132 PLANT RESPIRATION 



CH3— CO— COOH + CH3— CHO + C10H7NH0 = 



F>yruvic acid Acetaldehyde Naphthylamine 



.N=C— CH 



3 



CioHe^^ 1 +2HoOH-H2. 



^C=CH 



COOH 



Methyl naphtho-cinchoninic acid 



It is vety evident that acetaldehyde as well as pyruvic acid 

 is more easily oxidised than ethyl alcohol. Acetaldehyde 

 can probably be burned to CO2."' Still we know that by the 

 action of nitric acid on acetaldehyde not acetic acid but chiefly 

 glyoxal CHO — CHO, is formed. A combustion of glyoxal to 

 CO2 and HoO by way of glyoxylic or oxaHc acid is very practi- 

 cable. Nevertheless the hypothesis seems to be more probable 

 that other substances are to be considered as normal inter- 

 mediates of oxygen respiration, substances which are formed 

 in the first stages of alcoholic fermentation. These first phases 

 of fermentation are not yet studied and we have only purely 

 theoretical conceptions of them. We shall here disregard the 

 older theories of alcoholic fermentation, which do not take into 

 consideration the intermediate formation of acetaldehyde, and 

 consider biiefly only the modern theories. 



Kostychev's scheme is really not a theory but a compilation 

 of experimentally grounded facts which clarify only the last 

 phases of the process. By means of a series of unknown coupled 

 reactions, fermentable sugars change to two molecules of pyru- 

 vic acid and atomic hydrogen which is loosely joined to accep- 

 tors. Then follow both end reactions. First, by the action of 

 carboxylase, pyruvic acid decomposes into acetaldehyde and 

 carbon dioxide." Then the acetaldehyde is reduced to ethyl 

 alcohol by active hydrogen. 



"* For a recent study of the mechanism of oxidation of aldehyde by dehydroxy- 

 dation see Miiller, E. Ann. d. Chem. 420: 241-263. 1920. — Ed. 



" No release of energy is involved in this reaction. This is evidenced by a 

 comparison of the heats of combustion per mol of pyruvic acid and acetaldehyde. 

 For the details of this comparison see H. Blaschko. Biochem. Z. 158: 428-434. 

 1925. — Ed. 



