1. Francois, M., Ann. Psychol., 28, 186 (1927).
2. Hoagland, H., J. Gen. Psychol., 9, 267 (1933).
3. Hoagland, H., Problems of Consciousness, edit. by Abramson, H. (Macy, New York, 1951).
4. Bull, H. B., An Introduction to Physical Biochemistry (Davis, Philadelphia, 1964).
5. Bell, C. R., J. Exp. Psychol., 70, 232 (1965).