Air in the tubes.
D000393:Air Pollutants / Q000032:analysis; D001249:Asthma / Q000209:etiology*; D002648:Child; D004391:Dust / Q000032:analysis; D006801:Humans; D008131:London; D008855:Microscopy, Electron, Scanning; D011890:Railroads; D012867:Skin / Q000032:analysis
D000393:Air Pollutants; D004391:Dust