106 A. I. RINGER 



The reaction involved is no doubt the following: The ammonia as it 

 is set free, combines with the carbon dioxid and water of the blood and 

 tissue, forming ammonium carbonate. 



/OH 

 11,0 + COo -* CO 



\on 



Water Carbon Carbonic 



dioxid acid 



/OH NII 3 /OXH 4 



CO + - CO 



\OII NIL, \ONII 4 



Carbonic Ammonia Ammonium carbonate 



acid 



The ammonium carbonate, on losing one molecule of water, is con- 

 verted into ammonium carbamate. 



/ONH, 



CO H,O - CO 



\OXII 4 \NIL 



Ammonium carbonate Ammonium carbamate 



which substance, on losing another molecule of water, is converted into 

 urea. 



/ONII 4 

 CO H 2 0. - CO 



\NH 2 

 Ammonium carbamate Urea 



In normal individuals, on normal diet, from 80 to 90 per cent of all 

 the nitrogen is excreted in the form of urea, while about 3 to 5 per cent 

 escapes in the form of ammonia. 



Thus the nitrogenous element of the protein molecule plays a com- 

 paratively simple role in the physiological economy. As long as it is at- 

 tached as an amino radical it forms one of the binding posts of the amino 

 acid; it may enter into the formation of protoplasm, it may be built up 

 into complex protein bodies, ferments, etc. ; in other words it may play an 

 important role in the life of cells. The moment it becomes dissociated it 

 becomes dead matter, ready to be cast off and excreted in the urine. 



There is no heat liberated in the transformation of proteins to the 

 amino acid stage, nor is there any heat liberated in the process of deamina- 

 tion or transformation of the ammonia into urea. 



