494 ANIMAL PHYSIOLOGY, 
importance, occurring in small quantities, are bodies that may 
be regarded as less oxidized forms of nitrogenous metabolism, 
such as creatinin, xanthin, hypoxanthin (sarkin), hippuric acid, 
H, 
ammonium oxalurate, and urea, CO ny The latter was 
2 
first prepared artificially from ammonium cyanaie, Ni 0, 
with which it is isomeric. 
When air has free access to urine for some time in a warm 
room, the urea becomes ammonium carbonate by hydration, 
probably owing to the influence of micro-organisms, thus: 
CO (NH), + 2 H.O =.(NH,). CO,; hence the strong ammonical 
smell of old urine, urinals, ete. 
Uric acid (CsH.N,O,) occurs sparingly (see table), combined 
with sodium and ammonium chiefly as acid salts. Since these 
salts are not so soluble in cold as in warm water, they often 
fall as a sediment in the vessel in which the urine stands, and 
present a brick-red or fawn color. 
Uric acid is itself rather insoluble in cold water or hydro- 
chloric acid, though soluble in alkalies; hence it may be 
obtained by adding hydrochloric acid to the urine in the cold. 
When it is in excess it may separate out on standing, forming 
characteristic colored (dark-red) crystals, adhering to the sides 
of the vessel, floating on the top of the urine, or as a sediment 
at the bottom (like red-pepper grains). 
Non-nitrogenous Organic Bodies.—W hether traces of sugar are 
normal in urine is as yet undetermined. Certain acids occur, 
at least frequently, in small quantities, and combined mostly 
with bases. Among these are lactic, formic, oxalic, succinic, 
etc. A series of well-known aromatic bodies occurs in urine, 
especially in that of the horse, cow, etc. These are phenol, 
cresol, pyrocatechin, which occur not free, but united with sul 
phuric acid. 
Inorganic Salts —These are mostly in simple solution, in uring; 
and not, as in some other fluids of the body, united with pro- 
teid bodies. The salts are chlorides, phosphates, sulphates, 
nitrates, and carbonates, the first three being the most abun- 
dant; the bases being sodium, potassium, calcium, magnesium. 
Since the earthy salts can not remain in solution in an alkaline 
fluid, they are usually found as a sediment when the urine loses 
its acid reaction. The phosphates are to be traced to the food, 
to the phosphorus of proteids, and to phosphorized fats (leci- 
thin). The sulphates are derived from those of the food and 
from the sulphur of the proteids of the body. So much of the 
