THE URINE 379 



The following syntheses appear to take place in different organs of the 

 body, especially in the liver: 



CH C.OH 



x \ / \ 



Indol, C e H 4 CH passes after absorption into indoxyl, C 6 H 4 CH, 



NH VH X 



and this body then unites with sulphuric acid into indoxyl-sulphuric acid, urine 



indican, C 6 H 4 CH 



Nra 



In an exactly similar way there arise from skatol or methyl-indol, 



C.CH, C.CH 



x \ / \ 



CJI 4 CH, first skatoxyl, C 6 H 4 C.OH, and then, skatoxyl - sulphuric 



NH C.CH NH 



/ \ 



acid, C 6 H 4 C.O.SO a (OH) ; from phenol, C fl H 6 .OH, phenol-sulphuric acid, 



NH QH 



C 6 H 6 .O.SO a (OH) ; from paracresol, C 6 H 4 N pTT paracresol-sulphuric acid, 

 X).SO,(OH) 



If the sulphuric acid available is not sufficient for the combination of the 

 phenols, they are paired with glycuronic acid (page 376). This acid is an inter- 

 mediary product of metabolism and is further decomposed except when it is 

 protected from combustion by pairing with other substances. 



We have already studied the processes of excretion in the intestine, in the 

 liver and in the lungs. There remains for us to discuss excretion through the 

 kidneys and the skin. 



FIRST SECTION 



THE URINE AND ITS EXCRETION 



1. THE URINE 



The urine is formed by the action of the kidneys. It contains the most 

 of the nitrogenous and sulphur-containing products of metabolism as well 

 as a large number of other substances to be eliminated from the body. 



A. THE GENERAL PROPERTIES OF THE URINE 



The reaction of a sample of urine differs according to the indicator used. 

 With phenolphthalein it is acid, with litmus acid, neutral or alkaline, with 

 methyl orange, alkaline. This difference is referable to the properties of the 

 different indicators, which, according to the theory worked out by Ostwald, rep- 

 resent weak acids or bases whose radicals as free ions possess other colors than 

 those which the electrically neutral molecules possess. Thus phenolphthalein in 



