124 



OXIDATION-REDUCTION POTENTIALS 



Staphylococcus aureus. — ^In general behaviour this organism resembles 

 C. diphiheriw. The organisms display considerable catalase activity and do not 

 form peroxide, and the electrode potentials of cultures remain at a low level after 

 growth (Hewitt, 1930, 1931 ; Clifton, 1933). 



B. dysenterice {Shiga). — Although deficient in catalase, these organisms behave 

 in a manner resembling that of bacteria containing catalase, possibly on account 

 of peroxidase activity (Hewitt, 1931.) The organisms possess rather feeble reducing 

 powers, and even these are inhibited in the presence of bacteriophage. 



Escherichia coli. — The electrode potentials in Escherichia coli cultures reach a 

 very low level, as would be expected from the intense enzymic activity displayed 

 {see fig. 35.) Hydrogen is liberated from cultures, so that the low potentials of the 

 hydrogen electrode are reached, or even surpassed, especially in cultures containing 

 glucose (Gillespie, 1920 ; Cannan, Cohen and Clark, 1926 ; Aubel and Genevois, 

 1927; Hewitt, 1931 ; Boyd and Reed, 1931 ; Clifton, Cleary and Beard, 1934). 

 Clifton, Cleary and Beard (1934) followed the ferricyanide reducing powers of B. coli 

 cultures at different stages of growth, the results being as follows : — 



TABLE 23 



The intense reducing acti\^ty of the bacteria may be gauged from the fact that 

 fifteen million molecules of oxidant may be reduced by one cell in a minute. 



Salmo7iella group. 



In B. typhosus cultures a potential of —0-145 v. was reached (Coulter and 

 Isaacs, 1929). Lepper and Martin (1930) examined meat broth cultures of B. para- 

 typhosus A and B, and found that the potential fell to a much lower level with 

 B. paratyphosus A, possibly associated with the concomitant gas formation. 



Burrows and Jordan (1935) have examined various members of the Salmonella 

 group, and have concluded that each species produces in cultures an electrode 

 potential characteristic of that species. In the next table (table 24) are summarised 

 their results, the mean value of the potentials reached by a number of strains of 

 each species after different incubation periods being given. 



