In 1947, the first full synthesis route for vitamin A was found by Dutch chemists, Jozef Ferdinand Arens and David Adriaan van Dorp. Later in 1947, a team headed by O. Isler also synthesized vitamin A using a method more suitable to produce commercial quantities. In 1913, Thomas B. Osborne and Lafayette Mendel had shown experimentally with rats that butter contained a factor responsible for growth development. Their work was confirmed (1913) by Elmer McCullum and Marguerite Davis who also identified a fat-soluble nutrient in butterfat and cod liver oil. It became known as vitamin A, and its chemical structure was determined in 1931 by Paul Karrer.«(Ref Arens and van Dorp, Synthesis of Vitamin A aldehyde, Nature 160: 187, 1947)