conditions, however, the phosphates may contribute to the formation of
calculi, and this, above all, is liable if the urine is retained in the
bladder until it has undergone decomposition and given off ammonia. The
ammonia at once unites with the phosphate of magnesia to form a double
salt--phosphate of ammonia and magnesia--which, being insoluble, is at
once precipitated. The precipitation of this salt is, however, rare in
the urine of the horse, though much more frequent in that of man and
sheep.

These are the chief mineral constituents of the urine which form
ingredients in the horse's calculi, for though iron and manganese are
usually present it is only in minute quantities.

The excess of mineral matter in a specimen of urine unquestionably
contributes to the formation of calculi, just as a solution of such
matters out of the body is increasingly disposed to throw them down in
the form of crystals as it becomes more concentrated and approaches
nearer to the condition of saturation. Hence, in considering the causes
of calculi we can not ignore the factor of an excessive ration, rich in
mineral matters and in carbonaceous matters (the source of carbonates
and much of the oxalates), nor can we overlook the concentration of the
urine that comes from dry feed and privation of water, or from the
existence of fever which causes suspension of the secretion of water. In
these cases, at least the usual quantity of solids is thrown off by the
kidneys, and as the water is diminished there is danger of its
approaching the point of supersaturation, when the dissolved solids must
necessarily be thrown down. Hence, calculi are more common in stable
horses fed on dry grain and hay, in those denied a sufficiency of water
or that have water supplied irregularly, in those subjected to profuse
perspiration (as in summer), and in those suffering from a watery
diarrhea. On the whole, calculi are most commonly found in winter,
because the horses are then on dry feeding, but such dry feeding is even
more conducive to them in summer when the condition is aggravated by the
abundant loss of water by the skin.

In the same way the extreme hardness of the water in certain districts
must be looked upon as contributing to the concentration of the urine
and correspondingly to the production of stone. The carbonates,
sulphates, etc., of lime and magnesia taken in the water must be again
thrown out, and just in proportion as these add to the sol