Mark Twain (2014). “Mark Twain on Common Sense: Timeless Advice and Words of Wisdom from America's Most-Revered Humorist”, p.53, Skyhorse Publishing, Inc.
David Wolfe (2013). “Longevity Now: A Comprehensive Approach to Healthy Hormones, Detoxification, Super Immunity, Reversing Calcification, and Total Rejuvenation”, p.20, North Atlantic Books