220 



Retrogressive Processes. 



separates from a saturated solution of copper sulphate or from 

 Carlsbad-Sprudel water, in the same manner the salts of a secre- 

 tion, like the urine, may precipitate, especially should there occur 

 a loss of its fluid or of substances which keep the salts in solution. 



2. Retention of secretions or excretions in their storage reser- 

 voirs. 



3. Chemical decomposition of the secretion, with the formation 

 of insoluble products, as may result from the presence of bacteria 

 ( ammoniacal fermentation ) . 



4. Presence of a foreign body or any organic material which 

 serves as a nucleus for the deposition of crystals, or as a supporting 



framework for the precipi- 

 tated salts, as bits of wood, 

 particles of food, or viscid 

 degenerative products. 



Urinary Calculi {Uro- 

 lithiasis s^ravel, concrc- 

 nicnta urinaria). — The sa- 

 line constituents of the 

 urine may be precipitated 

 in the kidneys, in the renal 

 pelvis and in the urinary 

 bladder and give rise to the 

 formation of urinary gravel, 

 urinary sand, and larger 

 urinary calculi. Even nor- 

 mally in the horse, calcium 

 carbonate separates in the 

 pelves of the kidneys and 

 in the bladder from the al- 

 kaline urine, the latter being turbid even when freshly passed in 

 consequence ; in the other herbivora it becomes cloudy soon after it 

 is voided because of loss of the solvent power of its fluid on cool- 

 ing. The acid urine of carnivora and omnivora is, on the contrary, 

 clear and permits sedimentation only after decomposition and long 

 standing. The causes of urinary calculus formation may include 

 such structural elements as parasites, blood clots and coagulated 

 fibrin, shreds of necrotic tissue, tube casts and epithelial cells, these 

 substances afifording a place of attachment for deposition of the 

 inorganic substances. The presence of living or dead bacteria is 

 especially apt to cause precipitation, these at times forming small 



Fig. 34. 



T'rinnr.v falciilus from renal pelvis of 

 horse. 



