ormed
from the venous blood, and taken from the waste and disintegration of
animal tissue, it would appear that it is chiefly an excrementitious
fluid. It does not seem to have accomplished its function when
discharged from the liver and poured into the intestine, for there it
undergoes various alterations previous to re-absorption, produced by its
contact with the intestinal juices. Thus the bile, after being
transformed in the intestines, re-enters the blood under a new form, and
is carried to some other part of the system to perform its mission.

The _Spleen_ is oval, smooth, convex on its external, and irregularly
concave on its internal, surface. It is situated on the left side, in
contact with the diaphragm and stomach. It is of a dark red color,
slightly tinged with blue at its edges. Some physiologists affirm that
no organ receives a greater quantity of blood, according to its size,
than the spleen. The structure of the spleen and that of the mesenteric
glands are similar, although the former is provided with a scanty supply
of lymphatic vessels, and the chyle does not pass through it, as through
the mesenteric glands. The _Pancreas_ lies behind the stomach, and
extends transversely across the spinal column to the right of the
spleen. It is of a pale, pinkish color, and its secretion is analogous
to that of the salivary glands; hence it has been called the _Abdominal
Salivary Gland_.

[Illustration: Fig. 34.
Digestive organs. _3_. The tongue. _7_. Parotid
gland. _8_. Sublingual gland. _5_. Esophagus. _9_.
Stomach. _10_. Liver. _11_. Gall-bladder, _14_. Pancreas.
_13, 13_. The duodenum. The small and large intestines
are represented below the stomach.]

Digestion is effected in those cavities which we have described as parts
of the alimentary canal. The food is first received into the mouth,
where it is masticated by the teeth, and, after being mixed with mucus
and saliva, is reduced to a mere pulp; it is then collected by the
tongue, which, aided by the voluntary muscles of the throat, carries the
food backward into the pharynx, and, by the action of the involuntary
muscles of the pharynx and esophagus, is conveyed to the stomach. Here
the food is subjected to a peculiar, churning movement, by the alternate
relaxation and contraction of the fibers which compose the muscular wall
of the stomach. As soon as the food comes in contact with the stomach,
its pinkish color changes to a bright red; and from the nume