Healthy teeth depcnd mainly on healthy digestion, and on cleanly habits as regards the teeth. They must, of course, be confined to the purposes for whick they are designed. If they are employed for the purpose of cracking nuts, biting thread, unscrewing needlecases, or turning the stopper of a smelling-bottle; it the mouth is used as a kind of portable for a tool-chest, in which a pair of scissors, a knife, a vice, a corkscrew, or any other instrument, may be found at the time of needthen serious and irretrievable injury will eventually be done to the enamel of the teeth, which no healthiness of digestion nor cleanliness of habit will avail to remedy.