Bishop, Paul (2006). «2: Hermann Hesse and the Weimar Republic». En Karl Leydecker, ed. German Novelists of the Weimar Republic:Intersections of Literature and Politics(en inglés). Boydell & Brewer. p. 47. ISBN1571132880. Consultado el 24 de septiembre de 2013. «[...] in May 1916 he began psychotherapy [...] Within the first month, Hesse attended twelve sessions with Dr. Lang, and between June 1916 and November 1917 he completed a further sixty sessions».