While there
are exceptions, they are so rare that they do not invalidate this general
rule. It is true that stone in the kidney or bladder is often found in the
summer or in animals feeding at the time on a more or less succulent
ration, yet such masses usually date back to a former period when the
animals were restricted to a dry ration.

In this connection is should be noted that a great drain of water from the
system by any other channel than the kidneys predisposes to the production
of gravel or stone. In case of profuse diarrhea, for example, or of
excessive secretion of milk, there is a corresponding diminution of the
water of the blood, and as the whole quantity of the blood is thus
decreased and as the urine secreted is largely influenced by the fullness
of the blood vessels and the pressure exerted upon their walls from within,
it follows that with this decrease of the mass of the blood and the
lessening of its pressure outward there will be a corresponding decrease of
urine. The waste of the tissues, however, goes on as before, and if the
waste matter is passed out through the kidneys it must be in a more
concentrated solution, and the more concentrated the urine the greater the
danger that the solids will be deposited as small crystals or calculi.

Again, the concentrated condition of the urine which predisposes to such
deposits is favored by the quantity of lime salts that may be present in
the water drunk by the animal. Water that contains 20 or 30 grains of
carbonate or sulphate of lime to the gallon must contribute a large
addition of solids to the blood and urine as compared with soft waters from
which lime is absent. In this connection it is a remarkable fact that stone
and gravel in the domesticated herbivora are notoriously prevalent on many
limestone soils, as on the limestone formations of central and western New
York, Pennsylvania, Ohio, and Michigan; on the calcareous formations of
Norfolk, Suffolk, Derbyshire, Shropshire, and Gloucestershire, in England;
in Landes in France, and around Munich in Bavaria. It does not follow that
the abundance of lime in the water and fodder is the main cause of the
calculi, as other poisons which are operative in the same districts in
causing goiter in both man and animal probably contribute to the trouble,
yet the excess of earthy salts in the drinking water can hardly fail to add
to the saturation of both blood and urine, and thereby to favor the
precipitation o