URINE. 



347 



whetstones, prismatic rosettes, irregular rectangular or hexagonal 

 plates, etc. Crystals of pure uric acid are always colorless (Fig. 

 89, page 274), but the form occurring in urinary sediments is im- 

 pure and under the microscope appears pigmented, the depth of 

 color varying from light yellow to a dark reddish-brown according 

 to the size and form of the crystal. 



The presence of a considerable uric acid sediment does not, of 

 necessity, indicate a pathological condition or a urine of increased 

 uric acid content, since this substance very often occurs as a sedi- 

 ment in urines whose uric acid content is diminished from the nor- 

 mal merely as a result of changes in reaction, etc. Pathologically, 

 uric acid sediments occur in gout, acute febrile conditions, chronic 

 interstitial nephritis, etc. If the microscopical examination is not 

 conclusive, uric acid may be differentiated from other crystalline 



FIG. 101. 



VARIOUS FORMS OF URIC ACID. 



i, Rhombic plates; 2, whetstone forms; 3, 3, quadrate forms; 4, 5, prolonged into 

 points ; 6, 8, rosettes ; 7, pointed bundles ; 9, barrel forms precipitated by adding 

 hydrochloric acid to urine. 



urinary sediments from the fact that it is soluble in alkalis, alkali 

 carbonates, boiling glycerol, concentrated sulphuric acid and in cer- 

 tain organic bases such as ethylamine and piperidin. It also re- 

 sponds to the murexide test (see page 274), SchifFs reaction (see 

 page 275) and to Moreigne's reaction (see p. 275). 



Urates. The urate sediment may consist of a mixture of the 



