580 METABOLISM, NUTRITION AND DIETETICS 



forms concretions. ' Chalk-stones ' may contain more than hall 

 their weight of sodium urate. 



As to the place and manner of formation of uric acid, it has already 

 been stated that in birds, after extirpation of the liver, the uric acid 

 excretion is greatly diminished, and that ammonium lactate appears 

 instead in the urine. The simplest interpretation of this result is, 

 that ammonia and lactic acid pass into the urine because they can 

 no longer be utilized for the synthesis of uric acid. Chemical 

 schemata can indeed be constructed, which show more or less 

 plausibly how lactic acid, pyuvic acid (p. 537), and other substances 

 reacting with ammonia or with the urea derived from it (and birds 

 form some urea) might yield uric acid. It has been further stated 

 that when blood containing ammonium lactate is circulated through 

 the surviving liver of the goose, an increase in the uric acid content 

 of the blood occurs. As demonstrated by control experiments, this 

 inciease is too great to be due merely to the sweeping out of pre- 

 viously formed uric acid from the hepatic cells; also the feeding of 

 lactic acid, pyuvic acid, and other organic acids leads to an increased 

 output of uric acid. The story seems fairly complete, although 

 criticisms have not been lacking. It has been suggested, for instance, 

 that for some reason the loss of the liver leads to acidosis, an in- 

 creased production of acids, especially lactic acid, in the organism: 

 that ammonia, which would otherwise be employed in the formation 

 of uric acid, is needed to neutralize these acids, arid that the appear- 

 ance of this ammonia in the urine is only a secondary consequence 

 of the elimination of the liver. The deficiency in the uric acid 

 excreted, it is said, is therefore due, not to inability on the part of 

 the remaining tissues to form uric acid, but to the absence of the 

 ammonia which they require for its formation. This criticism, if 

 it were admitted as against the current interpretation of such ob- 

 servations on the bird's liver, could scarcely be denied some validity 

 as against the current interpretation of similar observations on the 

 results of interference with the mammalian liver. It is therefore 

 important to point out that there is still the same deficiency of uric 

 acid when alkali is administered to neutralize the acids, although 

 ammonia ought now to be available. (There can be no question, 

 then, that the liver in birds is the seat of an extensive synthesis of 

 uric acid,) and there is little doubt that ammonia compounds are 

 essentially concerned in the process, whatever the role of the lactic 

 or other acids may be. f A similar synthetic formation of uric acid 

 from ammonia and a derivative of lactic acid may take place in 

 mammals, and probably exclusively in the liver, but it is of much 

 less importance. Another way in which uric acid arises both in 

 mammals and in birds is by the splitting and oxidation of nucleins 

 This is by far the most important mode of formation in mammals,} 

 as synthesis is the chief mode of formation in birds. In both groups 



