1. Crawford, J. P.: Re-search and Research in Psychopathology. Guy's Hosp. Gaz. 69, 48, 1955.
2. Henderson, D. K., and Gillespie, R. D.: A Text-Book of Psychiatry. Oxford Medical Publications. 1936.
3. Hargreaves, G. R. (Nuffield Professor of Psychiatry, University of Leeds, England.): Personal communication, 1960.