In the present part, the author studied the interaction of two substrates to oxidation-reduction potential. Salmonella typhi 57 S was used as the test organism. The results were as follows: 1) The combination of glucose and glutamate, markedly accelerated the fall of potential, while those of glucose and alanine, and glucose and lactate accelerated it moderately. 2) The combinations of aspartate and lactate, glutamate and lactate, malate and glutamate, alanine and malate, and aspartate and alanine did not noticeably accelerate the fall of potential. 3) In the combinations of aspartate and glucose, and lactate and alanine, contrary to the above-mentioned ones, the fall of potential was less than that in each of the substrates. 4) As the cause for the effect of the combinative administration of two substrates, transamination will play a very important role, and the opinion that the hydrogen production by hydrogenlyase is the only cause for the rapid fall of potential, can not be approved as a whole. The essential cause will be, however, disclosed by the studies in future.