590 METABOLISM, NUTRITION AND DIETETICS 



plasm, or are liberated as the protoplasm breaks down. The first step may 

 be conceived of as the splitting off of the NH 2 group, which yields ammonia. 

 The ammonia is transformed into urea. The non-nitrogenous residue 

 after removal of the amino-group differs according to the amino-acid. 

 Some of the amino-acids, such as alanin, glycin, prolin and aspartic acid, 

 yield substances which can be changed into dextrose in the body, as shown 

 by the increased amount of dextrose excreted by phlorhizinized animals 

 when the amino-acids are fed to them.* Other amino-acids e.g., lysin, 

 histidin and tyrosin, phenylalanin, etc., have such a chemical structure 

 that the non-nitrogenous compounds derived from them cannot form dextrose. 

 From certain amino-acids, such as histidin, phenylalanin, tyrosin and 

 leucin, it has been shown that acetone bodies can be derived. These facts 

 explain how sugar can be formed and the acidosis associated with the 

 acetone bodies developed in diabetes, even when the diet consists of protein 

 only or when the patient is living on his own tissues. 



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 transuda- 

 tions 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. 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, pyruvic acid (p. 545) 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 

 increase 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, pyruvic 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, and 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 



* In animals under the influence of phlorhizin sugar is formed from all 

 substances capable of producing it in the organism. 



