ELEMENTARY PHYSIOLOGICAL CHEMISTEY 255 



vein he ligatured above this branch, the portal blood is diverted into 

 the kidneys. The liver can now be extirpated, the animal surviving 

 the operation several hours, and during this time the uric acid almost 

 entirely disappears from the urine, ammonia lactate taking its place. 

 Keasoning from analogy, then, we may suppose that urea is also formed 

 from ammonia salts in the liver of mammals. 



(3) In certain diseases of the liver e.g. acute yellow atrophy, phos- 

 phorus poisoning, marked cirrhosis the hepatic cells die and lose 

 their power of forming urea, and as a consequence of this, the urea 

 diminishes 'in the urine, ammonia salts, and even amido acids (leucin 

 and tyrosin) taking its place. 



CHAPTEE XVII. 

 URIC ACID AND THE OTHER PURIN BODIES. 



IT will be remembered, from the description of the chemical structure 

 of nuclein (p. 179), that there exist among its decomposition products 

 several bodies belonging to the so-called purin group of chemical sub- 

 stances. Uric acid is also a member of this group. The group receives 

 its name, because all the members of it contain as their nucleus of 

 construction a body called purin, which exists as a double ring of carbon 

 and nitrogen atoms. The various members of the group differ from 

 one another according to the nature and position of the various side 

 chains, which are tacked on to this purin ring. In order to make the 

 relationship clear the structural formulae of the various members 

 should be studied side by side, thus : 



J N C 6 HN CO 



II /I 



20 s C _7 N CO C NR 



I I >C 8 ; \ || 



3 N _4 C _N9/ HN C NH 



Purin. Uric add. 



HN CO HN CO 



CO C NH CH C NH 



\ || >CH; V || >CH; 



HN-C-N^ ^N C N^ 



X an thin. Hypoxanthin. 



NH CO N=C NH 2 



C(NH) C NH CH C-NH 



\ || >CH; \ || >CH; 



NH-C-N" N-C-N^ 



Guanin. Adenin. 



