of water and 3 per cent of solids.(60) The solids include bile pigments,
bile salts, a substance called cholesterine, and mineral salts. The
pigments (coloring matter) of the bile are derived from the hemoglobin of
broken-down red corpuscles (page 27).

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: