"I can't chew anything out of the pencil." This is how B. Traven described the authenticity of his novel characters in 1929. Others may be able to do that, but I cannot. I need to know the people I speak about. They must have been my friends, companions, adversaries, neighbors, or fellow citizens when I want to portray them. This postulate also applied when the author presented a story to film agent Paul Kohner in 1948, in which he describes the tale of a strange personality change. The case of the Mexican woman Mercedes Ortega Lozano, Traven assured, actually occurred as described; only the name of the affected person is his invention. Johannes Zeilinger analyzes the medical disturbances of this character, which has found its place in Mexican film history, and situates them within the context of Traven's biography.