568 THE URINE [CH. XXXVII. 



Deposit of Uric Acid. This is a sandy reddish deposit resembling 

 cayenne pepper. It may be recognised by its crystalline form (fig. 

 429, p. 561) and the murexide reaction. The presence of these 

 crystals generally indicates an increased formation of uric acid, and, 

 if excessive, may lead to the formation of stones or calculi in the 

 bladder. 



Deposit of Urates. This is much commoner, and may, if the 

 urine is concentrated, occur in normal urine when it cools. It is 

 generally found in the concentrated urine of fevers; and there 

 appears to be a kind of fermentation, called the acid fermentation, 

 which occurs in the urine after it has been passed, and which leads 

 to the same result. The chief constituent of the deposit is the acid 



FiQ. 433. Crystals of calcium oxalate. FIG. 434. Crystals of cystin. 



sodium urate, the formation of which from the normal sodium urate 

 of the urine may be represented by the equation : 



2C 5 H 2 Na 2 N 4 O 3 + H 2 O + CO 2 = 2C 5 H 3 NaN 4 O 3 + Na 2 CO 3 . 



[Normal sodium [Water.] [Carbonic [Acid sodium urate.] [Sodium 



urate.] acid.] carbonate.] 



This deposit may be recognised as follows : 



(1) It has a pinkish colour ; the pigment called uro-erythrin is one 

 of the pigments of the urine, but; its relationship to the other urinary 

 pigments is not known. 



(2) It dissolves upon warming the urine. 



(3) Microscopically it is usually amorphous, but crystalline forms 

 similar to those depicted in fig. 431 may occur. Crystals of calcium 

 oxalate may be mixed with this deposit (see fig. 433). 



Deposit of Calcium Oxalate. This occurs in envelope crystals 

 (octahedra) or dumb-bells. It is insoluble in ammonia, and in acetic 

 acid. It is soluble with difficulty in hydrochloric acid. 



Deposit of Cystin. Cystin (C 6 H 12 N 2 S 2 4 ) is recognised by its 

 colourless six-sided crystals (fig. 434). These are rare: they occur 



