80 



even more conducive to them in summer when the condition is aggra- 

 vated 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 carbonates, 

 sulphates, etc., of lime and magnesia taken in the water must be again 

 thrown out, and just in j)roportion as these add to the solids of the 

 urine they dispose it to precipitate its least soluble constituents. Thus 

 the horse is very obnoxious to calculi on certain limestone soils, as over 

 the calcareous formations of central and western New York, Pennsyl- 

 vania, and Ohio, in America; of Norfolk, Suffolk, Derbyshire, Shrop- 

 shire, and Gloucestershire, in England ; of Poitou and Landes, in 

 France ; and Munich, in Bavaria. 



But the saturation of the urine from any or all of these conditions 

 can only be looked on as an auxiliary cause, and not as in itself an 

 efQcient 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 uriuiferous tubes, epithelial cells, 

 blood, etc., mainly agents that belong to the class of colloid or non- 

 crystalline 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; and again one with 

 dilute urine of low specific gravity will have a calculus. 



Eainey, Ord, and others furnish the explanation. They not only 

 show that a colloid body, like mucus, albumen, pus, or blood, deter- 

 mined the ijrecipitation of the crystalline salts in the solution, but they 

 determined the precipitation in the form of globules or spheres, capa- 

 ble 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 kid- 

 neys and urinary passages causing the escape of blood or tlie 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 ex- 

 I>lained 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 coat- 

 ing M mucus, pus, and perhaps blood. 



The fact that horses appear to suffer from calculi, especially on the 

 maguesiau limestones, the same districts in which they suffer from 



