Apparatus for administering pulmonary medication to control the concentration thereof or a fixed volume of air comprising a mouthpiece (19) having one end adapted to communicate with a human oral cavity and a second end communicating with an inflatable envelope (11). The inflatable envelope further includes stays (13) for maintaining the interior surfaces of the envelope apart. A nebulizer (17) is disposed within the mouthpiece having one end terminating in an opening (17a) in the side wall of the mouthpiece for receiving an aerosolized medicant, and the remaining end (18) of the nebulizer is directed towards the inflatable envelope whereby aerosolized medicant is directed into the envelope before being expelled by a negative pressure applied to said mouthpiece through a bidirectional channel (17c) in the nebulizer.