After Hans von Euler-Chelpin’s early purification of NAD and Conrad Elvehjem’s discovery of nicotinic acid as the nutrient that prevented pellagra, Arthur Kornberg studied the way that NAD is made in the body. By this time, methods for the purification of proteins and co-enzymes had advanced to the point that scientists could purify all the components that he/she thought would be needed for a reaction and then test his theory by combining the purified components and looking for evidence that the reaction happened. In Kornberg’s experiments, he purified the components needed for the NAD-generating reaction from yeast, and combined them in an experimental set-up to demonstrate that they were responsible for creating NAD.