 is brought about by the settling into, or the formation in, the 

 affected tissue of the black sulphurets ; as I was the first to 

 show. (See Report on Dental Chemistry, by Dr. H. A. Smith, 

 Transactions of the American Dental Association, 1874, 

 page 78.) 



We see these spots every day upon the sides of the molars, 

 in every stage of coloration, from ashy white to a deep black. 

 They are as apt to be on the otherwise smooth surfaces as in 

 the pits and grooves. They may occur on any of the teeth, 

 but are oftenest seen in the positions named. - The decays 

 that so often occur on the labial surfaces of the upper in- 

 cisors, are often, though not uniformly, of the same character. 



Those decays that occur just at the junction of the enamel 

 and cementum, in persons of middle age or past, also, occa- 

 sionally, in younger persons, in very many cases, seem to be 

 of the same character. Some irritation of the gum at the 

 immediate spot seems to be one condition of their beginning. 

 These also have some special characteristics not common to 

 other decays. If they are closely examined very early, in 

 their inception, it will be found that the cementum has been 

 removed and that the margin of the enamel has become 

 chalky. Soon after this, if the case continue to progress, the 

 gum, which till now was closely applied to the part, becomes 

 everted so as to expose the breach in the tooth. This often 

 becomes the seat of the most exquisite sensitiveness just at 

 the present stage of the process, which calls the attention of 

 the patient to the spot. Generally, however, nothing can be 

 seen by either patient or operator, except a slight eversion of 

 the gum, and the slight grooved appearance of the neck of 

 the tooth, which the operator is often puzzled to differentiate 

 from the normal form of the tooth. However, if he will 

 carefully press the gum away (and he will find this abnor- 



