1. Quiescent sciatic nerve of the frog discharges CO2 at the average rate of 0.00876 mg. CO2 per gram of nerve per minute. 2. Sciatic nerve steeped one minute in boiling water discharges CO2 at first at a low rate and after an hour and a half not at all. 3. Degenerated sciatic nerve discharges CO2 at a slightly higher rate than normal living nerve does. 4. Connective tissue from the frog discharges CO2 at an average rate of 0.0097 mg. per gram of tissue per minute. 5. Assuming that a nerve is composed of from one-half to one-quarter connective tissue the CO2 output from its strictly nervous components is estimated to be at a rate of 0.008 mg. CO2 per gram of nerve per minute. 6. Stimulated sciatic nerve increases the rate of its CO2 output over quiescent nerve by about 14 per cent. When this number is corrected for strictly nervous tissue the rate is about 16 per cent. 7. The increased rate of CO2 production noted on stimulation in normal sciatic nerves was not observed when they were boiled, blocked, or degenerated. It was also not observed with stimulated strands of connective tissue.