Much about the composition of the bile is not understood. It is known, however, to be necessary to digestion, its chief use being to aid in the digestion and absorption of fats. It is claimed also that the bile aids the digestive processes in some general ways—counteracting the acid of the gastric juice, preventing the decomposition of food in the intestines, and stimulating muscular action in the intestinal walls. No enzymes have been discovered in the bile. *The Pancreas* is a tapering and somewhat wedge-shaped gland, and is so situated that its larger extremity, or head, is encircled by the duodenum. From here the more slender portion extends across the abdominal cavity nearly parallel to and behind the lower part of the stomach. It has a length of six or eight inches and weighs from two to three and one half ounces. Its secretion, the pancreatic juice, is emptied into the duodenum by a duct which, as a rule, unites with the duct from the liver. *The Pancreatic Juice* is a colorless and rather viscid liquid, having an alkaline reaction. It consists of about 97.6 per cent of water and 2.4 per cent of solids. The solids include mineral salts (the chief of which is sodium carbonate) and four different chemical agents, or enzymes,—trypsin, amylopsin, steapsin, and a milk-curding enzyme. These active constituents make of the pancreatic juice the most important of the digestive fluids. It acts with vigor on all of the nutrients insoluble in water, producing the following changes: 1. It converts the starch into maltose, completing the work begun by the saliva. This action is due to the _amylopsin_,(61) which is similar to ptyalin but is more vigorous. 2. It changes proteids into peptones and proteoses, completing the work begun by the gastric juice. This is accomplished by the _trypsin_, which is similar to, but more active than, the pepsin. 3. It digests fat. In this work the active agent is the _steapsin_. The necessity of a milk-curding enzyme, somewhat similar to the rennin of the gastric juice, is not understood. *Digestion of Fat.*—Several theories have been proposed at different times regarding the digestion and absorption of fat. Among these, what is known as the "solution theory" seems to have the greatest amount of evidence in its favor. According to this theory, the fat, under the influence of the steapsin, absorbs water and splits into two substances, recognized as glycerine and fatty acid. This finishes the process so far as the glycerine is concerned, as this is soluble in water; but the fatty acid, which (from certain fats) is insoluble in water,(62) requires further treatment. The fatty acid is now supposed to be acted on in one, or both, of the following ways: 1. To be dissolved as fatty acid by the action of the bile (since bile is capable of dissolving it under certain conditions). 2. To be converted by the sodium carbonate into a form of soap which is soluble in water.