DESTRUCTION OF URIC ACID 509 



The steps by which uric acid is destroyed are not known, 

 except that in any case the nitrogen is eliminated as urea. Experi- 

 mental decomposition of uric acid in the laboratory shows that 

 it can be split up in at least three different ways. By certain 

 methods it yields glycocoll, ammonia, and carbon dioxide ; by 

 another method the products are first, alloxan (C 4 H 2 N 2 O 4 ), 

 which later yields parabanie acid (C 3 H 2 N 2 O 3 ), and this in turn 

 yields oxalic acid and urea. By still a third method uric acid 

 is decomposed into allantoin (C 4 H 6 N 4 O 3 ) and carbon dioxide, 

 and the allantoin yields, on further oxidation, urea and oxalic 

 acid, thus : 



NH CH NH NH 2 COOH 



0=0 C = + + 2H 2 = 20C + 



NH CO NH 2 NH 2 COOH 



(allantoin) (urea) (oxalic acid) 



It seems quite probable that allantoin is one of the first steps 

 in the metabolic oxidation of uric acid in the body, for if 

 excessive quantities of uric acid or of purin-rich foods are fed 

 to dogs, a large amount of allantoin appears in the urine. As 

 smaller quantities of purins are completely oxidized, it seems 

 probable that the excessive amounts cannot be completely 

 oxidized and are eliminated while in the allantoin stage. Allan- 

 toin seldom appears in human urine, except in young infants 

 and pregnant women, in both of which cases the cause may 

 be either deficient oxidation or excessive destruction of tissue 

 nucleins. However, there is also evidence that glycocoll is 

 formed in the tissues from uric acid, and hence it is possible 

 that uric acid may be broken down along more than one of the 

 lines of decomposition indicated above. In any case, however, 

 the destruction of uric acid depends upon oxidation, and is, 

 therefore, but a continuation of the process by which the purin 

 bases are converted into uric acid. 



The destruction seems to take place chiefly in the liver, kidney, 

 and muscles, extracts of these organs being capable of destroying 

 uric acid in vitro ; but little or no uric acid is destroyed in the 

 lungs, spleen, and blood. In different species of animals the 

 amount of destruction in the liver and kidney varies, in carnivora 

 the liver being most active, as shown by Burian and Schur, 

 who found that in nephrectomized dogs no uric acid appears in 

 the blood, but on excluding the liver from the circulation, uric 

 acid at once appears. In herbivora the kidneys seem to be 

 more actively uricolytic. This difference perhaps depends upon 



