DECAYED, EKAMEL SOFTENED. 145 



nates an offensive odor sui generis, which perhaps is 

 as much owing to the putrefaction of the saliva in the 

 cavity as to the decomposition of the dentine. The 

 decay progresses between the folds of enamel, and the 

 latter substance, notwithstanding its great density, 

 takes on the blackish tint of the dentine and becomes 

 sufficiently softened to allow of its being cut by a sharp 

 instrument. Sometimes even the planes of the enamel 

 dissolve, and then the cubic mass of the tooth becomes 

 so much decayed that it resembles a deep cavity, the 

 parietes of which are formed by the planes of enamel 

 laid bare by the caries. Sometimes caries attacks the 

 tooth on one of its four side surfaces; at other times 

 the root is attacked ; but wherever its primitive seat 

 may be, the blackish veins always extend into the den- 

 tine, and thus isolate the plies of enamel. 



" Carious teeth rarely preserve either their form or 

 volume. They become hypertrophied at their roots, 

 but the effect does not manifest itself until the disease 

 having undermined all the layers of dentine in its 

 course has penetrated the root. When the caries has 

 penetrated to the socket, the alveolo-deutal membrane 

 becomes irritated by the contact of decayed matter, 

 increases its secretion, and deposits a thick layer of 

 osseous matter in the circumference of the root of the 

 tooth, which concretes irregularly upon the normal 

 layers. The deposition does not, however, always take 

 place in the circumference of the root, for in some 

 cases it is only at isolated places that the secretion of 

 the alveolo-dental membrane occurs. Then the root 

 presents a succession of large osseous tubercles, which 

 bar the tooth in, rendering its extraction very difficult. 

 When the irritation has been from the first sufficiently 

 active to cause suppurative inflammation, the normal 

 7 



