SECTION VII. 

 EXCRETION OF MATTER FROM THE BODY. 



I. EXCRETION BY THE LUNGS (see Respiration.p.olS etseq.). 



II. EXCRETION BY THE BOWEL (see p. 361). 



in. EXCRETION BY THE KIDNEYS. 



I. URINE. 



I. General Consideration. 



The urine is a fluid formed in the kidneys, and in it are 

 excreted from the body — 



1. The nitrogen, sulphur, and phosphorus containing pro- 

 ducts of the catabolism of proteins and of nucleo-proteins of the 

 body and of tlie blood. 



2. Any excess of H or OH ions in the blood. 



3. Any excess of certain substances taken with food or 

 produced in the body, e.g. sugar and sodium chloride, 



4. Various drugs. 



Its composition should be studied in the light of the 

 catabolism of proteins and nucleo-proteins. 



{In reading this fart, the Table on pp. 568 and 569 

 should he constantly referred to.) 



1. Catabolism of Proteins. — As already indicated, the pro- 

 tein molecule breaks down into its constituent amino-acids 

 (p. 16), and these are de-aminised chiefly in the liver (p. 359). 



The ammonia liberated, probably as ammonium carbonate, is 

 dehydrated chiefly in the liver (p. 359) to form urea — 



554 



