Henry David Thoreau, Barry Andrews (2005). “True Harvest: Readings from Henry David Thoreau for Every Day of the Year”, p.29, Unitarian Universalist Association of Congregations
"Out of the Jungle" (1967); as quoted in "Compassion, the Ultimate Ethic: An Exploration of Veganism" by Victoria Moran, Wellingborough: Thorsons, (p. 31), 1985.