1. M. Summers: “The Geography of Witchcraft”, New York, University Books, 1958, pp. 253–256.
2. V.P. Wasson and R.G. Wasson: “Mushrooms, Russia and History”, New York, Pantheon, 1958, Vol. 2, pp. 215–286.
3. L.J. West (Ed.): “Hallucinations”, New York, Grune & Stratton, 1962.
4. N. Kleitman: “Sleep and wakefulness”, Chicago, University of Chicago Press, 1963, p. 229.
5. E.J. Murray: “Conflict and repression during sleep deprivation”, J. Abnorm. Soc. Psychol. 59, 1959, pp. 95–101.