ABSORPTION 359 



nucleins. The fat of the liver thus plays an important 

 part in retaining and fixing phosphorus in the body. 



(2) Change in Liver. — The fats of the liver have a higher 

 iodine value than the fats of adipose tissue, i.e. they are less 

 saturated, and the theory has been advanced that this 

 indicates that in the liver the first stage in the breaking 

 down of fats takes place, in preparation for their use in the 

 muscles. When the fatty acid chain has two hydrogens 

 removed at any point so that a double link between carbon 

 atoms is formed, this becomes a weak point in the chain at 

 which the higher acids are apt to break across with the 

 production of lower acids. 



Lower fatty acids, liberated by the de-aminisation of certain 

 amino-acids from proteins, e.g. leucin, tyrosin, phenyl-alanin 

 are not changed to glucose (p. 354) but to j8-oxybutyric acid, 

 which is oxidised. 



3. Regulation of the Supply of Proteins. — The part played 

 by the liver in the storage of the surplus amino-acids formed 

 from proteins and in their de-aminisation, and the conversion 

 of the amidogen to urea, has already been indicated (p. 349). 

 When the supply of amino-acids is too large, or when the 

 liver is not acting properly in grave hepatic disease, this 

 conversion takes place imperfectly and amino-acids appear 

 in the urine. 



Urea is the bi-amide of carbonic acid. 



It contains 46 '6 per cent, of nitrogen. It is a white sub- 

 stance crystallising in long prisms. It is very soluble in 

 water and alcohol — insoluble in ether. With nitric and 

 oxalic acids it forms insoluble crystalline salts. It is readily 

 decomposed into nitrogen, carbon dioxide and water by 

 nitrous acid and by sodium hypobromite in excess of sodium 

 hydrate (Cheviical Physiology). 



