are fed into the incubator per minute prior art oxygen concentrators 12 based on pressure swing adsorption deliver about 6 l per minute at 95 oxygen concentration and a desired maximum oxygen concentration of about 38 is thus obtained in the case of a fresh air flow 13 of about 20 l of ambient air per minute in the case of a total fresh gas flow 3 of 26 l per minute into the interior space of the incubator the inflow of the fresh air flow 13 is achieved by means of the fan 10 and set to a constant value of about 20 l per minute by the flow resistance of the inlet line and the sterilizing filter 11 the fan may be designed as a rotary compressor as described in u s pat no 6 418 917 or a radial compressor as described in u s pat no 6 474 960 both of which are incorporated herein by reference the fresh gas flow 3 is monitored e g on the basis of the electric data of the blower 10 namely the current the voltage and the speed so that an increased resistance of the sterilizing filter 11 can also be recognized hereby the oxygen concentration is controlled after the measurement of the current oxygen concentration in the interior space of the incubator by means of the oxygen sensor 5 which has preferably an electrochemical measuring cell the measured.