CHAPTER XI. 

 EXAMINATION OF URINARY CALCULI. 



HEAT a portion of the finely powdered calculus on plati- 

 num-foil; if it burns completely or leaves only a very small 

 quantity of ash, then it consists of uric acid, ammonium 

 urate, cystine, or xanthine. If it does not burn completely 

 it may contain uric acid or urates, calcium phophate, and 

 magnesium phosphate, or ammonium magnesium phosphate 

 and calcium oxalate. The method to be pursued in the 

 analysis is based on this difference. 



I. THE POWDERED CALCULUS BURNS COMPLETELY. 



Digest the powder by warming gently with dilute hydro- 

 chloric acid (1 : 2). 



(a) The Powder Dissolves Completely or Almost Com- 

 pletely. The calculus consists of cystine or xanthine. 



To test for cystine digest a small portion of the powder 

 with ammonia, filter, let the extract evaporate on a watch- 

 glass, and examine the residue under the microscope : cystine 

 forms hexagonal tablets. Cystine calculi are usually small, 

 have a yellow color and a smooth surface. 



To test for xanthine make the so-called xanthine test with 

 nitric acid and sodium hydroxide solution (see chapter on 

 Muscular Tissue, page 29). 



(6) The Powder Does Not Dissolve Completely. Filter and 

 wash the residue. 



128 



