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 (© www.luftbild-bertram.de ); bottom right: electron micrograph of cell surface. By courtesy of D. Oesterhelt, Martinsried.