EARLY DESTRUCTION OF THE TEETH. 107 



composed is generated by a membrane called the 

 pulp. It is a compound of lime and animal matter, 

 which is thrown out by the pulp so as to enclose 

 itself within a wall of bone — not unlike the oyster, 

 which performs a similar office by enclosing itself 

 within its shell. I have only time to hint at this 

 similarity between the formation of the bone of the 

 tooth and the shell of the oyster, though I think it 

 worthy of further investigation. In both cases the 

 substance that forms the structure is generated and 

 thrown out by the pulp, and the surrounding walls 

 are thickened, enlarged, and strengthened by a 

 succession of layers. 



The outer part of the body of the tooth and its 

 fangs being thus formed, the tooth is prepared to 

 emerge above the gums, though there is yet a large 

 portion of the work to be accomplished; for per- 

 haps, upon the appearance of the tooth, not more 

 than one-third of the bone has been formed. The 

 pulp continues to the latest period of life to gene- 

 rate and throw bone upon the inner walls — one 

 layer being added to another, each portion perfect 

 in itself, neither receiving nor requiring further 

 nutriment, as other bones, and indeed as all orga- 

 nized bodies do ; and in this way the surrounding 

 walls increase in thickness, until the cavity that 

 contains the pulp frequently becomes in old age 

 almost fiUed up with bone. 



Now, the office of the pulp or bloodvessels within 

 the tooth is not to supply nutriment to the bone 



