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URIC ACID. G99
oxalic acid, urea, and allantoin, which last is glyoxyldiureide, arc pro-
duced (see below). By oxidation with nitric acid in the cold, urea and
a monoureide, the mesoxalyl urea, or alloxan, are obtained, (’.-,114X403+
+H2O = C’ 4 H2N204+(NH2)2C0. On warming with nitric acid, alloxan
yields carbon dioxide and oxalyl urea, or parabanic acid, C3H2N2O3.
By the addition of water the parabanic acid passes into oxaluric acid,
C3H4N2O4, traces of which are found in the urine and which easily splits
into oxalic acid and urea. In alkaline solution uric acid may, by taking
up water and oxygen, be transformed into a new acid, uroxanic acid,
CsEfeNiOe, which may then be changed into oxonic acid, C4H5N3O4.1
On the oxidation of uric acid by hydrogen peroxide in alkaline solution
Sc iiittenhelm and Wiener 2
have obtained urea with carbonyl diurea
as intermediary product. Uric acid may, as F. and L. Sestini as well
as Gerard have shown, undergo bacterial fermentation with the forma-
tion of urea. According to Ulpiani and Cingolani,3
uric acid is quan-
titatively split into urea and carbon dioxide, according to the equation
C5H^V>:,+2H2 +30 = 3C02 +2CO(NH2)2 .
Uric acid occurs most abundantly in the urine of birds and of scaly
amphibians, in which animals the greater part of the nitrogen of the urine
appears in this form. Uric acid frequently occurs in the urine of carniv-
orous mammalia, but is sometimes absent; in urine of herbivora it is
habitually present, though only as traces; in human urine it occurs in
greater but still small and variable amounts. Traces of uric acid are
also found in several organs and tissues, as in the spleen, lungs, heart,
pancreas, liver (especially in birds), and in the brain. It always occurs
in the blood of birds. Traces have been found in human blood under
normal conditions. Under pathological conditions it occurs to an
increased extent in the blood, as in pneumonia and nephritis, but espe-
cially in leucaemia and sometimes also in arthritis. Uric acid also occurs
in large quantities in " chalk-stones," certain urinary calculi, and in
guano. It has also been detected in the urine of insects and certain
snails, as also in the wings (which it colors white) of certain butterflies
(Hopkins 4
).
The amount of uric acid eliminated with human urine is subject to
considerable individual variation, but amounts on an average to 0.7
1
See Sundwik, Zeitschr. f. physiol. Chem., 20 and 41; also Behrend, Annal. d.
Chem. u. Pharm., 333.
2
Zeitschr. f . physiol. Chem., 62.
3
See Chem. Centralbl., 1903, where the other investigators are cited, and Centralbl.
f. Physiol., 19.
4
Philos. Trans. Roy. Soc, 186, B, 661.
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