These lines indicate an approach at least to the idea of mental as well as material purity; and Cicero in his _ius divinum_ in the _de Legibus_[369] actually reaches that idea: "caste iubet lex adire ad deos, animo videlicet, in quo sunt omnia: nec tollit castimoniam corporis," etc. But this is the language of a later age, and does not reflect the notions of the old Roman, but rather those of the religious philosophy of the Greek. The personal purity which the Roman rule required was a survival from a set of primitive ideas, closely connected with taboo, which we are only now beginning to understand fully. They are common to all or almost all peoples who have made any progress in systematising their sacrificial worship. As Dr. Westermarck has recently expressed it,[370] "they spring from the idea that the contact of a polluting substance with anything holy is followed by injurious consequences. It is supposed to deprive a deity or holy being of its holiness.... So also a sacred act is believed to lose its sacredness by being performed by an unclean individual." And in the next sentence he goes still farther back in the history of the belief, pointing out that a polluting substance is itself held to contain mysterious energy of a baneful kind. But I must leave this interesting subject now; the story of the evolution of the habit of cleanliness from these ancient ideas will be found in the thirty-ninth chapter of his _Origin and Development of Moral Ideas_. Coming next to the act of sacrifice itself, it is needless to say that the victim must be as exactly fitted to please the deity--if that be the right way to express the obligation--as the priest who sacrificed it. It must be of the right kind, sex, age, colour; it must go willingly to the slaughter, adorned with fillets and ribbons (_infulae_, _vittae_), in order to mark it off from other animals as holy; in the case of oxen, we hear also of the gilding of the horns, but this must have been costly and unusual.[371] All these details were doubtless laid down in the _ius divinum_, and in later times, when the deities dwelt in roofed temples, they were embodied in the _lex_ or charter of each temple.[372] I do not need to go into them here minutely; for my present purpose, the elucidation of the meaning which the Romans attached to sacrificial worship, it will be sufficient to point out that all victims, so far as we know, were domestic animals, and in almost all cases they were valuable property (_pecunia_), such as belonged to the stock of the Latin farmer, ox, sheep, pig, varying according to age and sex. Goats were used at the Lupercalia, and a horse was sacrificed to Mars, as we have seen, on October 15, and at the Robigalia in April a red dog was offered to the spirit of the mildew. But though time forbids me to explain all these rules, a careful study of the evidence for them is most useful for any one who wishes to understand the influence of the