Later, the wear of the teeth gives no good idea of the age, because so much depends upon the kind of food the animal eats, whether it is hard or soft. When a dog is fed on bread and gravy or meat, the teeth will show little or no signs of wear when he is two or three years old, while the incisor teeth of another dog of the same age will commence to become blunted if biscuits form the staple food. The teeth become still more worn if a large number of bones are given as a part of the diet. And again, dogs who are always playing with and carrying stones often wear the incisor teeth right down to the gums, and the tusks become worn in the course of a few years. As a rule, if a dog is fed on a mixed diet, as bread and vegetables, soaked biscuits, etc., and not given many bones, and is not allowed to carry stones, then the teeth (incisors and tusks) preserve their shape and position until the fourth year. But by this time the teeth have lost their _very_ white colour, and have become of a palish yellow colour. As the dog advances in years the teeth become still more yellow, besides becoming coated with tartar just above the neck of the tooth, if they have not been occasionally scaled. The tusks, too, now become blunted, and to some degree are altered in position, being inclined to take a more outward direction. It is, therefore, an easy matter to distinguish between an old and a young dog. The teeth of dogs that are pig-jawed, and those that are undershot like bulldogs, do not, of course, wear to the same extent as when the incisors meet, forming an even mouth.