Pancreatic secretion was first studied at The Mount Sinai Hospital by Crohn in 1912, but measurements of pancreatic enzymes in duodenal aspirate or feces were found unhelpful in diagnosis. Such pancreatic tests fell into disuse because of advances in radiology of the biliary tree in the 1920s. Once extracts of secretin and cholecystokinin-pancreozymin became available from Sweden in the 1930s, it became possible for the biochemist Franklin Hollander and the surgeon David Dreiling to develop pancreatic secretion tests into practical procedures for the diagnosis of benign and malignant diseases of the pancreas and biliary tree, and produce physiological studies of the mechanisms of ion transport. With more purified hormones, it became possible to measure maximum (alkaline) bicarbonate output of the pancreas analogous to the maximal acid response of the stomach to an augmented histamine test, and to determine whether patients with duodenal ulcer had decreased neutralization of gastric acid in the duodenum. Clinical studies were also directed to the pathophysiology of acute relapsing and chronic pancreatitis and carcinoma. However, advances in imaging and endoscopy have now shifted the thrust of pancreatology.