Carl Ewald was a pioneer in the field of gastroenterology, and was a catalyst in making Augusta Hospital a center for pathological studies of digestion. Ewald is remembered for investigations of gastric secretions, and the introduction of intubation as a medical aid in gastric analysis. The eponymous Ewald tube is named after him, which is a gastric tube used for emptying the contents of the stomach.
With Ismar Isidor Boas (1858-1938), he developed a standard "test meal" for gastric analysis. This involved a process in which various foods were given to a patient, and followed by analysis of gastric juices at scheduled intervals. Among his published works are "The Diseases of the Stomach" and "Lectures on Digestion", which have both been translated into English. For many years Ewald was editor of the Berlin klinische Wochenschrift, as well as librarian to the Berlin Medical Society.