On the medieval debate between the Catholic and Orthodox churches on this matter, see Jaroslav Pelikan, The Christian Tradition: A History of the Development of Doctrine, vol. 2, The Spirit of Eastern Christendom (600–1700) (Chicago: Univ. of Chicago Press, 1971), pp. 177–178. On the archaeological evidence pertaining to this dispute, see George Galavaris, Bread and the Liturgy: The Symbolism of Early Christian and Byzantine Bread Stamps (Madison: Univ. of Wisconsin Press, 1970).