Intrinsic factor

Since patients with pernicious anemia had a characteristic lack of hydrochloric acid in their gastric juice, Castle suggested that it was some component of normal gastric juice. He called it intrinsic factor, and it aids in the absorption of the vitamin preventing pernicious anemia.
 William Bosworth Castle United States 1929 Intrinsic factor

Since patients with pernicious anemia had a characteristic lack of hydrochloric acid in their gastric juice, Castle suggested that it was some component of normal gastric juice. He called it intrinsic factor, and it aids in the absorption of the vitamin preventing pernicious anemia.