Mysteries of nature.

This article examines a group photograph of the Psychiatry and Neurology section of the 66th Meeting of the Society of German Natural Scientists and Doctors in Vienna, 24-30 September 1894 which Sigmund Freud attended. The society's origins in Naturphilosophie are indicated and a number of the participants are identified on the photo. They and the events at the conference are related to Sigmund Freud's work at the time and to his gradual abandonment of anatomy and of heredity and degeneration as significant aetiological factors in the neuroses. Philosophical problems, such as how phenomena should be described and how 'nature' is conceptualized, are also considered in the light of their implications for Freud's life and thought at that period.