1. McCurdy, J. T.: The Psychology of Emotion. Harcourt, Brace and Co., New York, 1925.
2. Henderson, D. K.: Oxford Medicine, Vol. 7, chapter 9, Oxford University Press, New York, 1936.
3. Strecker, E. A., and Palmer, H. D.: Oxford Medicine, Vol. 7, chapter 1, Oxford University Press, New York, 1936.
4. Henderson, D. K., and Gillespie, R. B.: Textbook of Psychiatry. Oxford University Press, New York, 1932.
5. White, W. A.: Outlines of Psychiatry. Nervous and Menal Disease Publishing Co., Washington, 1929.