every portion of the
substance of that organ. Connected with the hepatic duct, is the duct of
a large oval sac, called the _gall-bladder_.

Each lobule of the liver is composed of minute cellular bodies known as
the _hepatic cells_. It is supposed that in these cells the blood is
deprived of certain materials which are converted into bile. This
secretion is a glutinous fluid, varying in color from a dark golden
brown to a bright yellow, has a specific gravity ranging from 1018 to
1036, and a slightly alkaline reaction. When agitated, it has a frothy
appearance. Physiologists have experienced much difficulty in studying
the character of this secretion from the instability of its constituents
when subjected to chemical examination.

[Illustration: Fig. 52.
Section of the Liver, showing the
ramifications of the portal vein. 1. Twig
of portal vein. 2, 2', 2", 2"'. Interlobular
vein. 3, 3', 3", Lobules.]

_Biliverdin_ is an organic substance peculiar to the bile, which imparts
to that secretion its color. When this constituent is re-absorbed by the
blood and circulates through the tissues, the skin assumes a bright
yellow hue, causing what is known as the jaundice. _Cholesterin_ is an
inflammable crystallizable substance soluble in alcohol or ether. It is
found in the spleen and all the nervous tissues. It is highly probable
that it exists in the blood, in some state or combination, and assumes a
crystalline form only when acted upon by other substances or elements.
Two other constituents, more important than either of the above, are
collectively termed _biliary salts_. These elements were discovered in
1848, by Strecker, who termed them _glycocholate_ and _taurocholate of
soda_. Both are crystalline, resinous substances, and, although
resembling each other in many respects, the chemist may distinguish them
by their reaction, for both yield a precipitate if treated with
subacetate of lead, but only the glycocholate will give a precipitate
with acetate of lead. In testing for biliary substances, the most
satisfactory method is the one proposed by Pettenkoffer. A solution of
cane-sugar, one part of sugar to four parts of water, is mixed with the
suspected substance. Dilute sulphuric acid is then added until a white
precipitate falls, which is re-dissolved in an excess of the acid. On
the addition of more sulphuric acid, it becomes opalescent, and passes
through the successive hues of scarlet, lake, and a rich purple. Caref