462 CALCIFICATION, CONCRETIONS, AND INCRUSTATIONS 



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 prob- 

 ably by gastric fermentation.'^ Oxalic acid may possibly be formed 

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

 proteins,^ and it is possible that abnormally large amounts arise from 

 these sources under pathological conditions. During bacterial de- 

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

 (Austin). 9 



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 NH4MgP04, 

 the calcium as Ca3(P04)2, 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 Ca3(P04)2 or CaHP04 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 urinary reaction and not of diet.^' .4s 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 intliebody 



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



* See Austin, Boston Med. and Surg. Journal, 1901 (145), ISl. Contradicted 

 by Wegrzynowski, Zeit. physiol. Chem., 1913 (83), 112. 

 9 Jour. Med. Research, 1906 (15), 314. 



"> Under the name "struvit stone," Pommer (Vcrh. deut. Path. Gesell., 1905 

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

 phosphate, forming the hard, rhoml)ic crystals known to mineralogists as "struvit." 

 This is an example of a phosphate stone formed independent of ammoniacal decom- 

 position, a rare occurrence. 



•'Osborne (Jour. Amer. Med. Assoc, 1917 (69), 32) has observed numerous 

 cases of formation of phosphate calculi in tlie urinary bladder of rats kept on diets 

 deficient in fat soluble vitamines. The reason for this association of diet and 

 concretions is not known; possibly the dietary deficiency causes lessened resist- 

 ance to urinary infection. 



