170 OXIDATION-REDUCTION POTENTIALS 



potential no reduced SH groups are present. Wilson (1930) found that variations in 

 virulence and colony form of B. aertrycke accompany alterations in the oxygen 

 content of the gaseous environment of cultures. 



The ripening of cheddar cheese without the occurrence of deleterious faults 

 is apparently dependent upon the development on the correct series of electrode 

 potentials at different stages Beer is said not to keep and tissue cultures not to 

 proliferate at inappropriate electrode potentials. Milk is tested by the use of oxida- 

 tion-reduction potential dyes. So that in the practical applications of biochemistry 

 and bacteriology, as well as in the laboratory, electrode potentials have assumed 

 prominence. 



Potter (1911) observed the potential difference between a culture medium 

 inoculated with bacteria and a sterile control, but Cohen (1931) has carried the 

 matter to an extreme point. He has built up a bacterial battery by connecting in 

 series a number of cells each composed of 10 c.c. of culture coupled to a sterile control. 

 The culture medium contains a poising agent such as potassium ferricyanide or 

 benzoquinone. Each unit " yields about 0-2 ma. at a pressure of 0-5 volt with very 

 small polarisation for at least 5 minutes. By this means we have been able to build 

 up a bacterial battery furnishing current of about 2 ma. at a pressure of 35 volts."' 



" The human body at rest uses about the same amount of energy as a 100-watt 

 electric light bulb. Like the bulb, the body obtains this energy by a process which 

 involves the flow of an electric current. In the living cell, electrons flow from the 

 foodstuffs we ingest to oxygen, thus reducing the oxygen to form water. The 

 ' filament ' of the cell over which these electrons flow is not of uniform composition 

 as is a light bulb. The electrons in the cell are passed along over a chain of 

 compounds composed of iron-containing proteins, the cyt.ochromes, and vitamin- 

 containing units named coenzymes. The over-all j^rocess involves a potential 

 change of about 1-17 v. and a total flow of current in all the body cells which 

 amounts to about 76 amps. The process occurs, however, in a stepwise fashion 

 which involves five or six successive transfers of electrons between the various 

 components comprising the cellular ' filament ' or oxidative chain. Each pair of 

 components may thus be looked upon as forming a battery, the pairs being 

 connected in series. A drop in voltage occurs with the interaction of each pair in 

 this series ; its magnitude may be estimated from our knowledge of the oxidation- 

 reduction potentials c>f each of the systems involved. How the energy is utilised 

 by the cell is not exactly known. A good portion of it, however, seems to be 

 converted into high-energy phosphate bonds which, in turn, directly supply the- 

 driving force for many of the various physiological processes which constitute 

 life." (Ball, 1947.) 



The intense reducing activity of bacteria, associated necessarily with their 

 metabolic functions, is illustrated in a calculation by which it is shown that during the 

 active logarithmic phase of growth a single cell of B. coli can reduce fifteen million 

 molecules of oxidant each minute. The transport problem alone, of bringing millions- 

 of molecules up to the cell surface and removing them after reduction, must be 

 considerable. 



Developments in chemotherapy and the rapid advances in the use of antibiotics 

 stimulated by the work of Fleming and Florey raise questions which impinge upon the 



