462 



PHYSIOLOGICAL CHEMISTRY 



137. Ammonium urate is ordinarily present in the sediment in the 

 burr-like form of the " thorn-apple " crystal, i.e., yellow or reddish- 

 brown spheres, covered with sharp spicules or prisms (Plate VI, 

 opposite). The urates are all soluble in hydrochloric acid or acetic 

 acid and their acid solutions yield crystals of uric acid upon standing. 

 They also respond to the murexide test. The clinical significance of 



FIG. 137. Acm SODIUM URATE. 



urate sediments is very similar to that of uric acid. A considerable 

 sediment of amorphous urates does not necessarily indicate a high uric 

 acid content, but ordinarily signifies a concentrated urine having a very 

 strong acidity. 



Cystine. Cystine is one of the rarer of the crystalline urinary sedi- 

 mehts. It has been claimed that it occurs more often in the urine of 



FIG. 138. CYSTINE. (Ogden.) 



men than of women. Cystine crystallizes in the form of thin, color- 

 less, hexagonal plates (Fig. 26, page 76, and Fig. 138) which are 

 insoluble in water, alcohol, and acetic acid, and soluble in minerals, 

 acids, alkalis, and especially in ammonia. Cystine may be identified 

 by burning it upon platinum foil, under which condition it does not 



