/ /.'/A I AM (A LCI I.I 455 



])Jiatos. all hciii^- deposited williout iiiHamuiatioii. The iidlaiuiiiatory 

 formations consist cliictlN of ammonio-magnesiuiii |)lins|)liate and 

 aninioiiium nriite, usually deposited on a foreign body or a primary 

 ealeulus. The extensive study of tiie microscopic structure of urin- 

 ary calculi by Shattock,'- shows also that a nucleus of cells or other 

 organic material is, at least in uric acid calculi, extremely rare, the 

 center being almost always a primary crystalline deposit from a 

 supersaturated solution. 



Calculi formed because of changes in the uriiuiry composition in- 

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

 tradistiiu'tiou to those arising from changes in composition brought 

 about b\ infection and ammoniacal decomposition. Because of the 

 injury ])r()duced by a primary calculus, infection frequently results, 

 and then tlie prinuiry calculus may become the nucleus of a secondar^^ 

 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 (metamorphosed 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 

 framewoi"k remains. They are generally classified according to their 

 ])rominent component, as follows: 



Uric=Acid Calculi. — Uric acid is but slightly 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 urinary 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 conci'etions. 



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 imi)ortaiit 



"2 Proc. Roy. Soc. Med., Path. Sec, 1911 (4), 110. 



'2a Concerning soliihilitv of uric acid in urine see Ifaskins. .lour. P.iol. (liem., 

 191(5 (-26). 205. 



'-Arch. Int. Med., 1913 (11). 92; review of literature. Rosenhloom, (.Tour. 

 Amer. ^led. Assoc, 1915 (05), 101) found but two uric acid stones of twenty-six 

 analyzed. 



