126 ESSENTIALS OF CHEMICAL PHYSIOLOGY I 



generally found in the concentrated urine of fevers ; and there 

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

 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 



Fig. 47.— Acid sodium urate. Fkj. 48.— Aeid ammonium urate. 



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

 of the urine may be represented by the equation — 



2C5H2Na2N403 + HgO + CO^ = 2CgH3NaN403 + NaaCO;, 



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



urate] acid] urate] carbonate] 



This deposit may be recognised as follows : — 



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



Fia. 49.— Envelope crystals Via. 50.— Cystin crystals, 



of calcium oxalate. 



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. 



3. 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 

 difliculty in hydrochloric acid. 



