URIC ACID. 909 



account for the whole of the urea excreted by the kidneys ; they consider, 

 therefore, that it must be partly formed in other organs. 



Uric acid. In those animals in which the ultimate product of 

 nitrogenous metabolism is uric acid instead of urea, it is probable that 

 the primary changes which go on in the muscles result in the formation 

 of similar substances (lactic acid and ammonia) as are formed as 

 antecedents of urea, and that the secondary change to uric acid occurs 

 in the liver. For, after extirpation of the liver in birds, these substances 

 are found in the urine replacing uric acid. 1 



Minkowski 2 removed the liver in geese, taking advantage of the fact that 

 in birds there exists a vein (Jacobson's vein) which effects a communication 

 between the portal vein and the vena advehens of the kidney, so that when the 

 portal vein is tied beyond this communication the blood of the mesenteric veins 

 passes through the kidneys, and is not caused to stagnate as in mammals. In 

 some animals he merely tied the portal vein, in others he completely removed 

 the liver ; these, however, only survived the operation a few hours (at most 

 twenty). The uric acid of the urine sank as the result of this operation, so that 

 from representing 60 to 70 per cent, of the total nitrogen of that secretion, as in 

 normal animals, it represented only 3 to 6 per cent., the amount of ammonia in 

 the form of lactate being correspondingly increased. The lactic acid found in 

 the urine under these circumstances is the sarcolactic which is formed in 

 muscular tissue ; it is present in even larger proportions than ammonia, so that 

 the urine is strongly acid. Altogether half the solids of the urine were formed 

 of ammonium lactate, although in the normal animal none is present. No 

 amido-acids were found in the urine, and no sulphates. The urea and creatine 

 were unaltered in amount. In the blood, lactic acid was present and also some 

 leucine and tyrosine. Urea injected into the stomach appeared as such in 

 the urine, although in the normal goose it is converted into uric acid. The 

 administration of glycine and asparagine caused a great increase in the 

 ammonia of the urine. The same effect as extirpation namely, the replace- 

 ment of uric acid by lactate of ammonia may be produced by merely tying 

 the hepatic artery in birds, 3 a result which is probably due to the fact that the 

 oxidations within the organ have been thereby so greatly interfered with, that 

 the transformation of the lactate of ammonia into carbonate and the subsequent 

 synthesis of uric acid has been prevented. That uric acid can be formed in 

 vitro from lactic acid, ammonia, and carbonic acid, has been shown by 

 Horbaczewski, who obtained uric acid by heating trichlorlactamide with urea 

 (see p. 587). 



We are, however, not justified in assuming that the uric acid which 

 is found in the urine of mammals runs a parallel course in its formation 

 with that taken in the formation of urea. For, in the first place, it is not 

 in them, as in birds, necessarily increased in amount by the ingestion of 

 proteid food, nor does it go hand in hand with the excretion of urea. 

 And whereas in birds the ingestion of the amido-acids and of ammonia 



1 v. Schroder showed that uric acid is not formed in the kidneys in birds and snakes, 

 but that after the removal of those organs it accumulates in the blood and tissues (Arch. f. 

 PhysioL, Leipzig, 1880, Suppl. S. 113; Beitr. z. Physiol. C. Ludwig z. s. 70 Geburtst., 

 Leipzig, 1887, S. 89). v. Schroder also showed, in confirmation of an earlier observation of 

 Meissner, that the liver of birds contains more uric acid than the blood. According to 

 A. Garrod (Proc. Roy. Soc. London, 1893, vol. liii. p. 478), there is no uric acid normally 

 in birds' blood, and this contains as much urea as that of a mammal. Garrod is of opinion 

 that uric acid is produced in the kidneys by synthesis of urea and glycine. If the results 

 of v. Schroder are correct, it is difficult to understand this conclusion. 



*Arch.f. exper. Path. u. PharmakoL, Leipzig, 1886, Bd. xxi. S. 41. 



3 Minkowski, ibid., 1893, Bd, xxxi. S. 214. 



