The duct common to the liver and the pancreas opens into the second part of the duodenum. The organs which produce bile and pancreatic juice are comparatively remote from the place where their secretions come into contact with the food. By what mechanism are they thrown into activity when the assistance of their secretions is required? As in the case of the stomach, the agent is a hormone, a chemical messenger. The hormone, termed “secretin,” is formed by the cells of the mucous membrane of the duodenum when acid comes in contact with them. It is absorbed by the blood, which carries it to the pancreas and the liver. When it reaches the pancreas, it acts as a most powerful stimulant to the discharge of accumulated ferments, and to the production of an additional supply. It stimulates the liver to pour forth bile. At present we are in ignorance as to the chemical nature of this hormone. It is not a proteid substance, nor is it a ferment. If scrapings from the mucous membrane of the duodenum be crushed with sand and hydrochloric acid, the mixture boiled, neutralized with carbonate of soda, and filtered, the clear, colourless liquid which results has a powerful effect upon the pancreas, when injected, in even small quantities, into the blood. Apparently, the cells of the duodenal mucous membrane are constantly producing and accumulating a substance which is converted into secretin when acted on by acid. It is not necessary for the acid to stimulate the living cells. If the mucous membrane is ground up with sand and salt-solution, the filtrate is inactive but an active extract is obtained by treating the crushed cells with HCl. It changes some substance which they contain (provisionally termed “prosecretin”) into the efficient hormone. In the lower portion of the small intestine any maltose that remains is converted into diffusible dextrose. A very large amount of water has been poured into the canal in the various digestive juices. This, together with water drunk, is absorbed in the large intestine. At the lower end of the alimentary canal nothing remains but indigestible substances taken with food, chiefly cellulose, and the pigments and other bodies which, as already said, are eliminated in bile.