Although Wirsung1 as early as 1645 had discovered the pancreatic duct and described the fluid which flows through it and DeGraaf2 in 1664 had collected some of this fluid, using a wild duck's quill for a cannula, present knowledge of the physiology of the external function of the pancreas came largely as a result of the work of four investigators in the late part of the nineteenth and the early part of the twentieth century, namely, Bernard,3 Pavlov4 and Bayliss and Starling.5 Bernard in 1856 showed that pancreatic juice is essential to digestion. Pavlov in 1902 demonstrated the existence of pancreatic enzymes, and in the same year Bayliss and Starling investigated the factors concerned in the secretory stimulus of the pancreas and assigned the important role to a humoral factor, which they named secretin. McClure6 has enumerated as follows the important physiologic facts, which