far the greater portion of this fluid. The latter are clusters of round
follicles opening into a common excretory duct. These sacs are composed
of delicate, membranous tissue, having numerous nuclei on their walls.
The difficulty of obtaining this juice for experiment is obvious, and
therefore its chemical composition and physical properties are not
known. The intestinal juice resembles the secretion of the mucous
follicles of the mouth, being colorless, vitreous in appearance, and
having an alkaline reaction.

PANCREATIC JUICE. This is a colorless fluid, secreted in a lobular gland
which is situated behind the stomach, and runs transversely from the
spleen across the vertebral column to the duodenum. The most important
constituent of the pancreatic juice is an organic substance, termed
_pancreatin_.

THE BILE. The blood which is collected by the veins of the stomach,
pancreas, spleen, and intestines, is discharged into a large trunk
called the portal vein, which enters the liver. This organ also receives
arterial blood from a vessel called the _hepatic artery_, which is given
off from the aorta below the diaphragm. If the branches of the portal
vein and hepatic artery be traced into the substance of the liver, they
will be found to accompany one another, and to subdivide, becoming
smaller and smaller. Finally, the portal vein and hepatic artery will be
found to terminate in capillaries which permeate the smallest
perceptible subdivisions of the liver substance, which are polygonal
masses of not more than one-tenth of an inch in diameter, called the
_lobules_. Every lobule rests upon one of the ramifications of a great
vessel termed the _hepatic vein_, which empties into the inferior vena
cava. There is also a vessel termed the _hepatic duct_ leading from the
liver, the minute subdivisions of which penetrate every portion of the