?-1779

French biologist who investigated the chemical properties of blood. Roulle was the first to investigate the chemical components of vertebrate blood, discovering sodium chloride (salt), potassium chloride, and sodium carbonate to be present in the liquid portion of blood (the plasma). This led eventually to the discoveries that blood plasma resembles not only other bodily fluids, but also seawater in its chemical composition. Eventually, knowledge of blood chemistry became a powerful medical diagnostic tool.