URINE 563 



From these results he draws the conclusion that urea is 

 largely the result of the metabolism of the proteins of the 

 food, of " exogenous " protein metabolism, and that the creatinin 

 and uric acid nitrogen and neutral sulphur (p. 564) are chiefly 

 the result of " endogenous " protein metabolism. 



2. Sulphur-containing Bodies. 



The sulphur excreted in the urine is derived from the 

 sulphur of the protein molecule, and the amount of sulphur 

 excreted may be taken as a measure of the amount of protein 

 decomposed. 



A. Acid Sulphur. — The greater part of the sulphur is fully 

 oxidised to sulphuric acid. 



(a) Preformed Sulphates. — The greater part of this is 

 linked with bases to form ordinary inorganic sulphates. 



(h) Ethereal Sulphates. — Nearly all of the remaining sulphur 

 is in organic combination, linked to benzene compounds, formed 

 by oxidation of the indol, skatol, and phenol (see p. 330), which 

 in carnivora are produced by the putrefaction of proteins in the 

 bowel, and in herbivora from the aromatic compounds which 

 occur chiefly in the roughage of the food. 



Indol is oxidised into indoxyl thus — 



, X O— H 



'CeHJ 



/ 



NH 



This, when linked to potassium sulphate, forms potassium 

 indoxyl-sulphate or indican. 



/" ,O.SO.,OK 



\ // 

 NH 



From skatol, which is methyi-indol, potassium skatoxyl- 

 sulphate is formed in the same way. 



These bodies are colourless, but when oxidised they yield 

 pigments— indican yielding indigo blue, skatoxyl-sulphate of 

 potassium yielding a rose colour. 



