Further experiments on the respiration were made, in which consumptions of oxygen by three species of root nodule bacteria and their respiratory quotients in a buffer solution were concerned under an atmosphere containing different quantities of oxygen, and also two species 5 of the bacteria in the yeast water mannitol solution under that containing 20 per cent oxygen, varying percentages of CO_2,and sufficient nitrogen to make one atmosphere. Oxygen consumed by Rh. trifolii under PO_2 lower than that of ordinary air (20 per cent) was repressed, whereas that by Rh. meliloti as well as Rh. lupini was not. With regard to respiratory quotients, data obtained with Rh. trifolii was larger than with the others, but must be below carbohydrate level under consideration of no aerobie glycolysis. It was suggestible that an atmosphere containing quantities of CO_2 greater than 0.05 per cent would initiate the respiration process of Rh. trifolii on the whole.