RESPIRATION AND FERMENTATION 271 



diminish rapidly, since their harmony has been disturbed. Among 

 the various substances which accumulate under these conditions, 

 alcohol may be usually observed, whence it follows that the pri- 

 mary stage of respiration really represents alcoholic fermentation. 

 The oxidation processes following decomposition, and proceed- 

 ing under participation of air, have received differe.irt interpre- 

 tations by various authors. According to Palladin's original 

 theory, slightly altered by Kostytchev, these reactions are caused 

 by oxidizing enzymes or oxidases. The most thoroughly investi- 

 gated ones are the enzymes oxidizing various aromatic compounds 

 of the phenolic type, such as hydroquinone, tyrosin, etc. Accord- 

 ing to the idea of Chodat and Bach, the operative mechanism of 

 oxidase consists of a peroxide, oxygenase, and a special enzyme, 

 peroxidase. Under action of the oxidase system the peroxide 

 decomposes into atomic oxygen, which has the power to oxidize 

 other compounds; and a reduced fraction, which is able to unite 

 again with molecular oxygen. The oxidase system is therefore a 

 carrier of oxygen to substances which by themselves are incapable 

 of being oxidized in air by molecular oxygen. 



More detailed investigations on oxydases have shown, how- 

 ever, that their role in oxidation is very limited. They can oxi- 

 dize only a very few substances, chiefly phenolic compounds. 

 This seems to be a simple union with oxygen, further decomposi- 

 tion of the substance, with the formation of carbon dioxide, does not 

 usually take place. This forced Palladin to introduce some alter- 

 ations into his theory of respiration. He accepted the view that 

 substances oxidized by the oxidases are merely carriers of atmos- 

 pheric oxygen to the respiratory material. As the materials 

 themselves are colorless, while the products of their oxidation 

 are colored, Palladin named the former respiratory chromogens 

 and the latter respiratory pigments. 



Further studies have shown that the oxidation of many chromo- 

 gens consists not in the union with oxygen, but in the elimination 

 of hydrogen. Methylene blue is one of a number of this kind of 

 pigments. It is capable of participating in oxidizing processes, 

 though it does not contain oxygen. Its colorless compound dif- 

 fers from the pigment not by the absence of oxygen but by the 

 presence of 2 atoms of hydrogen. Still it is possible to oxidize by 

 means of methylene blue in an oxygen-free atmosphere. Thus 

 alcohol, for instance, may be oxidized to acetic acid by using acetic 



