very close to the later conceptualised enzyme. In 1653 William Harvey described the intestines in terms of their length, their blood supply, the mesenteries, and fat (adenylyl cyclase). In 1823 William Prout discovered hydrochloric acid in the gastric juice. In 1895 Ivan Pavlov described its secretion as being stimulated by a neurologic reflex with the vagus nerve having a crucial role. Black in the 19th century suggested an association of histamine with this secretion. In 1916 Popielski described histamine as a gastric secretagogue of hydrochloric acid. William Beaumont was an army surgeon who in 1825 was able to observe digestion as it took place in the stomach. This was made possible by experiments on a man with a stomach wound that did not fully heal leaving an opening into the stomach. The churning motion of the stomach was described among other findings. In the 19th century it was accepted that chemical processes were involved in the process of digestion. Physiological research into secretion and the gastrointestinal tract was pursued with experiments undertaken by Claude Bernard, Rudolph Heidenhain and Ivan Pavlov. The rest of the 20th century was dominated by research into enzymes. The first to be discovered was secretin by Ernest Starling in 1902, with ensuing results from John Edkins in 1905 who first suggested gastrin with its structure being determined in 1964. Andre Latarjet and Lester Dragstedt found a role for acetylcholine in the digestive system. In 1972 H2 receptor agonists were described by J. Black, that block the action of histamine and decrease the production of hydrochloric acid. In 1980 proton pump inhibitors were described by Sachs. In 1983 the role of Helicobacter pylori in the formation of ulcers was described by Barry Marshall, and Robin Warren. Art historians have often noted that banqueters on iconographic records of ancient Mediterranean societies almost always appear to be lying down on their left sides. One possible explanation could lie in the anatomy of the stomach and in the digestive mechanism. When lying on the left, the food has room to expand because the curvature of the stomach is enhanced in that position. See also Ulcerative colitis Abdominal internal oblique muscle References Organ systems Metabolism