n the beginning days of 35mm photography, you could not go to a store and buy a roll of film. Initially, all 35mm still photographers used reloadable metal cassettes that had to be individually loaded with film cut from bulk rolls (and the film end had to be cut with a suitable leader for the take-up spool). By the late 1920s you could buy pre-spooled 12- 18- and 36-exposure lengths of film in foil packets and simply insert them into the cassettes, a convenience that proved to be very popular.