156 DISEASES OF THE HORSE. 
The excess of mineral matter in a specimen of urine unquestion- 
ably 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 ap- 
proaches nearer to the condition of saturation. Hence, in consider- 
ing 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 priva- 
tion 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 dimin- 
ished there is danger of its approaching the point of supersatura- 
tion, 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 dis- 
tricts must be looked upon as contributing to the concentration of the 
urine and correspondingly to the production of stone. The carbon- 
ates, sulphates, etc., of lime and magnesia taken in the water must be 
again thrown out, and just in proportion as these add to the solids 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, albu- 
men, 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 habit- 
ually 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. 
