Abstract: To permit accurate introduction of aerosols containing, for example, irritants or similar substances, into the pulmonary tract or airways of a patient, the breathing cycles of the patient are counted and, after a number of normal breathing cycles, and during a limited period of time in the inhalation phase of a breathing cycle, and after commencement of the inhalation phase, a predetermined quantity of aerosols is introduced to the patient by applying compressed air of controlled pressure to an atomizer or aerosol fog generator (32, 34); initiation of inhalation is sensed, for example by a pressure transducer (24), the output of which is connected to a threshold stage (50) sensing inhalation and exhalation, respectively, and setting a time delay period for example of less than half than normal duration of the inhalation phase of the patient, which then triggers a timing interval by a monostable flip-flop (56) which, during the time period thereof, applies the controlled compressed air to the atomizer (32, 34)