64 Perspectives in Microbiology 



exploratory period a great variety of metabolic processes 

 were discovered which on superficial examination appeared 

 to be wholly unrelated. For example, most microbiologists 

 of thirty years ago saw little connection between the utiliza- 

 tion of oxygen by the acetic acid bacteria for the conversion 

 of alcohol to acetic acid and the formation of hydrogen 

 sulfide by the sulfate-reducing bacteria. Kluyver pointed 

 out that both oxygen and sulfate are reducible compounds 

 and that they serve essentially the same function, as oxidiz- 

 ing agents, in the metabolism of these t^vo types of bacteria. 

 Kluyver also perceived that the chemical reactions catalyzed 

 by bacteria are generally oxidation-reduction processes in 

 which some compounds are oxidized and others are reduced 

 in a series of simple and chemically intelligible steps. His 

 analysis of the available data on hexose decomposition by 

 different bacteria led to the view that in most cases the 

 process consists of a conversion of the sugar to two C3 com- 

 pounds, which in turn are converted to C2 and C^ com- 

 pounds. These various pieces of the hexose molecule are 

 then transformed by oxidation, reduction, and conden- 

 sation reactions to the observed products of catabolism. 

 Our knowledge of bacterial carbohydrate metabolism has 

 greatly expanded in recent years, and numerous changes 

 have been required in this simple picture. Nevertheless, the 

 concept of an underlying unity in biochemistry, first de- 

 veloped in some detail by an analysis of the extensive in- 

 formation on bacterial metabolism, has become a corner- 

 stone of our science. 



The severe limitations of the chemical balance experi- 

 ment method for the study of intermediary metabolism in 

 bacteria were soon recognized, and a search for better 

 methods was stimulated. During the last fwenty years 

 several new or improved methods have been developed 

 which are largely responsible for the current rapid expan- 

 sion of knowledge in this field. 



One of these is the tracer method. Use of the stable and 



