158 



DISEASES OF CATTLE. 



the horsetails (Equisetacece), bamboos, and sedges. The percentage of 

 silica in the ash of several common fodder plants is given below : 



It is only soluble silica that is taken up into the system, and it is in 

 this form (usually as silicate of potash or soda) that it enters the urine, 

 but all that is wanted to precipitate it in crystalline form as a gritty 

 sand is the presence of oxalic or other acid having a stronger affinity 

 for its base (potash or soda). 



Other conditions, however, enter largely into the causation of stone 

 or gravel. A high density of urine resulting from, a highly saturated 

 condition is often present for a length of time without any precipitation 

 of solid materials. Urea and carbonates may be present in excess, 

 the food may be given dry, and drinking water may be deficient in 

 amount without any deposition of stone or gravel. The presence of 

 iioncrystalline organic matter in the urine becomes in such cases an 

 exciting cause. Rainey and Ord have shown experimentally that col- 

 loid (noncrystallizable) bodies like mucus, epithelial cells, albumen, 

 pus, blood, hyaline casts of the kidney tubes, etc., not only determine 

 the precipitation of crystallizable salts from a strong solution, but they 

 determine the precipitation in the form of globular masses or minute 

 spheres, which, by further similar accessions, become stones or calculi 

 of various sizes. The salts that are deposited by mere chemical reac- 

 tion without the intervention of colloids appear in the form of sharply 

 defined angular crystals, and hence the rough, jagged crystals of oxa- 

 late of lime or ammonio-magnesium phosphate. Heat intensifies the 

 action of the colloids in causing precipitation of the dissolved salts, so 

 that the temperature of the kidneys and bladder constitute favorable 

 conditions. Colloids that are undergoing decomposition are also spe- 

 cially powerful, so that the presence of bacteria or fungi causing fer- 

 mentation are important factors. 



In looking, therefore, for the immediate causes of urinary calculi, we 

 must accord a high place to all those conditions which determine the 

 presence of excess of mucus, albumen, pus, blood, kidney casts, blood 

 coloring matter, etc., in the urine. Acatarrhal inflammation of the pel- 

 vis of the kidney, the ureter of the bladder, generating excess of mucus 

 or pus; inflammation of the kidneys causing the discharge into the 

 urinary passages cf blood, albumen or hyaline casts; inflammation of 



