167 



of all the structures that enter the composition of 

 the tooth. In proportion to the vascularity, maybe 

 estimated the disposition to assume disease; and when 

 it is further remembered that the crusta petrosa being 

 the external, is the most exposed portion of the tooth, 

 and that any wrenching action, or other violence, 

 would first affect this part, the dullest comprehension 

 will perceive why the crusta petrosa is likely to be 

 the primary seat of caries. Enamel is not subject to 

 caries, nor is it otherwise involved than by being 

 deprived of its supports, and chemically acted upon 

 by the decomposed matters with which it is in con- 

 tact. The ivory, however, may, in exceptionable 

 cases, be the original seat of the affection ; and 

 when decay has commenced, this part of the tooth 

 is speedily diseased. When caries begins, there is 

 only partial death of the tooth ; but the portions 

 which retain their vitality and are becoming affected, 

 cause excruciating fits of agony. Before anything 

 can be perceived by manipulating the molars, the 

 animal may exhibit frequent slight fits of illness, 

 being occasionally dull — off its feed — sluggish at its 

 work — soon fatigued — resting the head on the man- 

 ger, and displaying symptoms of transcient attacks 



