FORMATION OF DENTINE. 241 



mouth of a boy eleven years of age, and of which an exact 

 representation of a microscopic view of it is annexed. (Fig. 

 66.) The tooth had ached violently for several days pre- 

 vious to its extraction, from which circumstance he was 

 induced to believe that the vessels of the pulp were highly 

 injected, and to satisfy himself upon the subject, he soon 

 after its removal split it open with a strong pair of ex- 

 cising forceps. As was anticipated, the vessels of the pulp 

 were filled with red blood, and on examining the half of 

 the tooth in which this had remained, through a micro- 

 scope, a number of vessels within the very substance of the 

 bone, charged with this fluid, were distinctly seen." The 

 crown is represented as decayed. 



Formation of the Dentine. The ossification of a tooth, it 

 is well known, commences on the surface of the pulp, and 

 according to the experiments of Mr. Hunter, from feeding 

 animals on madder, this ossific matter is laid layer within 

 layer, from the surface to the centre, till the tooth is com- 

 pleted, the pulp retiring and diminishing as ossification 

 advances. 



The incisors begin to ossify by three points, the cuspids 

 by one, the bicuspids by two, and the molars by three, 

 four, or five, according to the number of projections or 

 tubercles upon their grinding surface. The crown of the 

 tooth being formed, the roots are next observed to be de- 

 veloped, and their number always previously indicated by 

 the number of distinct vessels and nerves going to the 

 pulp. 



This view of the formation of dentine has been termed 

 the excretion theory. The later researches of Mr. Nasmyth 

 give another view of the subject ; observing the similarity 

 of structure between the pulp and dentine, that each pos- 

 sessed the cellular or reticular arrangement, (in his own 

 comprehensive language) he remarks, u My theory, indeed, 

 is most simple, the cells of the pulp are converted into 

 ivory cells by the deposition within them of earthy salts, 

 and the cells so converted, with their nuclei, are the perfect 

 ivory ; moreover, the nuclei assume a peculiar arrange- 

 16 



