frequent painful erections. It must be remedied by mechanical
dilatation, with catheters just large enough to pass with gentle force,
to be inserted once a day, and to be used of larger size as the passage
will admit them. The catheter should be kept perfectly clean and washed
in a borax solution and well oiled before it is introduced.

URINARY CALCULI (STONE, OR GRAVEL).

These consist in some of the solids of the urine that have been
precipitated from the urine in the form of crystals, which remain apart
as a fine, powdery mass, or magma, or aggregate into calculi, or stones,
of varying size. (See Pl. XI.) Their composition is therefore determined
in different animals by the salts or other constituents found dissolved
in the healthy urine, and by the additional constituents which may be
thrown off in solution in the urine in disease. In this connection it is
important to observe the following analysis of the horse's urine in
health:

Water 918.5
Urea 13.4
Uric acid and urates .1
Hippuric acid 26.4
Lactic acid and lactates 1.2
Mucus and organic matter 22.0
Sulphates (alkaline) 1.2
Phosphates (lime and soda) .2
Chlorids (sodium) 1.0
Carbonates (potash, magnesia, lime) 16.0
-----
1000.0

The carbonate of lime, which is present in large quantity in the urine
of horses fed on green fodder, is practically insoluble, and therefore
forms in the passages after secretion, and its microscopic rounded
crystals give the urine of such horses a milky whiteness. It is this
material which constitutes the soft, white, pultaceous mass that
sometimes fills the bladder to repletion and requires to be washed out.
In hay-fed horses carbonates are still abundant, while in those mainly
grain-fed they are replaced by hippurates and phosphates--the products
of the wear of tissues--the carbonates being the result of oxidation of
the vegetable acids in the feed. Carbonate of lime, therefore, is a very
common constituent of urinary calculi in herbivora, and in many cases is
the most abundant constituent.

Oxalate of lime, like carbonate of lime, is der