egration
and expulsion. This explains why cattle taken from a herd on magnesian
limestone in spring, after the long, dry feeding of winter, usually have
renal calculi, while cattle from the same herd in the fall, after a
summer's run on a succulent pasture, are almost always free from
concretions. The abundance of liquid taken in the green feed and expelled
through the kidneys and the low density or watery nature of the urine have
so opened the texture and destroyed the density of the smaller stones and
gravel that they have all been disintegrated and removed. This, too, is the
main reason why benefit is derived from a prolonged stay at mineral springs
by the human victims of gravel. If they had swallowed the same number of
quarts of pure water at home and distributed it at suitable times each day,
they would have benefited largely without a visit to the springs.

It follows from what has been just said that a succulent diet, including a
large quantity of water (gruels, sloppy mashes, turnips, beets, potatoes,
apples, pumpkins, ensilage, succulent grasses), is an important factor in
the relief of the milder forms of stone and gravel.

_Prevention._--Prevention of calculus especially demands this supply of
water and watery rations on all soils and in all conditions in which there
is a predisposition to the disease. It must also be sought by attempts to
obviate all those conditions mentioned above as causative of the malady.
Sometimes good rain water can be furnished in limestone districts, but
putrid or bad-smelling rain water is to be avoided as probably more
injurious than that from the limestone. Unsuccessful attempts have been
made to dissolve calculi by alkaline salts and mineral acids, respectively,
but their failure as a remedy does not necessarily condemn them as
preventives. One dram of caustic potash or of hydrochloric acid may be
given daily in the drinking water. In diametrically opposite ways these
attack and decompose the less soluble salts and form new ones which are
more soluble and therefore little disposed to precipitate in the solid
form. Both are beneficial as increasing the secretion of urine. In cases in
which the diet has been too highly charged with phosphates (wheat bran,
etc.), these aliments must be restricted and water allowed ad libitum. If
the crystals passed with the urine are the sharp angular (octahedral) ones
of oxalate of lime, then the breathing should be made more active by
exercise,