1. The respiration of Amoeba proteus was measured. 10 c. mm. of cells were found to use about 1.6 mm.3 of oxygen per hour at 20°C. The respiratory quotient was found to be nearly unity.
2. No anaerobic metabolism was found for Amoeba.
3. The respiration of Blepharisma was found to be from 3 to 7 mm.3 oxygen per hour for 10 mm.3 cells. The respiratory quotient was about 1.
4. Blepharisma was shown to have a definite anaerobic metabolism. 80 mm.3 cells caused the evolution of 12.5 mm.3 carbon dioxide per hour at 20°C. in the presence of bicarbonate.