FORMATION AND GROWTH OF TEETH. 273 



The difference between the bone and enamel 

 of a tooth, that is, between what is formed by 

 the pulp and by the sac, is shown by a very sim- 

 ple process. When a tooth is immersed in diluted 

 nitric or in muriatic acid, the enamel is dissolved 

 with effervescence, and is completely carried 

 away ; but when the earth of the bony part is 

 dissolved, it leaves behind it a cartilaginous mat- 

 ter, which constituted a part of the bone of the 

 tooth. In its chemical composition the bone of 

 the tooth resembles the bone of the skeleton, 

 though not strictly and anatomically, as it wants 

 the vascularity of true bone ; it is therefore, with 

 more propriety, called ivory. 



We have still to explain how the compound 

 teeth of the vegetable feeders are formed. Now, 

 if we comprehend the means employed in the 

 simple tooth, we shall have little difficulty in un- 

 derstanding this. The pulp is divided, and con- 

 sists of parallel layers joined below, but free 

 above, and with considerable interstices. These 

 divisions or processes of the pulp secrete the 

 ivory upon their surfaces, by which, of course, 

 plates of this dense material are formed on each 

 side of the soft processes or tongues of the pulp. 

 There will therefore be double the number of 

 plates of bone that there are processes of the 

 pulp. 



Each plate of bone must be covered or invested 

 with enamel. This is effected by folds or pro- 

 jecting processes of the capsule or sac, which, 



