168 OXIDATION-REDUCTION POTENTIALS 



than is to be found in even the simplest unicellular organisms. In the matter also of 

 keeping conditions constant during an experiment, faint hope can be entertained by 

 the biochemist, for hving imphes constant changing ; directly the dynamic state gives 

 place to the static, we have not life but death, or, at least, a moribund state of 

 suspended animation. 



In studying the electrode potentials of biological systems, therefore, there are 

 great difficulties, (1) in obtaining reproducible results, since no two organisms can 

 be absolutely identical, and no organism can be quite the same on two different 

 occasions ; (2) in knowing what constituents of the system are responsible for the 

 potential changes observed, and (3) in realising the effects of components of the 

 system which do not directly affect the potential, but which do so indirectly by 

 catalytic, poising or other activities. In the presence of appropriate cellular enzyme 

 functions reversible oxidation-reduction processes occur which are unknown in 

 their absence. Other oxidation-reduction systems which are irreversible or only 

 semi-reversible affect the equilibria of reversible systems and complicate the results. 

 In view of these difficulties, it is not surprising that many problems remain unsolved, 

 but they need not be regarded as insuperable obstructions to progress. Even in the 

 short history of the subject numbers of successful circumnavigations round the 

 obstacles are already reported. 



Interesting facts emerge from a study of the changes in oxidation-reduction 

 conditions produced by bacteria in the medium by which they are surrounded. 



The metabolic activities of bacteria and their obtaining energy by oxidation 

 of nutrient material result in a general development of reducing conditions in their 

 cultures. Conclusions of considerable interest and of practical importance in the 

 use of culture media are resulting from studies of the electrode potentials developed 

 in bacterial cultures growing under conditions as nearly as possible identical with 

 those used in bacteriological laboratories. It is evident that the conditions required 

 for the manifestation of their characteristic properties must be the conditions chosen 

 also for the study of electrode potentials if any correlation of the different bacterial 

 activities is to be attempted. 



The reducing conditions established in bacterial cultures during the logarithmic 

 phase of growth vary from organism to organism. Different ranges of reducing 

 effect may be seen ; for example, the aerobes in general are able to reduce ordinary 

 aerobic culture media until a moderately intense reducing level is reached, but 

 many are unable to effect further reductions. The anaerobes, on the other hand, 

 are unable to effect any reduction in ordinary aerobic cultures, but if the medium 

 is partially reduced to begin with, e.g., by exclusion of the oxidising effect of air, 

 they are able to establish and maintain quite intense reducing conditions. 



Anaerobiosis like other properties of bacteria can be traced to the metabolic 

 pattern of the organism and depends upon the enzyme systems that can be called 

 into play. Being capable of adaptation and mutation with comparative ease the syn- 

 thetic and catabolic functions of a strain of bacteria are susceptible to very wide 

 variations, some of which are direct and fairly rapid adjustments to the environment 

 and others only produced by considerable alteration to the " genes " or their nucleic 

 acids. 



