Shakti Gawain (2015). “The Shakti Gawain Essentials: 3 Books in 1: Creative Visualization, Living in the Light & Developing Intuition”, p.129, Mango Media Inc.
Florence Nightingale, Lynn McDonald (2004). “Florence Nightingale on Public Health Care: Collected Works of Florence Nightingale”, p.218, Wilfrid Laurier Univ. Press