1930s, Diagram, N2 Washout, Spirometer Knipping Spirometer, Lung Volume measurements, 1939 May 28, 2013 Richard Johnston Leave a comment From: F. J. C. Herrald and J. McMichael. Determination of Lung Volume: A Simple Constant Volume Modification of Christie’s Method, Proc. R. Soc. Lond. B 1939 126, February 1939