Theodore Roosevelt (2015). “Theodore Roosevelt on Bravery: Lessons from the Most Courageous Leader of the Twentieth Century”, p.79, Skyhorse Publishing, Inc.
"Otto Dix, 1891-1969", exhibition catalogue, London: Tate Gallery, 1992, pp. 17 - 18; as cited by Roy Forward, in "Education resource material: beauty, truth and goodness in Dix's War", p. 9,