Historically, doctors thought that genetics, anxiety, or even spicy foods caused stomach ulcers. While these may worsen the pain of an ulcer, scientists now believe that the gastric ulcer is caused by a bacterium called Helicobacter pylori. Researcher Barry J. Marshall (1951-) observed that many ulcer patients had these bacteria present in their systems. In 1984 Marshall designed an experiment to determine whether there was a link between Helicobacter pylori and stomach ulcers. He consumed a large amount of the bacteria and waited. After 10 days, he developed ulcers. Marshall shared the 2005 Nobel Prize in Physiology or Medicine with J. Robin Warren (1937-) for their discovery of the bacterium Helicobacter pylori and its role in gastritis and peptic ulcer disease.