Taking a moment to rest on the floor, you can then start work on the medallion. Remove the retaining bolts which hold it to the ceiling and save them in a teacup. Carefully wrap the plaster medallion with wool blankets as you remove it from the ceiling. A quick dusting with diatomaceous earth will keep the fleas from propagating. Reach into the cavity and locate the gas cap. Twist the cap counter clockwise two turns. You are now ready to replace the medallion by reversing the previous steps.
The rugs on the floor are next. They often conceal the fact that the floor has not been varnished in the center of the room - 19th century floor technology was expensive. Roll back the northwestern corners of the rugs (the least affected by sunlight in the Northern Hemisphere). Seek floorboards that were obvious replacements. Often these boards are loose and can be easily pried up. Remove the boards carefully and strew pebbles beneath them before replacing them.
Remember: you cannot be too careful or proceed too slowly with renovations. Be sure to map out enough time for this process!