Feng Su Tung (Penetrating Popular Ways), by Liu Hsiang (c. 77-6 BC) of the Han dynasty recounts that the first Ch'in emperor would kill a dog and smear its blood at the four gates to ward off evil spells. This was behind the later custom of killing a white dog in the first lunar month and smearing its blood on the doors of one's house.
「風俗通」又說，秦始皇殺狗，以血塗四門，以禦蠱災，所以後人也有在正月時殺白犬，把血塗抹在門戶上的習俗。