URINE 163 



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

 bladder. 



Deposit of "Orates. 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 

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

 of the urine may be represented by the equation 



20 5 H 2 Na 4 N 4 3 + H a O + CO 2 =2C 5 H 3 NaN 4 O 3 + Na 2 CO 3 



[normal sodium [water] [carbonic [acid sodium [sodium 



urate] acid] nrate] carbonate] 



This deposit may be recognised as follows : 



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



FIG. 47. Acid sodium urate. FtG. 48. Acid ammonium urate. 



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

 pigments is not known (see further Lesson XXVI.). 



2. It dissolves upon warming the urine. 



Microscopically it is usually amorphous, but crystalline forms 

 similar to those depicted in figs. 47 and 48 may occur. 



Crystals of calcium oxalate may be mixed with this deposit (see 

 fig. 49). 



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 O4) is recognised by its 

 colourless six-sided crystals (fig. 50). These are rare : they occur 

 only in acid urine, and they may form concretions or calculi. Cystin- 

 uria (cystin in the urine) is hereditary. 



Deposit of Phosphates. These occur in alkaline urine. The 



M2 



