From Forster RE, Fowler WDS, Bates DV, Van Lingen B. The absorption of carbon monoxide by the lungs during breathholding. J Clin Invest 1954; 33: 1135-1145
“Inspiration was made from a neoprene bag (A) contained in a sealed metal chamber (B). Expiration was made through the flowmeter (C) into chamber (B). A 6-liter spirometer (D) recorded changes of total volume in the system. Two 2 cm. diameter three-way taps (E and F) were provided. Tap E enabled the subject to breath out the first liter of an expiration into the circuit, and to collect the remainder in a rubber bag (G) close to the mouthpiece. Tap F permitted closure of the inspiratory bag to prevent loss of the inspired gas. The inlet (H) to the mass spectrometer sampling tube was at the mouthpiece.”