From Johnson RL, Spicer WE, Bishop JM, Forster RE. Pulmonary capillary blood volume, flow and diffusing capacity during exercise. J Appl Physiol 1960; 15: 893-900
“Measurements were made as follows: after exhaling to residual volume, the subject went on the mouthpiece and rapidly inhaled a measured volume of the gas mixture from bag A. This breath was held for a measured time after which is was exhaled rapidly. The first liter of exhalate was allowed to clear the dead space, after which tap A was turned 90 degrees counter clockwise and an alveolar sample of a bout a liter was collected in bag B. t was not convenient to clamp this wide-mouthed sampling bag and remove it; therefore, the sample was aspirated into another removable bag C, in which it was sealed and set aside for later analysis.”