Numerous investigators1 observed the occurrence of peptic ulcers in animals following the diversion of duodenal secretions, and attributed the development of these lesions to the loss of the neutralizing influence of the alkaline duodenal fluids on the acid gastric juice. Their conclusions were based on the work of Boldyreff,2 who promulgated the theory that gastric acidity was regulated by the regurgitation of the contents of the duodenum into the stomach. Boldyreff noted that the pancreatic juice was more alkaline than any of the other secretions that were present in the duodenum, and he believed that it was the chief factor in the neutralization of the acid secreted by the stomach. The results of the investigations of MacLean and Griffiths,3 McCann,4 and Yesko,5 however, indicated that changes in gastric acidity did not depend on the regurgitation of alkaline duodenal juices. Recent determinations6 of the gastric