THE METABOLISM OF THE PURIN BODIES 415 



observed ( cf. Wiener). 1 The question as to whether, by purin de- 

 struction, allantoin normally is produced in the organism, cannot, 

 therefore, be at present definitely answered. 



Still less is known regarding the possible derivation of oxalic 

 acid from purin break-down. It is probable that even were it 

 thus derived it would be as quickly oxidised as it was produced, 

 and would thus escape detection. It has, however, been found 

 increased in the urine of rabbits fed with allantoin (Luzzatto). 

 On the other hand, Salkowski ( 23 ) has recently shown that a 

 dog's liver in which uric acid is actively destroyed (as we will see 

 later) contains no more oxalic acid than does a calf's liver in which 

 no destruction of uric acid ensues. 



In man the urea excretion, as well as that of uric acid, rises 

 after feeding with pure nuclein (prepared from salmon sperm or 

 yeast, &c.), and the relationship between total N and urea-^ 

 seems to remain practically unchanged, showing that all the de- 

 composed purins are thrown out from the body as urea. Very 

 few researches have, however, been undertaken by the use of 

 modern accurate methods to confirm this important point. 



The only conclusion we can come to, from a consideration of 

 these observations, is that glycin is produced, in certain animals at 

 least, as an intermediate product of purin break-down ; and that 

 allantoin and oxalic acid may be produced during the same process 

 under certain not clearly defined conditions. 



We come now to a problem in purin metabolism which has, for 

 long, defied all solution, and can, even now, be considered only as 

 partially solved. The problem is this: why, if the organism be capable 

 of destroying purins at all, does it not entirely destroy them so that 

 the urine is purin-free f The answer to the problem is all the 

 more difficult because no uric acid or other purin body can, under 

 normal conditions, be detected in a free state in the blood. The 

 following three hypotheses have been offered in solution of the 

 problem : 



(1) Garrod's hypothesis: that (endogenous) uric acid is pro- 

 duced only in the kidneys from precursors carried to it by the 



1 Furthermore, Poduscka and Swain ( 21 ), on repeating Salkowski's experi- 

 ments of adding uric acid to the food of dogs, found allantoin to appear in the 

 urine only after very large amounts (3 grm.) of uric acid were given ; whereas, 

 with small amounts (1 grm.), none of it appeared. 



