RESPIRATION AND FERMENTATION 269 



All these various forms of fermentations, to which until 

 recently was attributed a quite different chemical procedure, are 

 regarded by Kostytchev as connected with one another and with 

 alcoholic fermentation, showing only certain deviations from the 

 fundamental process. In all fermentations there are formed in 

 the first place pyruvic acid and hydrogen. In alcoholic fermenta- 

 tion the pyruvic acid splits up, under the influence of carboxyl- 

 ase, into acetaldehyde and CO2. In the bacteria of lactic-acid 

 fermentation, carboxylase is absent, therefore the above-men- 

 tioned cleavage does not take place. The active hydrogen com- 

 bines with the carbonyl group of pyruvic acid, reducing it to lactic 

 acid according to the equation 



CH 3 • CO • COOH + 2H -> CH 3 • CHOH • COOH. 



In impure cultures of lactic bacilli, carboxylase may be present but 

 in very small quantity. As a result, a mixture of different prod- 

 ucts of fermentation is obtained. 



With butyric-acid fermentation, on the contrary, the reaction 

 leading to the reduction of the acetaldehyde is checked by the 

 active hydrogen. The combination of 2 molecules of acetalde- 

 hyde, through aldol, into butyric acid according to the following 

 formula is obtained: 



2CH 3 • CHO -> CH 3 • CHOH • CH 2 • CHO 



-*CH 3 CH 2 CH 2 COOH. 



The hydrogen has nothing to combine with and as a consequence is 

 eliminated. 



Acetic-acid fermentation also passes through the acetaldehyde 

 stage. The hydrogen, however, is oxidized by atmospheric 

 oxygen into water, while the acetaldehyde, with the addition of 

 water, is transformed into alcohol and acetic acid: 



2CH3CHO + H 2 -^CH 3 CH 2 OH + CH3COOH. 



Thus, Kostytchev's scheme enables us to group all forms of fer- 

 mentation into one interrelated system. 



83. Connection between Fermentation and Respiration. The 

 Chemistry of Physiological Oxidation. — It has already been 

 pointed out that higher organisms, when transferred into an oxy- 

 gen-free air, display anaerobic respiration, which in its main fea- 



