480 PHYSIOLOGICAL CHEMISTRY 



melt but yields a bluish-green flame. For preparation of Cystine see 

 Chapter IV. 



Cholesterol. Cholesterol crystals have been but rarely detected in 

 urinary sediments. When present they probably arise from a patho- 

 logical condition of some portion of the urinary tract. Crystals of 

 cholesterol have been found in the sediment in cystitis, pyelitis, 

 chyluria, and nephritis. Ordinarily it crystallizes in large regular and 

 irregular colorless, transparent plates, some of which possess notched 

 corners (Fig. 63, page 213). 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 rare 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. 130, page 406) 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 frequently confounded with the 

 rarer forms of uric acid. Hippuric acid 

 may be differentiated from uric acid 



FIG. 145. CRYSTALS OF IMPURE from the fact that it does not respond to 

 LEUCINE. (Ogden.) . . , , . 



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 pres- 

 ence in the sediment depends in most instances very greatly upon 

 the nature of the diet. It is particularly prone to occur in the sedi- 

 ment after the ingestion of certain fruits as well as after the ingestion of 

 benzoic acid (see pages 405 and 619). 



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 with the 

 others, i.e., whenever leucine is detected it is more than probable that 

 tyrosine accompanies it. They have been found pathologically in 

 the urine in acute yellow atrophy of the liver, in acute phosphorus 

 poisoning, in cirrhosis of the liver, in severe cases of typhoid fever 

 and small-pox, and in leukemia. In urinary sediments leucine ordi- 

 narily crystallizes in characteristic spherical masses which show both 

 radial and concentric stria tions and are highly refractive (Fig. 145). 

 Some investigators claim that these crystals which are ordinarily called 

 leucine are, in reality, generally urates. This view point has become 

 more general in recent years. For the crystalline form of pure leucine 



