Images from slide collections, 1970s. Top: molecular models of retinal; center left: bleached purple membrane in cuvette; center right: chemically modified preparations of purple membrane in centrifuge tubes; bottom left: Max Planck Institute of Biochemistry, 1974 (Copyright: www.luftbild-bertram.de); bottom right: electron micrograph of cell surface. By courtesy of D. Oesterhelt, Martinsried