460 CALCIFICATION, CONCRETIONS, AND INCRUSTATIONS 



Calculi formed because of changes in the urinary composition in- 

 dependent of evident infection are often called "primary," in con- 

 tradistinction to those arising from changes in composition brought 

 about by infection and ammoniacal decomposition. Because of the 

 injury produced by a primary calculus, infection frequently results, 

 and then the primary calculus may become the nucleus of a secondary 

 calculus; indeed, on account of the change of reaction, the crystalloids 

 of the primary calculus may be dissolved out, and their place taken by 

 the secondary deposit {metamor'phosed calculi). In structure urin- 

 ary calculi usually show both radiating and concentric lines of forma- 

 tion, and when the chief constituents are dissolved away, an organic 

 framework remains. They are generally classified according to their 

 prominent component, as follows: 



Uric=Acid Calculi. — Uric acid is but shghtly soluble, only one 

 part dissolving in 39,480 of pure water at 18°, and it is even less soluble 

 in the presence of acids.^ The presence of sodium diphosphate in the 

 solution makes it much more soluble, and various organic bodies also 

 favor its solution, among them being the urinarj^ pigments. As can 

 be seen, the maintenance of uric acid in solution is by a small margin, 

 even in normal conditions; hence the mere cooling of the urine fre- 

 quently suffices to cause an abundant deposition of uric acid combined 

 with pigment, as the familiar "brick-dust" deposit. The formation 

 of uric-acid calculi is, therefore, not only a question of the amount of 

 uric acid in the urine, but depends even more upon the amount of the 

 substances that hold it in solution, and as both these factors are sub- 

 ject to wide variations under both physiological and pathological con- 

 ditions, uric acid and urates are common in urinary concretions. 



The older literature indicates that the most common calculus is of 

 this nature, but a number of recent analyses indicate that the im- 

 portance of uric acid and urates has been overestimated. On the con- 

 trary, this material rarely forms a considerable part of the calculi, 

 but is usually present in greater or less amount in most or all urinary 

 calculi (Kahn).^ It is probable, however, that uric acid is important 

 as furnishing the primary nucleus of calculi of preponderatingly cal- 

 careous or mixed composition. Apparently there are marked differ- 

 ences in the prevailing composition of calculi in different countries; in 

 China, for example, Pfister'^ found eleven of twelve calculi composed 

 of uric acid. 



Uric acid is eliminated combined chiefly with sodium, potassium, 

 and ammonium; according to some authors, as abiurate, according to 

 others, as a quadriurate. If the urine is excessively acid, it con- 



^ Concerning solubility of uric acid in urine see Haskins, Jour. Biol. Chem., 

 1916 (26), 205. 



* Arch. Int. Med., '1913 (11), 92; review of literature. Rosenbloom, (Jour. 

 Amer. Med. Assoc, 1915 (65), 161) found but two uric acid stones of twenty-six 

 analyzed. 



6 Zeit. Urol., 1913 (7), 915. 



