THE CHEMICAL COMPOSITION OF THE BODY 



37 



molecules of water split off, leaving carbon dioxide, C0 2 , the end 

 product of oxidation of carbon compounds in the body. 



HO 



HO 



Cl 



OH 



:OH 



The tendency of the carbon molecule to form rings has been men- 

 tioned ; the chief of these is the so-called benzene or carbocyclic ring, 

 which is represented as six carbon atoms linked together thus : 



C 



or 



Benzene itself is C 6 H 6 , an atom of hydrogen being linked on to 

 each carbon atom. Starting from benzene, it is possible to obtain a 

 large number of compounds, so-called aromatic compounds, a few of 

 which, such as phenylalanin and tyrosin, enter into the construction 

 of some of the body compounds. 



Or carbon may be linked with nitrogen to form a ring thus : 

 C- -0 



or 



1 1 



C C 



V 



H 



N 

 H 



Four carbon atoms linked to an = NH or imino group give the 

 pyrrhol ring. 



In other bodies the benzene and pyrrhol rings are found combined 

 together, yielding a compound ring found in such bodies as tryptophan, 

 indol, and skatol. The ring may be represented thus: 



H 



H 



