84 



PHYSIOLOGY OF BACTERIA 



In B, a little air entered accidentally, causing a low start 

 of the potential ; after about 1 hour, the original potential 

 was again established. Curve C shows the result of 

 vigorous shaking with air; the potential remains low and 

 does not recover. The culture was too old for new 

 growth to occur and those old cells which produced the 

 original potential difference (probably anaerobes) were 

 apparently unable to function. 



In some other experiments, Gillespie measured also 

 the hydrogen ion potential by bubbling hydrogen through 

 the medium. The following values were obtained: 



Table 11. — Hydrogen Electrode and Reduction Electrode 

 Potentials of Various Cultures of Bacteria 



The reduction potentials of the aerobic spore-formers, 

 B. suhtilis, B. mycoides and one unnamed species, are 

 quite low in comparison to the facultative Bad. coli 

 and the putrifying solution containing anaerobes. 



The hydrogen electrode potential is the potential we 

 measure in determining pH, except that it is recorded 

 here in volts. We can also define it as the reduction 

 potential of hydrogen gas at 1 atmosphere of pressure 



