106 EARLY DESTRUCTION OF THE TEETH. 



that they have never suspected the true cause to be 

 a chemical agent acting upon the external surface — 

 that wall of enamel and bone which surrounds and 

 protects the vital part of the tooth. 



Now, if for one moment we look at the mode in 

 which the enamel and bone of a tooth are formed, 

 and compare the growth of a tooth with that of 

 other bones, we shaU find no analogy existing 

 between them. On the contrary, we shall find a 

 striking resemblance between the growth of the 

 enamel and bone of a tooth, and that of inorganic 

 bodies ; both of which begin with a nucleus, and 

 become enlarged by a deposition of layers upon 

 their surface ; and also a striking resemblance to 

 each other in the manner of their destruction. 



Examine the rudiments of a young bone, and 

 what do we see? — vessels entering on aU. sides, 

 and in the centre a small bit of bone, of a loose 

 and spongy texture, which can be made quite red 

 by injection. We can trace the hardening through 

 every intermediate stage to that of a perfect bone, 

 the vessels of which, even in its most compact state, 

 are still easily demonstrable by the anatomist. 



Compare this now with the growth of a tooth, 

 and the result is different. Examine it at ever so 

 early a period, when only a speck of ossification is 

 discernible, and what do we see ? — a part complete in 

 its formation, having all the properties that belong 

 to the bone of a perfect tooth. 



The substance of which the bone of a tooth is 



