URINARY CONCRETIONS 461 



tains much acid j^hospliates, wliicli withdraw part of the bases from 

 the uric acid, and this, when free, crystalhzcs out if in excess. Hence 

 the formation of uric-acid concretions is favored by high acidity of 

 the urine, by concentration of the urine, or by an increased ehmina- 

 tion of the uric acid. The last may result from excessive nuclein- 

 rich food, or from excessive catabolism of the tissue nucleoproteins 

 (e. g., leucocytosis from inflammatory diseases or leukemia), which 

 conditions are also usually associated with an increased urinary acid- 

 ity. The chemistry of uric acid is discussed more fully in the chap- 

 ter on Gout, Chap, xxiii.) 



Uric-acid calculi are formed chiefly in the pelvis of the kidney, but 

 many pass into the bladder. They are quite hard, and yellow or 

 reddish-yellow in color, because of the presence of urochrome and 

 urobilin, the former of which seems to be chemically combined and 

 the latter but physically, since it can be washed out with water. 

 Uroerythrin or uromelanin (a decomposition product of urochrome) 

 may also be present. Not infrequently calcium oxalate is present, 

 .sometimes in considerable quantities. Other urinary constituents may 

 be present in small amounts. In case the calculus enters the urinary 

 bladder it may set up irritation leading to infection; the urine then 

 becoming alkaline, calcium and ammonio-magnesium phosphate will 

 be deposited upon the surface, and the uric acid will be more or 

 less dissolved out and replaced by the phosphates (metamorphosis). 



Urate calculi occur chiefly in new-born or young infants, and 

 rarely in adults. In the young they are related to, and may originate 

 in, the deposits of urates in the pyramids of the kidney (the so-called 

 urate or uric-acid "infarcts"), which have been supposed to result 

 from the decomposition of the nucleoproteins of the nucleated fetal 

 red corpuscles. (See Uric Acid, Chap, xxiii.) The concretions are 

 composed chiefly of either ammonium or sodium urate, but potassium 

 and even calcium and magnesium urate may be admixed. Their 

 genesis in the young probably depends upon injury to epithelium by 

 the excessive urates of the "infarcts," which affords a suitable nucleus 

 for their start; their growth depends chiefly upon the concentration of 

 the infant's urine. In adults they may arise secondary to an am- 

 moniacal decomposition of the urine. Urate concretions are not com- 

 mon; they are generally rather soft, and often much colored b}' 

 pigments. 



Calcium oxalate calculi are, according to recent observers,* the 

 most common urinary concretions.^ Often they show admixtures of 

 urates or uric acid, which latter frequently constitutes the nucleus, and 

 when urinary infection occurs they may in turn serve as the nucleus 

 to phosphatic deposits. On account of the hardness and roughness of 

 tliese stones they frequently cause bleeding, which may result in their 



^ Concerning their structure see Fowler, Johns Hopkins Hospital Reports, 1908 

 (13), 507. 



