Wilhelm Stekel, Nervöse Angstzustände und Ihre Behandlung; citing Freud in German, pp. 191-198
Wolfgang Schivelbusch, The Railway Journey: The Industrialization of Time and Space in the 19th Century, p. 78, citing Sigmund Freud as translated in English, "The Complete Psychological Work"
Bulletin of the Menninger Clinic, Volumes 16-18, p. 73
Paul C. Vitz, Sigmund Freud's Christian Unconscious, . 25
Aaron T. Beck, Gary Emery, Ruth L. Greenberg, Anxiety Disorders and Phobias: A Cognitive Perspective, 2005, ISBN 046500587X, p. 30
