382 CALCIFICATION, CONCRETIONS, AND INCRUSTATIONS 



usually associated with an increased urinary acidity. (The 

 chemistry of uric acid is discussed more fully in the chapter on 

 " Gout," Chap, xxi.) 



Uric-acid calculi are formed chiefly in the pelvis of the kid- 

 ney, 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. Urcerythrin or uromelanin (a de- 

 composition product of urochrome) may also be present. Not 

 infrequently calcium oxalate is present, sometimes in consider- 

 able 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 nucleo- 

 proteids of the nucleated fetal red corpuscles. (See " Uric Acid," 

 Chap, xxi.) 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 ex- 

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

 for their start ; their growth depends chiefly upon the concen- 

 tration of the infant's urine. In adults they may arise second- 

 ary to an ammoniacal decomposition of the urine. Urate 

 concretions are not common ; they are generally rather soft, 

 and often much colored by pigments. 



Calcium oxalate calculi are the hardest of all concretions 

 (except some forms of the rare calcium carbonate calculi) and 

 in frequency stand next to the uric-acid calculi. 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 these stones they 

 frequently cause bleeding, which may result in their being very 

 dark in color and containing blood-pigment. They are usually 

 first formed in the pelvis of the kidney, and arise chiefly in 



