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), the compressed air being shut off, and thus terminating atomization well in advance of the end of the inhalation cycle, and preferably less than 1/2 second, for example less than 0.3 second, so that the quantity of aerosols is accurately controlled and will reach the alveoli to be absorbed in the lungs so that the breathing tube will be essentially free from contaminating aerosols.