FORMATION AND GROWTH OF TEETH. 271 



admit of circulation within them ; yet they possess 

 life, and through that principle are in union with 

 the gum and jaw. A dead tooth, however pure 

 and perfect, when thrust into the socket of the 

 jaw, remains there no longer than would a peg of 

 wood or of metal. It causes inflammation and 

 pain, and is thrown out. 



It would be a difficult question for those who 

 consider life to be the result of organization to 

 solve, how a principle of life should exist for a 

 term of years, giving rise to a sympathy and union 

 with the jaw, in a part like the bone of a tooth, 

 which has neither what they call organization nor 

 any circulation of blood in it. Here we have one 

 of those inscrutable qualities of life which makes 

 physiology a science distinct from all others ; and 

 it is an example of there being adaptations far 

 more admirable than merely mechanical appli- 

 ances. 



But we were about to show how the different 

 portions of a tooth are formed. In the jaw of the 

 young animal a sac is discovered, which contains 

 the rudiments of the tooth. On opening the sac, 

 we think we see the tooth, but it is only a body of 

 the form of the crown of the tooth, and is soft to 

 the touch. This is called the pulp of the tooth ; 

 although pale at first, at a stated period it becomes 

 full of blood, and then the bone of the tooth begins 

 to be formed ; and now, on touching it, we can 

 lift from it a delicate shell, which is at once of the 

 form of the pulp, and of the perfect tooth. The 



