The earliest toy trains were made of lead and had no moving parts. Around 1875, technological advancements in materials and manufacturing allowed tin to be stamped, cut, rolled, and lithographed faster than ever before. Toy trains were revolutionized when Marklin, a German firm that specialized in doll house accessories, sought to create an equivalent toy for boys where a constant revenue stream could be ensured by selling add-on accessories for years after the initial purchase. In addition to boxed sets containing a train and track, Marklin offered extra track, rolling stock, and buildings sold separately. Electric trains followed, with the first appearing in 1897, produced by the U.S. firm Carlisle & Finch. Many modern electric toy trains contain sophisticated electronics that emit digitized sound effects and allow the operator to safely and easily run multiple remote control trains on one loop of track.