The dog has always been considered man's best friend. Always noted for being particularly faithful in watching over children, he also has his place by the fireside. in the cow pasture, on the sheep range（放牧区）, and beside the hunter in forest. He is easy to train, works hard, and often performs astonishing feats.And in the frozen polar regions he was once the principal motive powel before being lately dis-placed plane and helicopter.
　　Because he howls or whines in the presence of impending death , the dog was once thought to have supernatural power and believed to be capable of seeing gods and ghost invisible to men.Actually, the basis for these beliefs lies in the hound' s sensibility to people' s feelings and his superior hearing ability and sense of smell，which enable him to detect signs hidden from human observation.His record of saving lives is outstanding, for he often gives warning of fire and other dangers not noticed by his master.
　　The dog's major conribution , however, has been to medical research. Both his diet and his structure are comparable to those of the human being, and so he has been the subject of countless demonstra-tions and experiments. Open-heart surgery has been made possible largely because of the dog. But his sacrifice has repaid his own species as well by safeguarding it from rabies（狂犬病）distemper, and other diseases.