Contrast materials in these early years included bismuth-filled capsules covered with celluloid to prevent them from dissolving in the digestive tract, gas or air introduced into the colon, a spiral wire introduced into the oesophagus, an oesophageal sound filled with mercury or lead shot, and bismuth subnitrate in a suspension or mixed with food. However, by about 1910, barium sulphate had, at least in America, replaced bismuth preparations as a contrast material for the GI tract.