Abstract: A humidifier for pulmonary assistance systems which includes a transparent housing with an air passage extending therethrough and water reservoir. The passage includes a convergent-divergent section separated by a narrow throat. A narrow channel connecting the reservoir to the throat so that with the divergent section being open to the reservoir, the differential pressure between the reservoir and the throat causes water to flow into the air passage. A collection surface is provided in the divergent section for extracting water droplets from the air flowing through the passage, and a heating panel is provided for heating the water in the reservoir.