From: The respiratory response to carbon dioxide. By HW Davies, GR Brow, CAL Binger. Journal of Experimental Medicine, 1925, page 38.
“The effect of gradually increasing percentages of carbon dioxide was studied by means of rebreathing in a closed circuit consisting of a modified Douglas Bag with inflow and outflow tubes, a dry meter, and a rubber mouthpiece fitted with inspiratory and expiratory valves. The general arrangement of the apparatus is shown semidiagrammatically in text-fig. 1. The direction of airflow is indicated by means of arrows. A is the modified Douglas Bag of 100 liters capacity. B, B’ are wide bored three-way taps. C is the mouthpiece. D is a twenty-light capacity “B-type” dry meter manufactured by D. MacDonald and company of Albany. The resistance of this meter is almost negligible even at the maximal rates of pulmonary ventilation produced by high percentages of carbon dioxide in the inspired air. E is a small bore side tube connected with an oxygen tank fitted with reducing valve and a flow meter calibrated with approximate accuracy rates of flow of less than 1 liter per minute. A similar side tube, F, is used to obtain samples of inspired air, either into exhausted sampling tubes or directly into the burette of the Haldane gas analysis apparatus. By way of the three-way stop cocks B,B’ the subject may be made to inhale from and exhale into the room air through the meter, and his normal respiratory rate and minute volume may be determined. When the stop-cocks are turned the apparatus becomes a closed circuit, inspiration and expiration being from and to the Douglas Bag, A.”