LV.'/A l/.T VALVULI 457 



not coiiimuu ; they are generally rather soft, and often mueh colored 

 by pigments. 



Calcium oxalate calculi are, according to recent observers,'^ the 

 most oonunon urinai-y concretions.'^ Often they show admixtures of 

 urates or uric acid, which latter frc(iuently 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 

 persons excreting excessive quantities of oxalic acid. Normally 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."^ Oxalic acid may possibly be formed from 

 uric acid, and perhaps also from the carbohydrate group of pro- 

 teins,'*^ and it is possible that abnormally large amounts arise from 

 these sources under pathological conditions. During bacterial de- 

 composition of the urine oxalic acid miay be formed from uric acid 

 (Austin).^' 



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 precipitated as NH^MgPO^, 

 the calcium as Ca3(P04)„, and calcium oxalate and ammonium urate 

 are also thrown down, so that the concretions consist of a mixture of 

 these substances, the magnesium 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 "sec- 

 ondary" concretions, and they are formed usually in the bladder as a 

 consequence 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 consisting princi- 

 pally of Ca.,(POJ. or CaHPO^ 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 

 or urinaiy reaction and not of diet.'* As these stones fuse to a black, 



7* Concerning their structure see Fowler, Johns Hopkins Hospital Reports, 1906 

 (13)..';07. 



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



-« See Austin, Boston Med. and Surg. Journal, 1901 (145), 181. Contradicted 

 by Wegrzynowski. Zeit. phvsiol. Cliem.. 1913 (83), 112. 



TT.Tour. Med. Research. 1906 (15), 314. 



78 Under the name "struvit stone," Poninier (Verh. deut. Path. Gesell.. 1905 

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



