URINE. 349 



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 melt but yields a bluish-green flame. 



FIG. 103. 



I 



CYSTINE. (Ogden.} 



Cholesterol. Cholesterol crystals have been but rarely detected 

 in urinary sediments. When present they probably arise from a 

 pathological condition of some portion of the urinary tract. Crys- 

 tals of cholesterol have been found in the sediment in cystitis, pye- 

 litis, chyluria and nephritis. Ordinarily it crystallizes in large reg- 

 ular and irregular colorless, transparent plates, some of which pos- 

 sess notched corners (Fig. 42, page 159). Frequently, instead of 

 occurring in the sediment, it is found in the form of a film on the 

 surface of the urine. 



Hippuric Acid. This is one of the rarer sediments of human 

 urine. It deposits under conditions similar to those which govern 

 the formation of uric acid sediments. The crystals, which are 

 colorless needles or prisms (Fig. 92, page 282) when pure, are in- 

 variably pigmented in a manner similar to the uric acid crystals 

 when observed in urinary sediment and because of this fact are fre- 

 quently confounded with the rarer forms of uric acid. Hippuric 

 acid may be differentiated from uric acid from the fact that it does 

 not respond to the murexide test and is much more soluble in water 

 and in ether. The detection of crystals of hippuric acid in the urine 

 has very little clinical significance, since its presence in the sediment 

 depends in most instances very greatly upon the nature of the diet. 

 It is particularly prone to occur in the sediment after the ingestion 

 of certain fruits as well as after the ingestion of benzoic acid (see 

 page 282). 



Leucine and Tyrosine. Leucine and tyrosine have frequently 

 been detected in the urine, either in solution or as a sediment. 

 Neither of them occurs in the urine ordinarily except in association 



