BACTERIAL RESPIRATION 197 



that the action could be inhibited by low concentrations 

 of hydrocyanic acid, the concentration necessary being 

 proportional to the iron content of the catalyst . Narcotics 

 can also inhibit the reaction, and this he attributed to 

 their adsorption on the active surface preventing the 

 access of oxygen. 



Kluyver has combined the above ideas into a general 

 scheme, applicable to all fermentations, which involves 

 the transfer of hydrogen to oxygen in the case of aerobic 

 oxidations or to some other acceptor, suitably activated 

 by an enzyme, in other cases. Where oxygen is con- 

 cerned, an iron compound such as Keilin's cytochrome 

 is usually also involved. The enzymes involved in such 

 hydrogen transfers are called dehydrases, dehydrogenases 

 or hydrogen transportases. 



It is seen that all these processes are coupled oxidation- 

 reduction reactions, hydrogen being given up by the 

 substrate, the donator, and transferred to a second 

 substance, the acceptor. For the purposes of our study 

 these reactions can be divided into three types : — 



Type I. — The hydrogen acceptor is atmospheric 

 oxygen, that is, direct oxidation occurs, as is the case 

 with the production of acetic acid in the vinegar fer- 

 mentations, or the action of many moulds and of the 

 Mycobacteria on sugars. 



Type II. — The hydrogen donator and acceptor are 

 the same molecule, giving rise to an intra-molecular 

 fermentation. As an example one may take the conver- 

 sion of glucose, C6H12O6, into two molecules of lactic 

 acid, 2C3H6O3. Apparently no hydrogen or oxygen is 

 required from outside, the new compound resulting 

 from a rearrangement of the distribution of the hydrogen 

 and oxygen wdthin the molecule. Actually the process 

 is not so simple as this, since the final effect is brought 

 about by a whole series of intermediate reactions. What 

 it really amounts to is that a single substance is sufficient 

 for the growth of the organism. 



