URINARY CALCULI 383 



persons excreting excessive quantities of oxalic acid. Nor- 

 mally but about 0.02-0.05 gram of oxalic acid is eliminated 

 daily in the urine, apparently all as calcium oxalate, which is 

 kept in solution by the acid phosphates. The amount may be 

 increased by certain foods rich in oxalates, particularly rhubarb, 

 grapes, spinach, etc. ; also probably by gastric fermentation. 1 

 Oxalic acid seems normally to be formed from uric acid, and 

 perhaps also from the carbohydrate group of proteids, 2 and it 

 is possible that abnormally large amounts arise from these 

 sources under pathological conditions. 



Phosphate calculi are formed as a result of decomposition 

 of the urine, with formation of ammonia from the urea. In 

 the ammoniacal solution thus formed the magnesium is precipi- 

 tated as NH 4 MgPO 4 , the calcium as Ca 3 (PO 4 ) 2 , and calcium 

 oxalate and ammonium urate are also thrown down, so that the 

 concretions consist of a mixture of these substances, the mag- 

 nesium salt being the most abundant. In none does one substance 

 occur in a pure state. Pigments of various kinds, and more or 

 less mucus or other organic constituents of the framework are 

 also present. Phosphate calculi are the typical " secondary " 

 concretions, and they are formed usually in the bladder as a con- 

 sequence of cystitis, but may be formed in the renal pelvis or 

 in the urethra. In some cases the salts are precipitated in such 

 large quantities that they form great masses of a sediment which 

 does not aggregate into concretions. Occasionally stones con- 

 sisting principally of Ca 3 (PO 4 ) 2 or CaHPO 4 are formed, but 

 these are rarities. As the calcium taken in the food is chiefly 

 eliminated in the feces, the amount in the urine does not vary 

 directly with the amount in the food, and the formation of 

 phosphatic concretions is always a matter of urinary reaction 

 and not of diet. 3 As these stones fuse to a black, enamel- 

 like mass under the blow-pipe, they have been called " fusible 

 calculi." 



Calcium carbonate calculi are formed frequently in 

 herbivora, but they are very rare in the urinary passages of 

 man, although occurring elsewhere in the body not infrequently. 

 Occasionally these are soft and chalky, but if well crystallized, 

 they are the hardest of concretions. 



1 Baldwin, Jour. Exp. Med., 1900 (5), 27. 



2 See Austin, Boston Med. and Surg. Journal, 1901 (145), 181. 



3 Under the name " struyit stone," Pommer (Verb. deut. Path. Gesell., 

 1905 (9), 28) describes a urinary calculus composed of very pure ammonio- 

 magnesium phosphate, forming the hard, rhombic crystals known to mineralo- 

 gists as " struvit." This is an example of a phosphate stone formed inde- 

 pendent of ammoniacal decomposition, a rare occurrence. 



