ids of the
urine they dispose it to precipitate its least soluble constituents.
Thus the horse is very subject to calculi on certain limestone soils, as
over the calcareous formations of central and western New York,
Pennsylvania, and Ohio, in America; of Norfolk, Suffolk, Derbyshire,
Shropshire, and Gloucestershire, in England; of Poitou and Landes, in
France; and Munich, in Bavaria.

The saturation of the urine from any or all of these conditions can only
be looked on as an auxiliary cause, however, and not as in itself an
efficient one, except on the rarest occasions. For a more direct and
immediate cause we must look to the organic matter which forms a large
proportion of all urinary calculi. This consists of mucus, albumen, pus,
hyaline casts of the uriniferous tubes, epithelial cells, blood, etc.,
mainly agents that belong to the class of colloid or noncrystalline
bodies. A horse may live for months and years with the urine habitually
of a high density and having the mineral constituents in excess without
the formation of stone or gravel; again, one with dilute urine of low
specific gravity will have a calculus.

Rainey, Ord, and others furnish the explanation. They not only show that
a colloid body, like mucus, albumen, pus, or blood, determined the
precipitation or the crystalline salts in the solution, but they
determined the precipitation in the form of globules, or spheres,
capable of developing by further deposits into calculi. Heat intensifies
this action of the colloids, and a colloid in a state of decomposition
is specially active. The presence, therefore, of developing fungi and
bacteria must be looked upon as active factors in causing calculi.

In looking, therefore, for the immediate causes of calculi we must
consider especially all those conditions which determine the presence of
albumen, blood, and excess of mucus, pus, etc., in the urine. Thus
diseases of distant organs leading to albuminuria, diseases of the
kidneys and urinary passages causing the escape of blood or the
formation of mucus or pus, become direct causes of calculi. Foreign
bodies of all kinds in the bladder or kidney have long been known as
determining causes of calculi and as forming the central nucleus. This
is now explained by the fact that these bodies are liable to carry
bacteria into the passages and thus determine decomposition, and they
are further liable to irritate the mucous membrane and become enveloped
in a coating of