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41S THE LIVER.
The different bile-acids occur in the bile as alkali salts, generally
the sodium compounds, even in sea-fishes, although this is contrary to
the earlier observations (Zanetti 1
). In the bile of certain animals we
find almost solely glycocholic acid, in others only taurocholic acid, and
in still others a mixture of both (see below).
All alkali salts of .the biliary acids are soluble in water and alcohol,
but insoluble in ether. Their solution in alcohol is therefore precipitated
by ether, and this precipitate, with proper care in manipulation, gives,
for nearly all kinds of bile thus far investigated, rosettes or balls of fine
needles, or four- to six-sided prisms (Plattner’s crystallized bile). Fresh
human bile also crystallizes readily. The bile-acids and their salts
are optically active and dextrorotatory. The salts of the different bile-
acids act somewhat differently toward neutral salts. The alkali salts
of the ordinary and best-studied bile-acids from man, ox, and dog are,
according to Tengstrom,2
precipitated by ammonium and magnesium
sulphates, and also, in pure form, by sodium nitrate and sodium chloride
(added to saturation). Potassium and sodium sulphates do not precip-
itate them. The alkali salts cannot be directly precipitated from the
bile by NaCl, on account of the presence of bodies retarding precipita-
tion, among which we find oil-soaps.
The bile-acids are dissolved by concentrated sulphuric acid at the
ordinary temperature, forming a reddish-yellow liquid which has a beautiful
green fluorescence. According to Pregl an oxidation with a reduction
of the sulphuric acid into sulphur dioxide takes place. The fluorescent
substance has been called dehydrocholan (see below) by Pregl.3
On
carefully warming with concentrated sulphuric acid and a little cane-
sugar, the bile-acids give a beautiful cherry-red or reddish-violet liquid.
Pettenkofer’s reaction for bile-acids is based on this behavior.
Pettenkofer’s test for bile-acids is performed as follows: A small
quantity of bile in substance is dissolved in a small porcelain dish in con-
centrated sulphuric acid and warmed, or some of the liquid contain-
ing the bile-acids is mixed with concentrated sulphuric acid, taking special
care in both cases that the temperature does not rise higher than 60-
70° C. Then a 10-pcr-cent solution of cane-sugar is added, drop by
drop, continually stirring with a glass rod. The presence of bile is indi-
cated by the production of a beautiful red liquid, whose color does not
disappear at the ordinary temperature, but becomes more bluish-violet
in the course of a day. This red liquid shows a spectrum with two absorp-
tion-bands, the one at F and the other between D and E, near E.
iSee Chem. Centralbl., 1903, 1, 180.
2
Zeitschr. f. physiol. Chem., 41.
3
Zeitschr. f. physiol. Chem., 45.
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