The dog has always been considered man ’ s best friend. Always known for being particularly faithful in watching over children, he also has his place by the fireside, in the farm, and beside the hunter in forest or blind. He is easy to train, works hard, and often does wonderful jobs. And in the frozen polar regions he was once the chief power, before being largely replaced by the plane. Because he howls ( 嚎叫 ) in the presence of coming death, the dog was once thought to have supernatural powers and believed to be capable of seeing gods and ghosts that can ’ t be seen by men. Actually, the basis for these beliefs lies in the dog ’ s sensitivity to people ’ s feelings and his good hearing ability and sense of smell, which enable him to detect signs hidden from human observation. His record of saving lives is amazing, for he often gives warning of fire and other dangers not noticed by his master. The dog ’ s major contribution, however, has been to medical research. Both his diet and his structure are similar to those of the human being, and so he has been the subject of many experiments. Open-heart surgery has been made possible largely because of the dog. But his sacrifice has benefited his own species as well by keeping it from rabies ( 狂犬病 ), mental disorder and other diseases.