OXIDATION 63 



dioxide as is too often supposed, an idea having its origin in 

 the lungs of an animal being termed the organs of respiration. 

 Respiration is essentially a catabolic process, and any organ 

 of a plant or of an animal which is doing work is an organ 

 of respiration in that it cannot accomplish its task without 

 the energy obtained by the exertion of appropriate mechanisms. 

 The lungs and the respiratory tract, on the one hand, and the 

 stomates, lenticles, " respiratory chamber," and the intercellular 

 space system on the other, are strictly comparable : they are 

 organs of breathing ; structures, reservoirs, and surfaces for a 

 preliminary of respiration, the conveyance and initial absorption 

 of oxygen, and for the ultimate elimination of the gaseous 

 waste of physiological combustion. 



This motive power commonly is obtained by the physio- 

 logical combustion of carbohydrate, by which, theoretically, a 

 molecule of sugar is completely oxidized by 6 molecules of 

 oxygen giving origin to 6 molecules each of carbon dioxide 

 and water with the liberation of a considerable quantity of 

 energy. 



But oxidation is not quite the simple operation as might 

 be supposed from the foregoing statement. Thus the expres- 

 sion CO + O = CO. 2 may be a true statement of the result of 

 the complete oxidation of carbon monoxide to carbon dioxide, 

 but it does not necessarily represent the mechanism by which 

 the change is effected ; as a matter of fact it has been shown 

 by Wieland * and others that water is an essential in the pro- 

 cess and the first phase is an hydratiori which leads to the 

 formation of formic acid. 



CO + H 2 = H C 



Interaction between the formic acid and oxygen then takes 

 place, leading to the production of water and carbon dioxide, 

 HCOOH + o = H 2 o + co a 



It will, however, be seen that the resultant of these two reac- 

 tions is correctly expressed by the equation CO + O = CO 2 . 

 From considerations such as these, together with the fact 

 that oxidative processes enter largely into the energy-obtaining 



* Wieland, " Ber. deut. chem. Gesells.," 1912, 45, 679, 2613, where earlier 

 literature is also quoted. 



