68 PHYSIOLOGY OF BACTERIA 



come only from the decomposition of organic or inor- 

 ganic compounds. 



Fermentation (in the broadest meaning of the term) 

 is not absolutely connected with living organisms. The 

 vinegar fermentation can be accomplished by finely 

 divided palladium in the same way as by bacteria. 

 Fermentation may be accomplished by cells after their 

 death, i.e., after loss of reproduction. The fermenting 

 agent could be separated from the cell in some instances. 

 We are forced to the conclusion that fermentation is 

 brought about by enz3rnies. 



A number of different enzymes are necessary to bring 

 about fermentation. We are at present quite unable to 

 state how many different kinds are needed. Each fer- 

 mentation is not one single process, but a combination 

 of a number of different simple chemical reactions. 



The fermentation mechanism of different genera and 

 species does not involve absolutely different reactions. 

 Different combinations of the same simple steps in the 

 gradual breakdown of the food molecule may lead to 

 quite different fermentation products. These differ- 

 ences in combination may be caused by differences in 

 pH, by the entering of other compounds into the reaction 

 (such as oxygen), and by differences in the arrangement 

 of the enzyme molecules in the cell. 



Most of these reactions can be explained best by 

 the assumption that the enzymes of the cell act upon the 

 substrate by activating certain hydrogen atoms. These 

 then combine with a ^'hydrogen acceptor.'^ The accep- 

 tor might be another part of the same molecule, or 

 another organic or inorganic molecule, or oxygen. 

 Oxygen, in order to function as hydrogen acceptor, 

 must be activated by a complex iron compound. 



