CH. XXXVII. ] INORGANIC SALTS 565 



proteids leaves the body as urea and uric acid ; the sulphur of the 

 proteids is oxidised to form sulphuric acid, which passes into the 

 urine in the form of sulphates. The excretion of sulphates, more- 

 over, though it occurs earlier than that of urea, runs parallel with it. 



Chlorides. The chief chloride is that of sodium. The ingestion 

 of sodium chloride is followed by its appearance in the urine, some 

 on the same day, some on the next day. Some is decomposed to form 

 the hydrochloric acid of the gastric juice. The salt, in passing 

 through the body, fulfils the useful office of stimulating metabolism 

 and secretion. 



Sulphates. The sulphates in the urine are principally those of 

 potassium and sodium. They are derived from the metabolism of 

 proteids in the body. Only the smallest trace enters the body with 

 the food. Sulphates have an unpleasant bitter taste (for instance, 

 Epsom salts) : hence we do not take food that contains them. The 

 sulphates vary in amount from 1*5 to 3 grammes daily. 



In addition to these sulphates there is a small quantity, about 

 one-tenth of the total sulphates, that are combined with organic 

 radicles : these are known as ethereal sulphates, and they originate 

 from putrefactive processes occurring in the intestine. The chief 

 of these ethereal sulphates are phenyl sulphate of potassium and 

 indoxyl sulphate of potassium. The latter originates from the indole 

 formed in the intestine, and as it yields indigo when treated with 

 certain reagents it is sometimes called indican. It is very important 

 to remember that the indican of urine is not the same thing as the 

 indican of plants, which is a glucoside. Both yield indigo, but there 

 the resemblance ceases. 



The formation of these sulphates is somewhat important; the 

 aromatic substances liberated by putrefactive processes in the 

 intestine are poisonous, but their conversion into ethereal sulphates 

 renders them harmless. 



The equation representing the formation of potassium phenyl-sulphate is as 

 follows : 



C 6 H 5 OH + S0 2 /g = S 2<^OK 6H5 + H * a 



[Phenol.] [Potassium [Potassium [Water.] 



hydrogen phenyl-sulphate.] 

 sulphate.] 



Indole (C 8 H 7 N) on absorption is converted into indoxyl : 



C.OHrCH 



The equation representing the formation of potassium indoxyl-sulphate is as 

 follows : 



C 8 H 7 NO + SO - S0 2 86 + H 2 0. 



[Indoxyl.] [Potassium [Potassium [Water.] 



hydrogen indoxyl-sulphate.] 



sulphate.] 



