EARLY DESTRUCTION OF THE TEETH. 109 



that nutriment cannot be derived from a membrane 

 after it has ceased to exist. 



When the grinding surface of a tooth has been 

 formed by the first layer of bone thrown out by the 

 pulp, a deposition of enamel begins upon the highest 

 parts of the surface, and which will ultimately form 

 the most prominent parts of the crown of the tooth. 

 At the commencement, therefore, there will be 

 several isolated spots of enamel that will gradually 

 increase in size and thickness, till at last, in a well- 

 formed tooth, they coalesce, so as to constitute a 

 continuous covering over that portion which is 

 necessarily exposed for the purpose of grinding the 

 food. In the great majority of cases, however, a 

 perfect union of the several portions of the enamel 

 does not take place. The secreting membrane 

 furnishes an abundant supply, up to the very period 

 when the isolated portions of this substance are 

 apparPMtly upon the point of uniting ; but in many 

 instances a perfect union does not take place — the 

 isolated portions continue to increase in thickness, 

 but they do not spread out and incorporate so as 

 to produce a level surface, a continuous covering, 

 over every other portion of the bone. "Whether 

 this defect can be traced to the compound forming 

 the enamel being of a less fluid nature, in con- 

 sequence of its containing perhaps an over-pro- 

 portion of lime to the animal matter, is a question 

 to be solved. It is no doubt a constitutional 

 defect — one over which, I fear, we have no control. 



V 



