200 PHYSIOLOGY OF NUTRITION 



and Silber 1 obtained hydroquinone and carbon dioxide, according to the 

 following equation: 



Carbon 

 Formic acid Quinone Hydroquinone dioxide 



HC0 2 H + C 6 H 4 2 = C 6 H 6 2 + C0 2 . 



Bredig and Sommer 2 also obtained carbon dioxide by the action of methylene 

 blue on formic acid in the presence of a catalyzer, the reaction being: 



(C 16 H 18 N 3 S) 2 S0 4 + HC0 2 H = (C ]6 H 2 oN 3 S) 2 S04 + C0 2 . 



Fermentation processes are really processes of decomposition accompanied 

 by the liberation of heat, and they may take the place of respiration when 

 free oxygen is not absorbed. Pasteur regarded fermentation as "life without 

 oxygen." Economically these decompositions are less efficient for the organism 

 than are oxidations, for more energy is always liberated in the latter. It is 

 obvious, for example, that the oxidation of formic acid must produce a greater 

 amount of heat than does the simple decomposition of this substance into car- 

 bon dioxide and hydrogen, since the heat of combustion of hydrogen does not 

 appear in the latter case. An analogous result is reached by comparing the 

 equation representing oxygen respiration with that for alcoholic fermentation, 

 from the thermo-chemical point of view. 



Respiration: C 6 H 12 6 + 6 2 = 6 C0 2 + 6 H 2 0. 

 Fermentation: C 6 Hi 2 6 = 2 C 2 H 5 OH + 2 C0 2 . 



In the first case the total heat of combustion of the glucose is liberated, which 

 amounts to 709 kg.-cal. per gram-molecule (180 g.). The amount of heat liber- 

 ated in the second case must be less than in the first, because one of the end 

 products of fermentation is ethyl alcohol, which is easily oxidized. This alco- 

 hol gives a heat of total combustion of 326 kg.-cal. per gram-molecule, and, 

 since there are two molecules of alcohol produced from each molecule of 

 glucose, we must subtract 2 X 326 from 709, thus obtaining 57 kg.-cal. as the 

 amount of heat set free by the fermentation of a gram-molecule of glucose 

 according to the second equation given above. It follows that more than 

 twelve times as much glucose must be decomposed in fermentation as is oxidized 

 in respiration, to give equal amounts of free heat. The difference between the 

 two processes is practically even more pronounced than is thus indicated. All 

 kinds of fermentation require relatively very large amounts of material, as 

 compared with the corresponding complete oxidations. 



Fermentation consists in the decomposition of organic compounds with- 

 out the agency of atmospheric oxygen, while respiration is essentially an 

 oxidation process. The question now arises whether there may be a relation- 



1 Ciamician, G., and Silber, P., Chemische Lichtwirkungen, (I Mitteilung.) Ber. Deutsch. Chem. Ges. 

 34 7/ : 1530-1543- 1001. 



2 Bredig, G., and Sommer, Fritz, Anorganische Fermente. V. Die Schardingersche Reaktion und 

 ahnliche enzymartige Katalysen. I. Die Schardingersche Reaktion mit anorganischen Fermenten. [Re- 

 duktion von Methylenblau mit Formaldehyd durch Metallkatalyse.] Zeitsch. physik, Chem. 70: 34-65. 



Iqio. 



