THE METABOLISM OF THE PURIN BODIES 421 



(mainly as uric acid), which are destroyed in the liver but excreted 

 by the kidneys, the relative amounts destroyed and excreted' 

 depending on the relative amount of blood circulating through 

 these two organs. 



This explanation can at once be accepted for purins injected 

 into a peripheral vessel, but at first sight it seems difficult to 

 understand on the same basis why exogenous purins, which 

 during their absorption must pass through the liver before getting 

 to the kidneys, should behave quantitatively, with regard to ex- 

 cretion, like endogenous ones. The fact that the same fraction of 

 purin-N reappears in the urine of dogs after thymus or pancreas 

 feeding, hypoxanthin feeding and hypoxanthin or uric acid injec- 

 tion, but that, when uric acid is given in the food none of it can 

 be recovered as purin-N in the urine, seems to show that, before 

 their destruction in the liver, the purins must be converted into 

 uric acid. Thus, when uric acid is given in the food, it becomes 

 entirely destroyed before it enters the systemic circulation ; when 

 injected subcutaneously, however, part of it is carried to the 

 kidneys and excreted, the rest to the liver and is destroyed. 

 When purins other than uric acid are given by the mouth, they of 

 course also pass through the liver, in which however they are not 

 destroyed, 1 but pass on to the tissues, where they are converted 

 into uric acid, and then the same fractions are destroyed and ex- 

 creted as if uric acid itself had been injected subcutaneously. 



In support of this view, Burian and Schur have performed 

 some experiments in which the amount of blood circulating in 

 the kidneys was increased in proportion to that perfusing the 

 liver (e.g. by administering diuretics) ; and, as a result, have 

 obtained an increased purin excretion. As it is possible to cause 

 the dilatation of the renal vessels only for short periods of time, 

 the urine in these experiments had to be examined every, hour ; 

 in twenty-four hours the hourly increase would have been 

 followed by a succeeding decrease, and very little difference from 

 the daily excretion under normal conditions could be noticed. 

 Grape-sugar and urea in amounts varying from 3-8 grm. and 



1 In this connection it should be mentioned that an alcoholic precipitate of 

 one liver extract when added to another liver extract causes a rise in the urea 

 produced. Chassevant and Kichet argue from this that the liver can also 

 destroy purin (nuclein) bases, for the proteid in the precipitate could be no 

 precursor. This purin is, however, most probably oxidised to uric acid before 

 being destroyed. 



