THE TEETH. 73 



[The following remarks may be made upon the pathology 

 of the teeth. Permanent teeth which have fallen out are 

 sometimes replaced by a third dentition ; but it must not be 

 forgotten that the milk teeth occasionally remain beyond their 

 time, and care must be taken not to confound a second tooth, 

 late in its eruption, with a third. Teeth which have been ex- 

 tracted may be replaced (in fifteen months a canine tooth which 

 had been extracted from the upper jaw was perfectly firm 

 again). An abnormal development of the teeth takes place 

 particularly in the ovarium, but also elsewhere. Fractures of 

 the teeth may be re-united when they occur within the alveoli, 

 by imperfect dentine or cement. Regeneration of the worn 

 down parts takes place only in animals (Rodents, e. g.) 

 in which the teeth constantly grow. Hypertrophy of the ce- 

 ment (the so-called exostosis), deposits of dentine in the walls 

 of the pulp cavity and ossification of the pulp itself, are ex- 

 ceedingly common, and result from chronic inflammation of the 

 periosteum and pulp. A partial disappearance of the fang is 

 not uncommon. Necrosis of the teeth takes place when the 

 periosteum has been stripped off, or the pulp has died. The 

 teeth become rough and dark, even black, and finally fall out. 

 The nature and causes of dental caries are doubtful. It 

 attacks living and false teeth (Tomes), and always begins on 

 the exterior, from Nasmyth's membrane (Ficinus), whence the 

 fluids of the mouth have been supposed to have considerable 

 influence upon it ; it does not follow, however, that one living 

 tooth may not be more disposed to it than another, being ren- 

 dered less capable of resistance either by its chemical composi- 

 tion, or by the mode of its nutrition. Caries, however, is as- 

 suredly not a simple solution of the salts by the oral fluids, but 

 a solution accompanied by a putrefactive decomposition of the 

 organic elements of the tooth, which becomes covered with 

 infusoria and fungi ; in fact, according to Ficinus's observations, 

 the latter growths would appear to play the more important 

 part, inasmuch as the decay of the teeth usually commences in 

 those localities in which undisturbed opportunity is given to 

 these organisms to develope, as in the cracks and pits of the 

 enamel, in the depressions of the molar teeth, in the clefts be- 

 tween the teeth, but not where the dentine is otherwise exposed, 

 as on the masticating surface, in filed places, &c. The usual 



