Bacterial Metabolism 63 



About 1925, after the main physiological groups of bac- 

 teria had been discovered and their more conspicuous 

 chemical activities had been determined, a new interest be- 

 gan to develop among microbiologists, that of finding out 

 something about the chemical mechanisms of oxidative and 

 fermentative processes. This interest was greatly stimulated 

 by the work of the biochemists Harden, Neuberg, Meyer- 

 hof, and others, on alcoholic and lactic fermentations and 

 respiratory mechanisms in yeast and muscle. Kluyver and 

 his associates in Holland and Fred and Peterson and others 

 in the United States gave particular attention to the com- 

 parable bacterial processes, including the lactic, propionic, 

 butyric, acetone-butanol, and other fermentations. 



The main method used by the microbiologists was that 

 of the balance experiment. Careful quantitative analyses 

 were made of the products of fermentation caused by grow- 

 ing bacterial cultures. On the basis of the data obtained 

 with various substrates such as glucose and pyruvate, an 

 attempt was made to determine the most probable of 

 several alternative mechanisms which could be suggested 

 to account for the fermentation products. This method 

 yielded a great deal of quantitative information of per- 

 manent value about bacterial fermentations. It also re- 

 sulted in the elimination of several theories of a speculative 

 character concerning the mechanism of fermentations that 

 were inconsistent with the quantitative data. The balance 

 experiment method, however, was incapable of solving the 

 problems of intermediary metabolism because it provided 

 too little information concerning what actually goes on 

 within bacterial cells, and left too much to speculation 

 based mainly on a limited knowledge of the enzymatic re- 

 actions occurring in yeast and muscle. 



One of the very important developments on the con- 

 ceptual level at this time was the recognition, particularly 

 by Kluyver and his associates, of a general similarity in the 

 metabolic processes of various microorganisms. During the 



