EXAMINATION OF NORMAL AND ABNORMAL URINE, 479 



residue indicates calcium oxalate, which can be verified by igniting 

 some of the calculus and adding a drop of acid, when effervescence 

 will be noticed, the oxalate having been converted into a carbonate 

 by the ignition ; the solution thus obtained can be tested for calcium 

 by the addition of water of ammonia and ammonium oxalate. In 

 case phosphoric acid has been found, this is present either as a cal- 

 cium or magnesium-ammonium salt. To distinguish between them, 

 neutralize the solution of the powder in hydrochloric acid with 

 ammonia, add acetic acid and ammonium oxalate ; a white precipi- 

 tate indicates calcium ; if no precipitate is produced, supersaturate 

 with ammonia, when the crystalline magnesium-ammonium phos- 

 phate will gradually form. 



Most common are calculi of uric acid ; often met with are those of 

 urates, phosphates, and oxalates ; rarely, however, those of xanthin 

 and cyst in. 



Microscopical examination of urinary sediments. The chemi- 

 cal examination of any urinary sediment should always be preceded 

 by a microscopical examination, which latter is in many cases the 

 only way of determining the nature of the sediment, especially of the 

 organized substances. 



Fig. 44, A-O, shows the principal sediments found in, or produced 

 from, urine, as seen with a magnifying power of 200 diameters. 



A. Uric add occurs in many different forms, mostly in rhombic 

 plates, with rounded obtuse angles, often joined into rosettes. Uric 

 acid is found almost invariably colored red or reddish-brown, which 

 generally distinguishes it from other sediments. The crystals or 

 clusters of crystals are often large enough to be seen by the naked 

 eye, and are then known by the terms "sand," "gravel," or "red- 

 pepper grains." 



B. Ammonium add urate is found, generally associated with amor- 

 phous or crystalline phosphates, in urine which has become alkaline. 

 The crystalline globules are generally covered with spinous excres- 

 cences, which give them the characteristic "thorn-apple" appearance. 



C. Sodium urate forms generally a part in the pulverulent, heavy, 

 variously tinted deposit of the mixed urates known as "brickdust"or 

 " lateritious " sediment. It occurs either in fine amorphous granules 

 which cannot be distinguished microscopically from other amorphous 

 sediments or in a crystalline form as shown in the figure. 



D. Urea nitrate crystallizes readily in large six-sided plates on the 

 addition of nitric acid to urine. 



