CAEIES. 91 



tainly more subject to caries and other destructive changes 

 than the incisors. The morbid process is sometimes slow, 

 and at others rapid. 



Two views have been maintained as to the origin of caries. 

 The one, that it is due to a chemical action on the teeth by 

 substances in the mouth ; and the other, that it depends on a 

 cause operating through the nerves and blood-vessels affecting 

 the nutrition of the tooth, and leading to its destruction, 

 gradual or quick. The latter is, in my opinion, the true 

 explanation of the origin of the disease. My readers must 

 not forget the reference I made in my last chapter to the 

 highly vascular and sensitive pulp, which sends delicate 

 branches into the numerous dentinal tubes. It is the pulp 

 with its prolongations which, when inflamed and affected by 

 exposure to air, or by heat and cold, becomes extremely 

 tender, and is the true seat of pain. Horses and all animals 

 suffer intolerably from toothache. They cannot eat, depress 

 their head, or lay it on the manger or side-post, and indicate 

 marked relief when the offending tooth is removed no easy 

 task, as we shall presently see. 



The caries, in the early stage, may lead to opacity, and 

 gradually to a dull brown or black hue of the enamel A 

 hole is formed, and the dentine then becomes diseased. It 

 seems often to exfoliate, and gradually to break up into its 

 constituent elements^ which are softened, and soon disintegrate. 

 It is the accumulation of putrefactive substances in the holes 

 of diseased teeth which induce great fcetor. 



The fang of the tooth may primarily become diseased, the 

 pulp is destroyed, and the tooth, being deprived of nourish- 

 ment, dies, and is rubbed down by the opposing tooth. This 

 is often the cause of fistulse of the face. An abscess forms in 

 the alveolus, the bone swells and softens, the matter points 

 to the surface and is discharged, so that, in the course of a 



