My 1954 John Deere 40T utilizes a oil bath air cleaner setup. In trying to explain it to my brother I realized I didn’t fully understand it myself. So I did some research. Here is a site that explains it wonderfully well: http://vintagetractorengineer.com/2009/01/oil-bath-air-cleaners-for-tractors/
The short of it is that the cup at the bottom is full of oil and air has to go through the oil. The air passes through but the dirt and dust get stuck in the oil and settle to the bottom. My tractor also utilizes a sediment bowl in the gas line as opposed to a fuel filter. I guess back in 1954 they didn’t like expendable parts, just expendable fluids.