564 



THE URINE. 



TCH. xxxvu. 



The chemical substances are uric acid, urates, calcium oxalate, 

 calcium carbonate, and phosphates. Rarer forms are leucine, 

 tyrosine, xanthine, and cystin. We shall, however, here only 

 consider the commoner deposits, and for their identification the 

 microscope and chemical tests must both be employed. 



Deposit of Uric Acid. This is a sandy reddish deposit 

 resembling cayenne pepper. It may be recognised by its crystal- 

 line form (tig. 433, p. 556) and the murexide reaction. The 

 presence of these crystals generally indicates an increased forma- 

 tion of uric acid, and, if excessive, may lead to the formation of 

 stones or calciili in the bladder. 



Fig. 437. Crystals of Calcium Oxalate. 



Fig. 438. Crystals of Cystin. 



Deposit of TTrates. 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 



[Normal sodium 

 urate] 



H 2 



[Water] 



C0 2 = 2C 5 H 3 NaN 4 3 



[Carbonic [Acid sodium 



aeid] 



urate] 



[Sodium 

 carbonate]. 



This deposit may be recognised as follows : 



( i ) 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. 435 may occur. 



