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830 URINE.
Non-Organized Sediments.
Uric Acid. This acid occurs in acid urines as colored crystals which
are identified partly by their form and partly by their property of giving
the murexid test. On warming the urine they are not dissolved. On
the addition of caustic alkali to the sediment the crystals dissolve, and
when a drop of this solution is placed on a microscope-slide and treated
with a drop of hydrochloric acid, small crystals of uric acid are obtained
which can be easily seen under the microscope.
Acid Urates. These occur only in the sediment of acid or neutral
urines. They are amorphous, clay-yellow, brick-red, rose-colored, or
brownish-red. They differ from other sediments in that they dissolve
on warming the urine. They give the murexid test, and small micro-
scopic crystals of uric acid separate on the addition of hydrochloric
acid. Crystalline alkali urates occur very rarely in the urine, and as a
rule only in such as have become neutral but not alkaline, by alkaline
fermentation. The crystals are somewhat similar to those of neutral
calcium phosphate; they are not dissolved by acetic acid, however,
but give a cloudiness therewith due to small crystals of uric acid.
Ammonium urate may indeed occur as a sediment in a neutral urine
which at first was strongly acid and has become neutralized by the alkaline
fermentation, but it is only characteristic of ammoniacal urines. This
sediment consists of yellow or brownish rounded spheres which are often
covered with thorny-shaped prisms and, because of this, are rather
large and resemble the thorn-apple. It reacts to the murexid test. It
is dissolved by alkalies with the development of ammonia, and crystals
of uric acid separate on the addition of hydrochloric acid to this solution.
Calcium oxalate occurs in the sediment generally as small, shining,
strongly refractive quadratic octahedra, which on microscopical examina-
tion remind one of a letter-envelope. The crystals can only be mistaken
for small, not fully developed crystals of ammonium-magnesium phos-
phate. They differ from these by their insolubility in acetic acid. The
oxalate may also occur as flat, oval, or nearly circular disks with central
cavities which from the side appear like an hour-glass. Calcium oxalate
may occur as a sediment in an acid as well as in a neutral or alkaline
urine. The quantity of calcium oxalate separated from the urine as
sediment depends not only upon the amount of this salt present, but
also upon the acidity of the urine. The solvent for the oxalate in the
urine seems to be the diacid alkali phosphate, and the greater the quan-
tity of this salt in the urine the greater the quantity of oxalate in solu-
tion. When, as previously mentioned (page 829), the simple-acid phos-
phate is formed from the diacid phosphate, on allowing the urine to
stand, a corresponded part of the oxalate may be separated as sediment.
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