100 



PHYSIOLOGY OF BACTEKIA 



The kind of the compound determines the potential. 



The quantity of this compound is one of the main 

 factors in determining the rate of reduction. 



The reduction capacity of the system is determined 

 by the sum of the reversibly and the irreversibly oxidiza- 

 ble substances. 



This might be illustrated by an experiment of Dubos 

 (1929) who was the first to emphasize the rate of reduc- 

 tion as an essential factor. He measured the rate of 

 methylene blue reduction by cysteine in vaseline-sealed 

 tubes at 37°C. 



The rate of reduction was determined by the quantity 

 of cysteine, but also by the amount of irreversibly 

 oxidizable organic compounds from broth and yeast 

 extract. 



The meaning of the reduction potential of a bacterial culture is, 

 at the present stage of developments, rather uncertain. If a bac- 

 terium produces a potential lower than the final potential of the 

 oxygen-free medium, it indicates primarily nothing but the presence 

 of a cell product with a lower reduction potential. 



Next comes the question: If the cell forms a compound which 

 creates a potential of —0.100 volts in the medium, must this cell 

 produce within its protoplasm this same or a still lower potential 

 in order to produce such a compound? Must the reduction potential 



