Abstract: The device for feeding gaseous substances into liquid media comprises a number of hollow membrane bodies which are permeable to gas and contain the liquid media. These membranes are arranged with a distance between them in such a way that they can be reached by the gaseous substances. Such a device lends itself particularly to air purification. Gaseous substances such as nitrogen oxides can be converted with the aid of this device. According to the invention the device can also be used for pure or mixed cultures of various microorganisms whereby, above all, information about the toxicity of individual substances can be obtained.