In diseases affecting the liver, the urine frequently becomes
contaminated with biliary constituents. If the coloring matter of bile
is present (_bilirubin_, etc.), the liquid is darkened considerably in
tint, and may assume various shades of brown or green. Should the
color be decided, the fluid will be found to foam strongly on shaking,
and white blotting-paper will be stained by it yellow or greenish.
These characters point to the presence of bile in fair quantity, and
it is only necessary to apply a single confirmatory test. Allow some
of the urine to flow carefully, according to Heller's method, over a
couple of drachms of yellow nitric acid (i.e., acid containing traces
of the lower oxides of nitrogen). A number of rapidly changing colors
soon appear, passing through green, blue, violet, and red to yellow.
The first of these tints, green, is the only one that undoubtedly
points to the presence of biliary coloring matter, all the others
being yielded by another constituent of urine, indican, when similarly
treated. Should the color of the urine suggest the presence of only
traces of bile, the best plan is not to treat the urine directly, but
extract a quantity of it by shaking with chloroform. On separating the
latter, and covering with yellowish nitric acid, the color changes
will be observed penetrating into the chloroform. A little, also,
evaporated on a slide yields reddish crystals, which exhibit a pretty
play of colors under the microscope when touched with nitric acid.
It is not unfrequently considered important to test urine for the
sodium salts of the conjugate biliary acids, taurocholic and
glycocholic. Dr. Oliver, of Harrogate, has proposed the use of an
acidulated peptone solution for this purpose, and the reaction is
undoubtedly a good one. The reagent is prepared by dissolving 30
grains of flesh peptone, 4 grains of salicylic acid, and 30 minims of
strong acetic acid, in sufficient water to produce 8 fluid oz. of
solution. Thus prepared, the peptone shows no signs of decomposition
on keeping. To use the test, mix 1 fluid drachm of the reagent with 20
minims of urine, previously diluted to a standard specific gravity of
1.003. A haze is produced, which will be found to be more or less
distinct, according to the proportion of bile salts present.