416 THE METABOLISM OF THE PURIN BODIES 



blood, and that, as it is produced, it is excreted into the urine. 

 All other purins in the body (e.g. of exogenous origin) are de- 

 stroyed in the various organs and tissues, so that the blood is 

 purin-free. 



(2) Hoppe-Seyler*s hypothesis : that most of the organs in the 

 body can both form and destroy uric acid, the balance of these 

 two processes being such that no uric acid escapes into the blood. 

 The kidney is also endowed with the power of forming uric acid 

 which, instead of destroying, it excretes. 



(3) Von Noor den's hypothesis : that endogenous uric acid is 

 shed into the blood as some compound, which is more stable than 

 uric acid itself (i.e. exogenous uric acid), and which is, therefore, 

 not decomposed by the tissues. 



None of these hypotheses, however, is correct, and some other 

 explanation must be offered to satisfy all the observed facts. 

 In our foregoing description of the behaviour of different 

 animals to purin administration we have assumed that the 

 endogenous moiety of purins has the same integral factor as 

 the exogenous. If this be correct, it must follow that both 

 endogenous and exogenous purin substances are intermediary 

 bodies in metabolism, and it cannot be true, as von Noorden 

 has suggested, that endogenous purins differ from exogenous in 

 that they are more stable, and so are not further decomposed. 

 We must before going further, therefore, retrace our steps and 

 see what direct evidence is to hand, showing that endogenous 

 purins are destroyed in the body, i.e. that they are not end 

 products of metabolism but only intermediary ones. 1 After 

 joining the portal vein to the vena cava in dogs, and so pre- 

 venting the portal blood from directly perfusing the liver ( 24 ) 

 it has been stated that the uric acid excretion is higher than 

 normal, even when the dogs are fed on a purin-free diet. 2 

 As will be shown later, the liver is the main seat of uric 

 acid destruction in dogs, so that its partial removal from the 

 systemic circulation, as in the above experiment, might have 

 caused less endogenous purins to be destroyed than normally. Of 

 course, it could be advanced as an objection to this proof, that the 



1 We have already had occasion to consider this question from another point 

 of view. 



2 Raskins, Herrick, and the author have been unable to confirm this high 

 endogenous purin excretion in two Eck's fistula dogs. 



