METABOLISM, NUTRITION AND DIETETICS 505 



in the human subject in leukaemia. But none of these things can 

 be admitted as evidence that in the normal endogenous metabolism 

 of mammals uric acid lies on the direct line from protein to urea. 

 Kreatin exists in the body in greater amount than any of these, 

 muscle containing from 0-2 to 0*4 per cent, of it ; and the total 

 quantity of nitrogen present at any given time as kreatin is not 

 only greater than that of the nitrogen present in urea, but greater 

 than the whole excretion of nitrogen in twenty-four hours. But 

 although in the laboratory kreatin can be changed into kreatinin, 

 and kreatinin into urea, there is no proof that in the body anything 

 more than the first step in this process is accomplished. When 

 kreatin is introduced into the intestine or injected into the blood, 

 it appears in the urine, not as urea, but as kreatinin. We have 

 already seen that kreatinin is the chief nitrogenous product of 

 endogenous protein metabolism. 



Ammonia and amino-acids may also be produced from tissue - 

 protein, or it may be from ' circulating ' protein (p. 536), which 

 has not been built up into protoplasm, for proteolytic ferments are 

 everywhere found in the organs. And if ammonia and amino- 

 acids are formed in the tissues, there is no reason to suppose that 

 they will not yield urea, just as if they were produced in the 

 intestine. 



Formation of Uric Acid. Uric acid, like urea, is separated 

 from the blood by the kidneys, not to any appreciable extent 

 formed in them. In birds, and often in man, it can be detected 

 in normal blood. It is present in increased amount in the blood 

 and transudations of gouty patients, in whose joints and ear- 

 cartilages it often forms concretions. ' Chalk-stones ' may 

 contain more than half 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. It has been further shown 

 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 increase is too great to be due merely to the 

 sweeping out of previously formed uric acid from the hepatic 

 cells. There can be no question, then, that the liver in birds 

 is the seat of an extensive synthesis of uric acid from such simple 

 materials as ammonia and lactic acid. 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 for- 

 mation in birds. In both groups of animals the oxidative pro- 

 duction of uric acid takes place, not in any particular organ, but 



