That the door or the threshold is the seat of a tutelary spirit or genius is a belief familiar enough in folk-lore: the door must not be banged,[8] nor wood chopped on the threshold,[9] for fear of disturbing him. He is apt to disappear, taking the luck of the house with him, if a cat is maliciously buried under the door-sill,[10] or if human hair is so buried.[11] The importance of the door as a possible entrance for evil spirits, or exit for lucky ones, is manifest in many customs, _e.g._, nailing a horse-shoe on the door or sticking a knife into the door, and in such beliefs as that when a door opens (apparently) of itself, a spirit is entering. Whether the Italian spirit of the doorway, who in origin is indistinguishable from the similar though nameless spirits to be found elsewhere, was capable by his own unaided efforts of raising himself to the rank of a god, is matter for speculation. What is clear is that he had not the chance: the introduction of Greek polytheism into Italy promoted him without exertion on his part. As, thus far, I have assumed a distinction between "gods" and "spirits," and have also assumed that a belief in the latter may exist without polytheism and precede it, it will be well here to state explicitly the distinction. And that I may not be suspected of drawing the distinction so as to suit my own ends, I shall here borrow from a standard work, Chantepie de la Saussaye's _Religionsgeschichte_ (i. 90). De la Saussaye notes five characteristics involved in the conception of "gods." First, they are related to one another as members of a family or community, and as subject to one god, who is either lord of all, or at any rate _primus inter pares_. Second, with the growth of art, they are represented plastically and are made in the image of man. Third, as ethics advance, moral benefits are associated with their worship. Hence, in the fourth place, the gods are conceived as personal, individual beings, ideally good and beautiful. Finally, the human intellect demands that the relations of the gods to one another and to Nature should be co-ordinated into a system, and so theogonies and cosmogonies are invented.