Airway obstruction and collateral ventilation.

Peter T. Macklem, “Airway Obstruction and Collateral Ventilation,” p. 380, paragraph 5, line 1, should read: Above a critical length-diameter ratio of 2−1/2 catenoid formation is impossible; T. J. Biscoe, “Carotid Body: Structure and Function,” p. 449–456. See corrected pages (R449–R456) bound in the front of this issue (October).