512 RESPIRATION 



3. The theory of Hoppe-Seyler denies these pecuUarities of the oxygen-fraction 

 and explains this reaction upon the basis of reductions in which nascent hydrogen 

 plays a part. It is said that reducing substances are formed by the hydrolytic 

 splitting of the foodstuffs in consequence of ferment activity. The atomic hydro- 

 gen acting upon the oxygen, forms water during which process some atomic oxygen 

 is left over which is used to oxidize the split products of the fermentation. 



Traube, ^ on the other hand, advocates the view that the molecule of oxygen acts 

 in its entirety. He assumes, however, that the oxidizable substances are not 

 acted upon by free oxygen but only by the bound oxygen of the water. Thus, it 

 is stated that the molecule of water is first split into its components, oxygen and 

 hydrogen, and that the former is combined with the oxidizable body and the latter 

 with one whole molecule of oxygen to form hydroperoxid. This theory, however, 

 does not give satisfactory answer to the question of why the oxidizable substance 

 prefers bound oxygen to free oxygen and why the latter selects the hydrogen of the 

 molecule of water and not the oxidizable body. But, this theory possesses the 

 advantage of being more truly chemical, because it minimizes the atomic action of 

 oxygen and calls attention to the primary formation of hydroperoxid. Much 

 greater emphasis has been placed upon this process by Engler^ and Bach^ who be- 

 lieve that the oxygen-molecule = is incompletely split by the free energy 

 of the oxidizable one, so that — — — groups arise which combine with the 

 former under the formation of primary peroxid. Inasmuch as one-half of the 

 oxygen is contained in these peroxids in a loose and active state, it can be trans- 

 ferred without difficulty to other oxidizable substances. 



Hydrolytic oxidations include first of all those processes which are 

 accomplished with the help of the peroxid-oxygen and secondly, those 

 which are carried on at the expense of the hydroxyls of water. But, 

 the separation of the latter necessitates the presence in the substance 

 of a relatively large amount of energy consisting in an affinity for the 

 hydroxyls. Substances of this kind are few in number and hence, it 

 generally happens that two substances take part in the hydrolysis, one 

 of which attracts the hydroxyl and the other the hydrogen. As an 

 example of this type of oxidation, Bach^ cites the splitting of water 

 by hjrpophoric acid or its salts in the presence of metallic palladium. 



While the peroxid theory of combustion as such enables us to 

 explain many phenomena of life which would otherwise remain hidden 

 to us, several facts have been added to it in more recent years which 

 render it even more serviceable. Thus, it has been established that 

 the oxidations do not actually affect the substance of the cells and 

 cause its destruction, but merely take place in its presence under the 

 influence of specialized ferments. The latter, of course, are a product 

 of the cells and hence, we are dealing in this case with a chemical 

 process during which the organized cytoplasm does not suffer. As 

 an analogous reaction might be mentioned the conversion of sugar 

 into alcohol and carbon dioxid by the living yeast cell. 



The biological oxidations are slow combustions, and as such must 

 be subject to the influence of catalytic agents. In the sense of Ostwald, 

 therefore, these processes are catalyses, i.e., true reactions, instigated 



1 Chem. Berichte, xv, 1882, 659; xviii, 1885, 1877, and xviii, 1885, 1890. 



2 Ibid., XXX, 1897, 1669. 



3 Compt. rend., cxxiv, 1897, 951. 



* Chem. Berichte, xlii, 1909, 4463. 



