A complete unit for comprising rates of absorption or revolution of gases by small organisms, during respiration. The apparatus consists of two stoppered boiling tube connected by three way taps to either limb of a graduated manometer. One tube holds the organism and has a syringe for altering the level of liquid in the manometer during setting up. The other tube acts as a control thermo-barometer. CO2 given off by the respiring organism is absorbed by potassium hydroxide in the experimental chamber resulting in a change in the level of liquid in the manometer tube. Complete with wire baskets for supporting organisms.