the
stomach, intestines, and spleen, and passes it to the liver. This blood is
loaded with food materials, but contains little or no oxygen. The _hepatic
artery_, which branches from the aorta, carries to the liver blood rich in
oxygen. In the liver the portal vein and the hepatic artery divide and
subdivide, and finally empty their blood into a single system of
capillaries surrounding the liver cells. These capillaries in turn empty
into a single system of veins which, uniting to form the _hepatic veins_
(two or three in number), pass the blood into the inferior vena cava (Fig.
72).

[Fig. 72]

Fig. 72--*Relations of the liver.* Diagram showing the connection of the
liver with the large blood vessels and the food canal.

The liver secretes daily from one to two pounds of a liquid called _bile_.
A reservoir for the bile is provided by a small, membranous sack, called
the _gall bladder_, located on the underside of the liver. The bile passes
from the gall bladder, and from the right and left lobes of the liver, by
three separate ducts. These unite to form a common tube which, uniting
with the duct from the pancreas, empties into the duodenum. Though usually
described as a digestive gland, the liver has other functions of equal or
greater importance (Chapter XIII).

*The Bile* is a golden yellow liquid, having a slightly alkaline reaction
and a very bitter taste. It consists, on the average, of about 97 per cent
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 low