The Blood Covenant 

Apart from, and yet linked with, the explicit proofs of the rite of blood-covenanting throughout the primitive world, there are many indications of the root-idea of this form of covenanting; in the popular estimate of blood, and of all the marvelous possibilities through blood-transference. These indications, also, are of old, and from everywhere.
To go back again to the earlier written history of the world; it is evident that the ancient Egyptians recognized blood as in a peculiar sense life itself; and that they counted the heart,-as the blood-source and the blood-centre,-the symbol and the substance of life. In the Book of the Dead, the deceased speaks of his heart,-or his blood-fountain,-as his life; and as giving him the right to appear in the presence of the gods: "My heart was my mother; my heart was my mother; my heart was my being on earth; placed within me; returned to me by the chief gods, placing me before the gods"