210 THE TEETH AS INDICATORS OF AGE. 



dilating the progress of wear." Such teeth would soon 

 wear out, for there is as much difference in the density 

 of cement and enamel as between cartilage and bone. 



The obliteration of the mark may be hastened in a 

 small or medium-sized tooth by the friction of one that 

 is abnormally large, while a stunted or dead tooth may 

 never lose its mark. 



The more upright the teeth the faster they wear. It 

 is said that the crowns will be worn to the extent of a 

 quarter of an inch between the fifth and sixth years 

 (when they are .most upright), while only about that 

 quantity of material will wear away between the twen- 

 tieth and twenty-fifth years. 



A horse's food is a matter also to be taken into ac- 

 count. The mastication of grass, carrots, turnips, 

 potatoes, bread, &c., does not cause much wear to the 

 teeth. However, when grass is procured by grazing, 

 the incisors suffer much friction caused, not by the 

 grass, but by the teeth grinding one another, for they 

 meet edge to edge, and are employed in this occupa- 

 tion for hours, whereas a "feed" of corn is shelled in 

 a few minutes. In the former case the incisors suffer 

 great friction ; in the latter, the grinders. Again, it is 

 said that "horses fed on salt marshes, where the sea- 

 sand is washed among the grass, or on sandy plains or 

 meadows, are affected by the increased friction of their 

 teeth." But no matter how soft a horse's food may 

 be, if he is addicted to the vice called " crib-biting," 

 his teeth may be ruined before those of the corn-fed 

 horse have even lost their marks. 



Several trade tricks are also to be noted. Of "bish- 

 oping," Prof. Youatt says : 



" Dishonest dealers resort to a method of imitating 



