THE ALVEOLO-DENTAL PERIOSTEUM. 165 



lence, although we are not always able to trace it to 

 such a cause. Inflammation of the alveolo-dental peri- 

 osteum, especially where it surrounds the root or roots 

 of a tooth, would tend to this result. Other causes 

 may produce the same effect. Indeed, whenever or 

 however effected, when the nutrition of any part of a 

 tooth ceases, decay is likely to follow. When caries 

 begins from within, it is due to cessation of nutrition, 

 arising perhaps from disease of only a part of the cen- 

 tral pulp of the tooth. If from without, it arises from 

 the periodontal membrane where it meets the gum. 



" Caries of the cervix (neck) of the tooth is much 

 more common than it is in the root ; still it does not 

 occur in more than one horse in five hundred. The 

 question will naturally be asked, To what does this 

 tendency to decay belong ? Under such circumstances 

 are we not forced to the conclusion that it must de- 

 pend either upon a defective structure of the tooth, or 

 that the dentine, enamel, and cement are dispropor- 

 tionately developed, or that one of them is defective in 

 its parts? Another and perhaps the most frequent 

 predisposing cause of caries of the neck of the grinder 

 teeth is that food becomes impacted between them. 

 Its decomposition may not only affect the teeth, but 

 the alveolar processes also." 



The professor believes that caries of the crown of a 

 tooth is generally caused by the horse biting on a stone 

 or piece of metal during mastication. If the stone is 

 lodged in the cavity of the infundibulum, the pulp of 

 the tooth may be injured, for, to use the professor's 

 words,' " the thickness of the tooth between the upper 

 part of the pulp-cavity and the bottom of the deepest 

 infundibula is not very great." 



