The comparative student must also give careful consideration to what are called the eschatologic doctrines, the beliefs concerning posthumous happiness, salvation, and damnation, not only of the Judaic, but also of the Hellenic, Anatolian, and Egyptian religions: and especially to those of the Hellenic, for it was they that were most widely known in the area of the Greco-Roman world, and modern theory has at times endeavoured to trace back the apocalyptic literature of Christianity to Hellenic sources.[63.1] The investigation would demand a careful study of the Eleusinian and the Orphic Mysteries, in both of which we find the pregnant idea that salvation after death depended {64} on a religious act of faith or on a mystic communion with a divinity that might be attained on earth by a sacrament or other liturgical means: and the inquiry will include the question how far in these earlier systems the doctrine of salvation by faith was actually blended with any admixture of the ethical doctrine of salvation by works. And the problem, like many others in the scientific study of religion, will be found to concern philosophic as well as religious history. The ideas attaching to sacrifice in the Mediterranean world have long been recognised as a vital subject of inquiry for the comparative science; and both the lower and the higher anthropology can contribute much that is essential to the full understanding of the evolution of the Christian doctrine concerning the divine sacrifice and the Holy Communion. I need not here enlarge on this subject, even by way of mere illustration, for I have already dealt with it, however inadequately, {65} in a former paper:[65.1] it is an intricate and fascinating theme and invites further research.