EXCRETION OF MATTER FROM THE BODY 401 



When Dioxybenzene or Pyrocatechin is formed in the body, 

 it too is linked to sulphate of potas- 

 sium and excreted. When urine 

 containing this substance stands, it be- 

 comes oxidised and yields a greenish 

 brown or black pigment. 



B. Neutral Sulphur. A small quantity of sulphur is some- 

 times excreted in a less oxidised state, in the form of neutral 

 sulphur. The most important compound of this kind is 

 cystin, the disulphide of amido-propionic acid, two molecules 

 of amido-propionic acid linked by sulphur 



Amido-propionic acid 



i 



Sulphur 



I 

 Sulphur 



i . 



Amido-propionic acid 



In some individuals and in certain conditions of the meta- 

 bolism not yet fully understood, the amount of cystin is 

 increased, and it then tends to crystallise out in peculiar 

 hexagonal plates. 



III. Phosphorus-containing Bodies. 



The phosphorus in the urine is derived partly from phos- 

 phates taken in the food, and partly from the nucleins of 

 the food and tissues and from the bones. 



(a) Normally the phosphorus is fully oxidised to P 2 5 , 

 which is linked to alkalies and earths, and excreted in the 

 urine. The most important phosphate is the phosphate of 

 soda, NaH 2 P0 4 , which is the chief factor in causing the 

 acidity of the urine. About one quarter of the phosphoric 

 acid is linked to lime and magnesia, and it is these earthy 

 phosphates which precipitate when the urine becomes 

 alkaline. When the urine becomes ammoniacal, triple 

 phosphate is formed (p. 396). 



(b) It is probable that a small quantity of the phosphorus 



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