In the investigation of the relationship between the accelerative action of Mg(++) and Fe(++) on the O(2)-uptake of Sal. typhi and the time when such metal ions are added, the author obtained the following results: 1. The substrates that accelerate the oxygen consumption of cells in the presence of Mg(++) or Fe(++) are glucose, lactate, pvruvate, and acetate. 2. When metal ion is added prior to a substrate and the substrate is added 20 minutes, 40 minutes, 60 minuter or 120 minutes later, the O(2)-uptake curve makes an upward curvature along with the lapse of time. 3. In the case where a substrate is added before metal ion, the accelerative action on O(2) uptake is weakened in proportion to the length of delay in the metal ion addition. By studying the relationship of the mutual actions of two substrates variously coupled from several substances with the time of adding such a combination of substrates in O(2)-consumption of Sat. typhi, the author obtained the following results: 1. It has been found that there are three sets of cases; namely when two substrates are added simultaneously, the amount of O(2)-uptake is greater than the total O(2)-uptake of two individual substrates (acceleration); O(2)-uptake is about the same as the total of two substrates measured separately; and the amount of O(2)-uptake becomes less than the O(2)-uptake of single one of the two substrates (inhibition). 2. Looking over the relationship of the adding time of two substrates as to accelerate O(2)-uptake and the accelerative effect, there are two different sets; namely, the one where one substrate is added later than the other, the accelerative effect is greater; and on the contrary the other where such an effect is diminished. This phenomenon seems to be due to the gradings in the oxidation (combining with oxygen) of each substrate by cells.