562 THE UKINE [GIL xxxvn. 



a filter, washed with Scaturated 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 

 the crystals may be dissolved in sodium carbonate solution, and 

 titrated with standard solution of potassium permanganate, until a 

 diffused pink flush appears throughout the solution. 



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 in these animals that ammonia and lactic acid are 

 normally synthesised in the liver to form uric acid. 



The chief conditions which lead to an increase of uric acid are : 



1. Increase of meat diet and diminution of oxidation processes, 

 such as occur in people with sedentary habits. 



2. Pathological conditions allied to gout. 



3. Increase of white corpuscles in the blood, especially in the 

 disease known as leucocythcemia. This latter fact is of great interest, 

 as leucocytes contain large quantities of nuclein. Nuclein yields 

 nitrogenous (purine) bases (adenine, hypoxanthine, etc.), which are 

 closely related to uric acid. 



The close relationship of the purine bases to uric acid has been clearly demon- 

 strated by the work of Emil Fischer, for they are all derivatives of the substance 

 called purine. The names and formulae of these substances are as follows : 



Purine C 5 H 4 N 4 



( Hypoxanthine (monoxy-purine) 



r> u Xanthine (dioxy-purine) 



Purme bases^ Ade nine (amino-purine) 



l^Guanine (amino-oxy-purine) 

 Uric acid (trioxy-purine) 



C 5 H 4 N 4 



C 5 H 4 N 4 0, 



C 5 H 3 N 4 .NH 2 



C 5 H',N 4 O.NH., 



C 5 H 4 N 4 3 



We have here a way in which uric acid may arise by oxidation from the nuclein 

 bases, and thus ultimately from the nuclei of cells. Certain forms of diet increase uric 

 acid formation by leading to an increase of leucocytes and consequently increase in 

 the metabolism of their nuclei ; in some cases, however, the increase is chiefly due 

 to nuclein in the food. Uric acid, which comes from nuclein or purine substances 

 in the food, is termed exogenous ; that which arises from metabolism is termed endo- 

 genous. Although special attention has been directed to the nuclei of leucocytes 

 because these can be readily examined during life, it must be remembered that the 

 nuclein metabolism of all cells may contribute to uric acid formation. The synthetic 

 formation of uric acid from ammonia and lactic acid, which is so important in birds, 

 occurs in mammals to a slight extent only. 



Hippuric Acid. 



Hippuric Acid (C 9 H 9 N0 3 ), combined with bases to form hip- 

 purates, is present in small quantities in human urine, but in large 

 quantities in the urine of herbivora. This is due to the food of 



