A composite polarizer including a first polarizer having a plurality of parallel metal vanes and a second polarizer having a plurality of parallel layers of dielectric material is provided. The cleaning appliance has a suction-removal apparatus for removing damp air from the cleaning chamber by suction, and at least one heat recovery device. There is obtained a recycle gas to which fresh synthesis gas is admixed, the recycle gas being recirculated to the reactor as synthesis gas. Another desired path is selected with the selectively steerable distal portion and the endoscope body is advanced again.