Robert M. Sapolsky (2004). “Why Zebras Don't Get Ulcers: The Acclaimed Guide to Stress, Stress-Related Diseases, and Coping - Now Revised and Updated”, p.10, Macmillan
Sir Humphry Davy (1840). “Salmonia: or, Days of fly-fishing; in a series of conversations: with some account of the habits of fishes belonging to the genus Salmo. Consolation in travel, or, The last days of a philosopher”, p.350