mucus, pus, and perhaps blood.

The fact that horses, especially on the magnesian limestones, the same
districts in which they suffer from goiter, appear to suffer from
calculi may be similarly explained. The unknown poison which produces
goiter presumably leads to such changes in the blood and urine as will
furnish the colloid necessary for precipitation of the urinary salts in
the form of calculi.

CLASSIFICATION OF URINARY CALCULI.

These have been named according to the place where they are found, renal
(kidney), ureteric (ureter), vesical (bladder), urethral (urethra), and
preputial (sheath, or prepuce). They have been otherwise named according
to their most abundant chemical constituent, carbonate of lime, oxalate
of lime, and phosphate of lime calculi. The stones formed of carbonates
or phosphates are usually smooth on the surface, though they may be
molded into the shape of the cavity in which they have been formed; thus
those in the pelvis of the kidney may have two or three short branchlike
prolongations, while those in the bladder are round, oval, or slightly
flattened upon each other. Calculi containing oxalate of lime, on the
other hand, have a rough, open, crystalline surface, which has gained
for them the name of mulberry calculi, from a supposed resemblance to
that fruit. These are usually covered with more or less mucus or blood,
produced by the irritation of the mucous membrane by their rough
surfaces. The color of calculi varies from white to yellow and deep
brown, the shades depending mainly on the amount of the coloring matter
of blood, bile, or urine which they may contain.

_Renal calculi._--These may consist of minute, almost microscopic,
deposits in the uriniferous tubes in the substance of the kidney, but
more commonly they are large masses and lodged in the pelvis. The larger
calculi, sometimes weighing 12 to 24 ounces, are molded in the pelvis of
the kidney into a cylindroid mass, with irregular rounded swellings at
intervals. Some have a deep brown, rough, crystalline surface of oxalate
of lime, while others have a smooth, pearly white aspect from carbonate
of lime. A smaller calculus, which has been called coralline, is also
cylindroid, with a number of brown, rough, crystalline oxalate of lime
branches and whitish depressions of carbonate. These vary in size from
15 grains to nearly 2 ounces. Less frequently are found masses of very
hard, brownish white, rounded, pealike calculi. The