l88 PHYSIOLOGY OF NUTRITION 



the spKtting off of hydrogen to form water or by some other oxidizing reaction. 

 An example of a reaction in which water participates is furnished by the work 

 of Wieland^ on the oxidation of alcohol to form acetic acid by living or dead 

 acetic bacteria in an oxygen-free atmosphere but in the presence of methylene 

 blue (M). This reaction is represented by the equation: 



CH3CH2OH (ethyl alcohol) + H2O + 2 M = CH3COOH (acetic acid) + 2 M-H2. 



It is possible, also, for water to be formed as a result of the union of hydrogen 

 with an acceptor of hydrogen; for example, with potassium nitrate as acceptor, 

 as represented by the equation: 



R-H2 + KNO3 = R + KNO2 + H2O. 



It follows that, after reduction, the molecule of the acceptor of hydrogen 

 may become either richer by two atoms of hydrogen (methylene blue) or 

 poorer by one atom of oxygen {potassium nitrate). 



The action of reductase, in causing anerobic oxidation by means of the 

 sphtting off of hydrogen, may be accompanied by the production of carbon 

 dioxide. Thus Bredig and Sommer^ showed (see page 180) that, in the presence 

 of a catalyzer and of methylene blue, formic acid is decomposed into carbon 

 dioxide and hydrogen: 



HCO2H (formic acid) + M = CO2 + M-H2. 



Until recently the presence of reductase in plants was determined on the 

 basis of the effect produced upon various acceptors of hydrogen. If no effect 

 on these acceptors was observed reductase was inferred to be absent, but this 

 is not correct. In addition to a hydrogen acceptor there must be present a sub- 

 stance that may be oxidized, in order that the reductase may act. This was 

 shown by Harden and Norris,' who found that reductase makes itself evident, 

 in the dried yeast of Lebedev, only after the addition of both an oxidizer and 

 a reducer. 



Various bacteria and moulds {e.g., the Mucoracese), as well as yeasts, pro- 

 duce alcoholic fermentation. Moulds generally form thick masses of mycelium 

 upon the surface of the substratum and usually absorb considerable oxygen from 

 the air. If the mycelium of such a mould is submerged in a fermentable liquid 

 alcoholic fermentation occurs, and the further development of the mycelium in 

 the liquid is very characteristic. The long hyphae divide to form cells that are 

 very similar to those of yeast. It has recently been shown that the most active 

 of these mucor yeasts produce alcoholic fermentation even in the presence of an 

 abundance of oxygen,* just as do ordinary yeasts. 



1 Wieland, Heinrich, Ueber den Mechanismus der Oxydationsvorgange. Ber. Deutsch. Chem. Ges. 

 46'": 3327-3342. 1913. 



' Bredig and Sommer, igio. [See note 2, p. 180. ] 



' Harden, Arthur, and Notris, Roland Victor, The reducing enzymes of dried yeast (LebedeS) and o£ 

 rabbit muscle. Biochem. jour. 9 : 330 — 336. 1915. 



' Kostytschew, S., Untersuchungen uber die Atmung und alkoholische Garung der Mucoraceen. Cen- 

 tralbl. Bakt. II, 13: 490-S03. 1904. Wehmer, C, Versuche fiber Mucorineeng&rung. Ibid. II, 14: 

 556-572- 190S. Idem, same title. Ibid. II, is : 8-19. 190$. 



