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During the course of certain experiments on the mechanism of pulmonary ventilation during large breaths it was noted that the amount of oxygen absorbed was unexpectedly large. It was decided to investigate this phenomenon in detail. METHODSDeternuirations, as far as possible, were done in the early afternoon. The subject (G.H.A.) rested in the position in which the subsequent experiment was to be performed (i.e. either sitting upright or lying flat) for 10 min. The rate of oxygen uptake was then determined by spirometer or Douglas bag; and 5 min. later the experiment was performed. (In that interval, especial care was taken that the subject should refrain from activity calculated to alter the respiratory rhythm.)An experiment involved the collection of 1-S vital capacity breaths in a Douglas bag, previously rinsed with expired air. An end expiration sample of the last breath prior to collection was taken and a similar final sample taken at the end of the last collected expiration. The time between the specimens was recorded. A 101. Douglas bag was used where possible, otherwise one of standard size. The bag was fitted with a two-way tap-opened and closed by the subject between breathsconnected to a short wide mouthpiece. Although the manipulation of the tap between each breath involved the possibility of a slight loss of expired air, this was preferred to the risk of altering the results by using a valve with its inevitable slight resistance. The bag was sampled and emptied through a wet meter. Allowance has to be made for the higher oxygen contact of the alveolar air at the end of the large breaths; this accounts for a substantial proportion of the oxygen uptake during the time of the experiment.

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