Salt, Henry S. Animals' Rights: Considered in Relation to Social Progress, Macmillan & Co., 1894, chapter 1. He cited Spencer's definition of rights: "Every man is free to do that which he wills, provided he infringes not the equal liberty of any other man ... Whoever admits that each man must have a certain restricted freedom, asserts that it is right he should have this restricted freedom.... And hence the several particular freedoms deducible may fitly be called, as they commonly are called, his rights."