488 VICTOK C. MYEES ^ 



total nitrogen 13.8 grams. If allowance is made for a fecal nitrogen 

 excretion of 1.5 grams, the nitrogen intake would be 15.3 grains, which 

 corresponds to about 95 grains protein. The output, of creatinin for the 

 average human adult is about 1.5 grams and of uric acid 0,5 gram. 



Urea. Urea, ammonia and amino acids are intimately related in their 

 physiological history. It will be recalled that the amino-acids, resulting 

 from the digestion of protein in the intestine, are absorbed and carried 

 to all the tissues of the body. The greater part of the amino-acids thus 

 absorbed and disseminated are deaminized, i.e., the amino group (NH 2 ) 

 is split off, forming ammonia. This process of deaminization may be illus- 

 trated as follows, taking alanin as a typical amino-acid: 



NHo OH 



I I 



CH 3 . CH . COOH + HOH - NH 3 + CH 3 . Oil . COOH 



Alanin Water Ammonia Lactic Acid 



The ammonia unites with the carbonic acid of the blood and tissues to 

 form ammonium carbonate. Two molecules of water are then split off 

 from the ammonium carbonate, yielding urea. The formation of am- 

 monium carbonate and its subsequent dehydration to form urea are Indi- 

 cated below: 



OH NH 3 OISTH 4 NH 2 H 2 O 



I I I 



C = O+ -> C = O - C = O h 



I I I 



OH NHj, OXH 4 NH a H 2 



Carbonic Ammonia Ammonium Urea Water 



acid ) Carbonate 



Kossel and Dakin have also shown that arginin may be directly 

 split into ornithin and urea under the action of a liver enzyme, arginase. 

 The deaminization of amino-acids and the transformation of ammonium 

 carbonate into urea takes place in the liver and possibly in other tissues. 

 (See preceding article, p. 464.) Because of the prominence played by the 

 liver cells in these processes, considerable importance has been attached 

 to apparent abnormalities in the elimination of urea, ammonia and amino- 

 acids. In acute yellow atrophy of the liver, interstitial hepatitis and 

 cirrhosis of the liver, there is a very extensive degeneration of the liver 

 cells. The association of hepatic disturbance with increased elimination 

 of ammonia and amino-acids, and diminished output of urea has not bpen a 

 constant finding (Fiske and Karsner), and in many instances has been ' 

 the result of employing old and inadequate methods. However, there is 



