19th century gallstone from a horse. Section through a large gallstone that was removed from the intestines of a horse during the 19th century. Gallstones are bodies formed by the hardening of deposits of cholesterol and bile salts. The concentric rings that can be seen were formed as more and more deposits accumulated over time. Photographed in the museum of the National Veterinary School of Alfort, Maisons-Alfort, France.