202 PHYSIOLOGY OF NUTRITION 



ferrous sulphate takes place in the absence of oxygen. On the other hand, 

 the presence of ferric hydrate in a soil indicates an adequate supply of oxygen 

 for plant growth. 



Various simple plant forms always abound in soil and water that lack 

 oxygen. Since the absorption of free oxygen is impossible under such condi- 

 tions, the energy requirements of these organisms must be supplied by processes 

 other than those of simple oxidation. As a matter of fact, such processes— 

 which are those of fermentation, in general — do occur in organisms that exist 

 without free oxygen. 



It is well known that energy is liberated by the decomposition of many 

 organic substances in other ways, as well as by oxidation processes. Berthelot 1 

 showed that formic acid is decomposed by platinum black, into carbon dioxide 

 and hydrogen, with liberation of heat, the reaction being represented by the 

 equation: 



Carbon Hydro- 

 Formic acid dioxide gen 



HCOOH = C0 2 + H 2 . 



On the basis of this observation he concluded that heat production may occur 

 in living organisms without any relation to oxidation processes. 



Oxidation, 6 with liberation of heat, may occur also in the absence of molecular 

 oxygen, this element being derived from water. Wieland 2 showed that, in the 

 presence of palladium-black, aldehydes are oxidized by water, to form the corre- 

 sponding acids. Hydrogen is liberated and absorbed by the palladium black. 

 The reaction is represented as follows: 



Hydro- 

 Aldehyde Water Acid gen 



R-COH + H 2 = R-COOH + H 2 . 



Loew 3 showed that much hydrogen is freed from an alkaline solution of formalde- 

 hyde in the presence of cuprous oxide, formic acid being formed. This reaction 

 explains the formation of fatty acids, with evolution of hydrogen, by anaerobic 

 bacteria. These bacteria effect oxidation in the absence of molecular oxygen, 

 deriving this element from water. Favorskii 4 cites a series of oxidations of 

 organic compounds at the expense of water. 



Finally, oxidation in the absence of free oxygen may occur as the result of 

 the removal of hydrogen from a molecule, so as to form carbon dioxide. Thus 

 by the action of sunlight on a mixture of formic acid and quinone, Ciamician 



i Berthelot, Marcelin, Sur le synthese de l'acide formique. Compt. rend. Paris, 59 : 616-618. 1864. 

 Idem, Sur l'acide formique. Ibid. 59 : 817-819. 1864. Idem, Sur la d6composition de l'acide formique. 

 Ibid. 59: 861-865, 901-904. 1864. 



2 Wieland, Heinrich, Studien iiber den Mechanismus der Oxydationsvorgange. Ber. Deutsch. Chem. 



Ges, 4S ;/ : 2606-2615. 1912. 



3 Loew, O., Ueber einige katalytische Wirkungen. Ber. Deutsch. Chem. Ges. 20 : 144-145. 1887. 

 < Favorskii, A. E., Ueber Isomerisationserscheinungen in den Reihen der Carbonylverbindungen ge. 



chlorter Alcohole und haloidsubstituirter Oxyde der Aethylenekohlenwasserstoffe. (Original in Russian- 

 St. Petersburg, 1895.) Rev. in. Jour, prakt. Chem. Si: 533-563. 1895. Rev. also in Bull. Soc. Chim. 

 Paris 14: 1 188-1206. 189S. 



b This and the next following paragraph are introduced from the 7th Russian edition.— Ed. 



