Studies in the Respiration of Paramecium Caudatum

Abstract

1. A method is described for reducing the numbers of bacteria in a suspension of Paramecium caudatum by an electrically directed migration through a sterile column of liquid. The resulting suspension was suitable for metabolic experiments. 2. Details are given of a Cartesian diver respirometer of ‘macro’ dimensions; this apparatus has a precision of about 10%. 3. The effect of pH on the endogenous respiration of a homogenate of P. caudatum showed an optimum in the region 7.0-7.3, with a wide tolerance on the acid side of the optimum but low tolerance on the alkaline side. 4. The endogenous oxygen consumption had a value of 1.9µl. per 10⁴ animals per hr. and was inhibited 60% by 0.01 M-cyanide and 40% by 0.01 M-azide. Methylene blue did not increase the endogenous oxygen uptake. 5. Succinic acid doubled the oxygen consumption, this increase being inhibited by malonate. Methylene blue increased oxygen consumption in the presence, of succinate still further, and also abolished the inhibition of this extra respiration by cyanide and azide. 6. It is concluded that P. caudatum resembles other animal tissue in possessing an active succinic dehydrogenase.