 Briefly, a series of stopcocks is configured to allow perfusion of the above solutions through the port at the tip of an exploring catheter PE50 tubing. All test solutions are perfused at a rate of 5.0 cc per minute. In each nostril, the PD readings in Ringers at 0.5, 1.0, 1.5, 2, and 3 cm lumen negative are averaged and taken as the average baseline PD. The catheter tip is then placed at the most negative PD site and maintained for superperfusion measurements with a small piece of tape applied to the nasal tip to hold the catheter for the duration of the protocol. All solutions are warmed to 37 C prior to contact with the nasal mucosa. 