BACTERIAL RESPIRATION 195 



Certain areas of these interfaces are endowed with activity 

 as a result of the arrangement of the molecules composing 

 them ; certain arrangements of polar groups in the 

 molecules set up local electric fields of varying intensity 

 depending on the particular molecular arrangement. 

 Any molecule, especially one containing polar groups, 

 like — CO OH, =C0, or double bonds, coming into close 

 contact with such an active surface by adsorption becomes 

 distorted with a resulting shift of the hydrogen atoms 

 rendering the molecule unstable or activated. For 

 instance, a double bond is supposed to be activated 

 according to the scheme : — 



— CH=CH > _c— CHo— 



or an aldehyde group in this way : — 



— CH = o — > _c_OH. 

 The presence of a polar group like carboxyl in a molecule 

 favours a concentration of hydrogen in its direction : — 



R— CH=CH— COOH > R— C- 



whilst a non-polar group like methyl favours a concentra- 

 tion of hydrogen away from it : — 



\/ 

 R— CH=CH— CH3 > R.CH2— C— C'Hg. 



The mechanism, as described so far, suggests how a 

 compound can be activated to act as a hydrogen donator 

 or acceptor, but it does not account for specificity. For 

 instance, it affords no explanation of the fact that Esch, 

 coli activates glucose whilst Alcaligenes fcecalis {B.fcecalis 

 alcaligenes) does not, although both organisms strongly 

 activate lactates. Nor does it explain why succinic acid 

 is oxidised by both bacteria and muscle tissue, but that 

 formic acid is a very active hydrogen donator in presence 

 of bacteria but quite inactive with muscle. This activity 

 is held to be due to the presence of definite groupings 

 of molecules in the active centres of the cells which 



