oe bend of the
duodenum.

The cystic duct leads back to the under surface of the liver, where
it expands into a sac capable of holding about two ounces of fluid, and is
known as the gall bladder. Thus the bile, prepared in the depths of
the liver by the liver cells, is carried away by the bile ducts, and may
pass directly into the intestines to mix with the food. If, however,
digestion is not going on, the mouth of the bile duct is closed, and in
that case the bile is carried by the cystic duct to the gall bladder. Here
it remains until such time as it is needed.

149. Blood Supply of the Liver. We must not forget that the liver
itself, being a large and important organ, requires constant nourishment
for the work assigned to it. The blood which is brought to it by the
portal vein, being venous, is not fit to nourish it. The work is done by
the arterial blood brought to it by a great branch direct from the aorta,
known as the hepatic artery, minute branches of which in the form of
capillaries, spread themselves around the hepatic lobules.

The blood, having done its work and now laden with impurities, is picked
up by minute veinlets, which unite again and again till they at last form
one great trunk called the hepatic vein. This carries the impure
blood from the liver, and finally empties it into one of the large veins
of the body.

After the blood has been robbed of its bile-making materials, it is
collected by the veinlets that surround the lobules, and finds its way
with other venous blood into the hepatic vein. In brief, blood is brought
to the liver and distributed through its substance by two distinct
channels,--the portal vein and the hepatic artery, but it leaves
the liver by one distinct channel,--the hepatic vein.

[Illustration: Fig. 59--Showing the Relations of the Duodenum and Other
Intestinal Organs. (A portion of the stomach has been cut away.)]

150. Functions of the Liver. We have thus far studied the liver only
as an organ of secretion, whose work is to elaborate bile for future use
in the process of digestion. This is, however, only one of its functions,
and perhaps not the most important. In fact, the functions of the liver
are not single, but several. The bile is not wholly a digestive fluid, but
it contains, also, materials which are separated from the blood to be
cast out of the body before they work mischief. Thus, the liver ranks
above all others as an organ of excretion, that is, it separa