872 RESPIRATION AND OXIDATION. 



With these views as basis and at the same time although independently 

 of each other ENGLER 1 and BACH 2 have developed a theory which for 

 the present is the one generally accepted. According to this theory, 

 peroxides of the hydrogen peroxide type are always formed as primary 

 oxidation products. The peroxides are either formed by a direct attach- 

 ment of oxygen with readily oxidizable substances or in consequence of a 

 simultaneous oxidation with other substances in the last way, for 

 example, the formation of H2O2 in the oxidation of indigo-white to indigo 

 according to the formula: 



/H 

 Indigo^ + O2 = Indigo -f- H^Cb 



H 



Indigo-white 



Only certain substances have the ability either directly or indirectly of 

 forming peroxides. Certain protein-like substances occurring especially 

 in the plants which have this ability, have been called oxygenases by 

 BACH and CnoDAT. 3 Most of the substances which are oxidized within 

 the organism lose their ability to be directly oxidized. The oxidation 

 of such substances can, according to BACH, 4 be accomplished in that the 

 oxygen is transported to the substance to be oxidized from the peroxide 

 simultaneously present by means of special enzymes, the peroxidases. 

 These latter were first prepared from pumpkins and from horse-radish 

 roots. In the absence of peroxides or oxygenases the peroxidases are 

 without action. CHODAT and BACH 5 have also found that certain 

 preparations, which have previously been called oxidases, can be decom- 

 posed into oxygenases and peroxidases. According to BACH'S theory the 

 formation of peroxides is a constant process going on in the organism, 

 to which the organism accommodates itself, in that the cells by means of 

 the peroxidases can make use of the peroxides for the oxidation processes. 

 Besides this the organism also forms other enzymes, the so-called 

 catalases, which have the ability of decomposing the peroxides with the 

 formation of molecular oxygen (02) and in this way making a possible 

 excess of peroxides harmless. 6 In reference to the behavior of the perox- 



1 Verb, naturw. Verein, Karlsruhe, 20, XI (1896), Bd. 13, 72; see also Zeitschr. 

 f. physiol. Chem., 59, 327 (1909). 



2 Compt. Rend., 124, 951 (1897); see also Bioch. Centralbl., 1, 417, and 457 (1903); 

 9, 1 (1909). 



3 Ber. d. d. chem. Gesellsch., 36, 600 (1903). 



4 Ibid., 36, 600 (1903). 



5 Ibid., 36, 606 (1903). 



6 Bioch. Centralbl., 1, 460. 



