H. C. Trumbull 
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‘