Early in our study of the physiology of the biliary tract we were impressed with the considerable influence that the mechanism at the distal end of the common bile duct exerts, not only over the discharge of bile from the common duct into the duodenum but also over the gallbladder. In a previous article it was shown by one of us1 that the control over the distal end of the common duct is one of the necessary factors for the collection of bile by the gallbladder. This article, one of a series of papers on the liver and biliary tract which have appeared from this department of surgery during the last five years, will report observations concerning some factors involved in the regulation of the flow of bile into the duodenum. A method of the regulation of the flow of pancreatic juice into the duodenum will also be described. The