STRUCTURE, DECAY, AND PRESERVATION OF THE TEETH. 287 



as in onamol we have a higlily calcified iiiorgauie substance 

 with no indication of physiological activity. 



Tlie principal evidence of vitality shown by dentine is its 

 great sensibility when diseased ; the presence of protoplasm 

 in the tubular structure, and the fact that nerve filaments 

 are found in it, derived both from the pulp and the perios- 

 teum, give reasons for this. 



The vital charaeteristics of the dentine are most marked 

 in intra-uterine life, and depend therefore on the health of 

 the parent. Defects arising from this cause are added to 

 by improper feeding in early life ; but injury done at this 

 period remains invisible, and only comes into prominence 

 years afterwards, when the tooth appears above the gum. 

 The various congenital defects of structure duo to imperfect 

 formation of the dental tissues were shown to be the 

 principal predisposing causes on which decay of the teeth 

 depends. 



The conditions in the mouth which favour chemical 

 activity, and the physiological activity of tlie tissues and 

 ferment germs found there, were then reviewed. In health 

 the tendency to disintegration is resisted, but morbid con- 

 (Htions favour the action of the disintegrating forces. The 

 contrast, between the normal transformation of the teeth in 

 old age, leading to tlieir ultimate death and falling out with 

 absorption of their supporting bony framework, with the 

 premature decay and disintegration from caries in earlier 

 life, was pointed out, the one a physiological but the other 

 a pathological process. 



Caries, or decay of the teeth, was described as a gradu- 

 ally progressive disintegration of the enamel and dentine, 

 beginning always at the surface, generally in uneven rough 

 places where food might lodge ; the macroscopic and micro- 

 scopic appearances were pointed out, more particularly the 



B B 



