158 KSSENTIALS OF CHEMICAL PHYSIOLOGY 



urea and oxalic acid can be obtained from it. It is, however, doubtful 

 whether a similar oxidation occurs in the normal metabolic processes 

 of the body. 



Uric acid is dibasic, and thus there are two classes of urates the 

 normal urates and the acid urates. A normal urate is one in which 

 two atoms of the hydrogen are replaced by two of a monad metal like 

 sodium; an acid urate is one in which only one atom of hydrogen. is 

 thus replaced. The formulae would be 



C 5 H 4 N 4 0;j =uric acid 

 C 5 H 3 NaN 4 3 =acid sodium urate 



sodium urate 



The acid sodium urate is the chief constituent of the pinkish deposit 

 of urates, which, as we have already stated, is called the lateritious 

 deposit. 



If uric acid is represesented by H 2 U, the normal urates may be represented 

 by M U and the acid urates by MHU. Bence Jones, and later Sir W. Roberts, 

 considered that the urates which actually occur in urine are quadriurates, 

 MHU.H^U. There is much doubt whether such compounds actually exist ; 

 if they do they are readily decomposed into acid urates MHU and free uric 

 acid, H 2 U. 



The quantity of uric acid excreted by an adult varies from 7 to 10 

 grains (0'5 to 075 gramme) daily. 



The best method for determining the quantity of uric acid in the 

 urine is that of Hopkins. Ammonium chloride in crystals is added 

 to the urine until no more will dissolve. This saturation completely 

 precipitates all the uric acid in the form of ammonium urate. After 

 standing for two hours the precipitate is collected on a filter, washed 

 with saturated solution of ammonium chloride, and then dissolved in 

 weak alkali. From this solution the uric acid is precipitated by 

 neutralising with hydrochloric acid. The precipitate of uric acid is 

 collected on a weighed filter, dried and weighed, or titration may be 

 performed with potassium permanganate (see Advanced Course). 



Origin of Uric Acid. Uric acid is not made by the kidneys. 

 When the kidneys are removed uric acid continues to be formed and 

 accumulates in the organs, especially in the liver and spleen. The 

 liver has been removed from birds, and uric acid is then hardly formed 

 at all, its place being taken by ammonia and lactic acid. It is there- 

 fore probable that in these animals ammonia and lactic acid are 

 normally synthesised in the liver to form uric acid. 



This synthetic origin of uric acid, which is so important in birds 

 and snakes, does not, however, occur in mammals. In mammals 

 uric acid is the chief end-product of the katabolism of cell nuclei or 



