[B] This investigation was undertaken at the request of the Council on Pharmacy and Chemistry. The following report, having been submitted to the Council, received its endorsement (see preceding report of the Council on Pharmacy and Chemistry, “So-Called Secretin Preparations”). It is well established that acid chyme in the duodenum is the normal stimulus to the secretion of pancreatic juice.[31] Interaction of the acid with the duodenal mucosa liberates into the blood stream a substance which, circulating through the pancreas, excites the latter to activity. This exciting substance has been termed “secretin.” It can be prepared artificially by macerating duodenojejunal mucosa in 0.4 per cent. hydrochloric acid, neutralizing the boiling mixture, and filtering. A few cubic centimeters of the filtrate injected into a vein produce invariably a powerful secretion of pancreatic juice.[32] That a “chemical messenger” is at the basis of the duodenal acid reflex has been proved by even more crucial experiments--transfusion (Wertheimer,[33] Enriquez and Hallion[34]), cross circulation (Fleig,[35] Matuso[36]), and perfusion of the isolated pancreas (Huston[37]). [31] Pawlow: The Work of the Digestive Glands, 1912. [32] Bayliss and Starling: Jour. Physiol. =28=:325, 1902. [33] Wertheimer: Compt. rend. Soc. de biol. =54=:475, 1902. [34] Enriquez and Hallion: Compt. rend. Soc. de biol. =55=:233, 363, 1903. [35] Fleig: Arch. internat. de Physiol., =10=:206, 1910. [36] Matuso: Jour. Physiol. =45=:477, 1913. [37] Huston: Ann. et bull. Soc. roy. de sc. méd. et nat. =70=:178, 1912. PROPERTIES OF SECRETIN _Prosecretin._--Secretin is soluble in water, yet a watery extract of intestinal scrapings is without action,[32] even after being submitted to acid treatment.[38] Starling therefore holds that secretin exists in the intestinal mucosa in an inactive form, as “prosecretin.” The content of the intestine in prosecretin decreases from the duodenum down, so that one is unable to demonstrate any prosecretin in the last 2-1/2 feet of the ileum. Prosecretin is insoluble in water, acetone, absolute alcohol or ether. Secretin, on the other hand, is readily soluble in water, normal salt solution and diluted alcohol (70 per cent.), but likewise insoluble in absolute alcohol and ether. [38] Starling: Lancet, London =2=:433, 1905.