Some special respiratory effects of CO2 in pigeons.

Injections of CO2-gas have been made into an abdominal air-sac of pigeons. The resulting alterations of respiratory rate and of breathing efforts are dose-dependent and easily reproducible. The receptive zones for these effects do not seem to be located in the air-way system itself; they may be in the respiratory center. Some data provide further evidence for the assumption that the ventilation of the abdominal air-sacs is mainly one-directional, from outside to gas-exchange compartments. Panting increases the ventilation of the abdominal air-sacs.