DISEASES OP THE URlNARV ORGANS. 213 



are therefore among the causes which strongly predispose to 

 tuinary calculi 



Beside these a certain amount of mucuSy fat, colouring matter^ 

 and even blood enter into the formation of urinary calculi. 



Accessory Causes. — To the above-named causes favouring the 

 formation ot urinary calculi, may be added all such as favour 

 concentration of the urine. Thus scarcity of drinking water, 

 excessive loss of liquid by the bowels or skin (diarrhoea, dysen- 

 tery, etc.), dry winter-feeding on hay and grain, feverish states 

 in which little urine is secreted, and hard waters appear to have 

 this effect The last-named cause is not generally credited by 

 physicians, but its coincidence with the prevalence of stone is 

 exceedingly common. 



Mode of Forf/iation. — The first requisite is that some solid 

 body should exist as a nucleus around which layer after layer is 

 crystallized, and hence the stone is always composed of a series 

 of concentric layers. The nucleus may consist in a particle of 

 mucus, fibrine, or blood, a crystal deposited from over-saturated 

 urine, or even a foreign body introduced from without. I have 

 seen a large calculus in the kidney of a deer formed around a 

 piece of wood which must have penetrated the kidney and 

 broken off, while the wound by which it entered had healed up. 



Appearance. — Calculi vary much in character, but the most 

 marked varieties are the smooth stones formed by carbonates, 

 oxalates, phosphates, and silica, and the rough jagged crystalline 

 specimens of ammonia-magnesian phosphates. 



Re7ial Calculi. — Those found in the kidney are usually 

 moulded in the pelvis, though I have found many like small 

 lentils in dilatations of the microscopic tubes in the substance 

 of the gland. Cattle fed on dry hay and grain, during winter, 

 rarely want small yellow crystalline masses in the pelvis. Even 

 when so large as to distend the pelvis and weigh several ounces, 

 they are not always incompatible with good health and aptitude 

 to fatten. When so large or rough as to produce manifest 



