116 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



the body, fulfils the useful office of stimulating metabolism and 

 excretion. 



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 v^e 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 of 

 sulphuric acid comprising about one-tenth of the total which 

 is combined with organic radicles ; the compounds are known as 

 ethereal sulphates, and they originate from putrefactive processes 

 occurring in the intestine. The most important 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. Both yield indigo, but there the resemblance ceases. 



The equation representing the formation of potassium phenyl- 

 sulphate is as follows : — 



[phenol] [potassium [potassium [water] 



hydrogen sulphate] phenyl-sulphate] 



The formation of potassium indoxyl-sulphate may be represented 



/-ITT pTX 



as follows : — Indole, C6H4<'^tt" , on absorption is converted 



into indoxyl: C6H4<^g^-G^ 



Indoxyl then interacts with potassium hydrogen sulphate as 

 follows : — 



[indoxyl] [potassium [potassium • 



hydrogen sulphate] indoxyl-sulphate] [water] 



The formation of such sulphates is important ; the aromatic sub- 

 stances liberated by putrefactive processes in the intestine are 

 poisonous, but their conversion into'ethereal sulphates renders them 

 innocuous. 



Carbonates. — Carbonates and bicarbonates of sodium, calcium^ 

 magnesium, and ammonium are only present in alkaline urine. They 

 arise from the carbonates of the food, or from vegetable acids (malic, 



