The American physician George P. Cammann invented the binaural flexible stethoscope. By 1852 Cammann "had developed a stethoscope with flexible tubing (spirals of wire covered with silk, later rubber, or as he called it caoutchouc), ivory ear-pieces, and spring cross piece to hold the ear-pieces in place. The formal announcement of the stethoscope appeared in 1855" (McKusick, Cardiovascular sound in health and disease [1958] 13).