Demonstration without instruments of "first gas into the lung is last gas out".
D005459:Fluorides; D005740:Gases / Q000502:physiology*; D006371:Helium / Q000502:physiology*; D006801:Humans; D008168:Lung / Q000502:physiology*; D012129:Respiratory Function Tests; D013455:Sulfur; D014831:Voice
D005740:Gases; D006371:Helium; D013455:Sulfur; D005459:Fluorides