Category Archives: Douglas Bag

Gas Collection System, 1933


From: Solandt OM, Ridout JH.  The duration of the recovery period following strenuous muscular exercise.  Proceedings of the Royal Society of London, 1933: 113: 327-344, page 329.

“As shown in the diagram, the air expired by the subject is first collected in the 10-liter spirometer. From the spirometer it is pumped through a cooling coil, through the meter, and then into a Douglas bag.  In this way the air is metered before entering the bag, and the bag is only used to collect the air so that a sample may be taken.

“The valves used were of the conventional type, consisting of a circular rubber flap, seating on a metal ring. They were tested before each experiment. The pump used was of the movable blade rotary type and was driven by an electric motor. The meter used was a Sargent wet test gas meter. This type of meter is very sensitive to changes in water level, as Krogh (1929) has pointed out, hence the water level was checked before each experiment. The correct water level was determined by checking the meter against a small Bohr meter which has been calibrated by displacement of air. The accuracy of the Sargent meter was guaranteed by the makers to within 1 percent at rates of flow up to 50 cubic feet per hour.  During the experiments the rate of metering was never allowed to exceed this value. The cooling coil was used to prevent too great a rise in meter temperature owing to the passage of warm expired air through the meter. The effectiveness of this device is shown by the fact that the meter temperature seldom changed as much as one degree during an experiment (2 to 3 hours). By cooling the air, complete saturation with water vapor was also ensured.”

Douglas Bag, Rebreathing system for CO2 response, 1925


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.”

Douglas Bag, 1916


From: The respiratory exchange of animals and man by August Krogh, 1916, page 42.

“Regnard [1879] collected the expired air in a rubber bag from which it was afterwards delivered and measured through a meter, but his bags were probably not tight against diffusion and his technique very faulty.  This principal, however, is excellent for certain types of experiments, and it has recently been revived by Douglas who has worked out a method which is specially adapted for the study of the respiratory exchange during open-air exercise in circumstances where all other instruments would fail, but which also prove useful in a number of other cases, e.g. on bed-ridden patients (Fig. 17). The subject breathes during an introductory period through the mouthpiece and valves.  When it is desired to make an experiment the three-way tap is turned so as to connect with the bag and the expired air collected over a certain period.  With violent exercise a bag taking 60 liters will not hold the air expired during one minute, but is has been shown (Krogh [1913]) that experiments of even shorter duration are sufficient to give perfectly reliable results. The air collected in the bag is afterwards analysed and measured by connecting with a gas meter of suitable size and pressing the air slowly out of the bag. When a gas analysis is considered a thing to be avoided the contents of the bag can be taken through a Haldane set of vessels for absorbing water vapour and carbon dioxide and the total carbon dioxide determined by weighing.”

Douglas Bag, 1920


From: The Newer Methods of Blood and Urine Chemistry, by  By Rutherford Birchard Hayes Gradwohl, Abraham Jacob Blaivas, 1920, Page 373.

“The Douglas Bag.  The Douglas Bag is made of rubber-lined cloth, and is capable of holding from 50 to 100 liters.  It is especially useful for investigations during exercise, since it is fitted with straps so that the bag can be fastened to the shoulders (Fig. 73).  It is then connected with the valves, the mouthpiece of which is placed between the lips.  Respirations are commenced with the three-way valve turned so as to allow the expirations to pass directly outside.  After respiratory equilibrium is established, the three-way valve is turned during an inspiratory period so that the succeeding expirations may pass into the bag.  The time required to fill the bag comfortably is determined with a stop-watch.  The air which has been collected in the bag during the period is thoroughly mixed and passed through a meter, the temperature and barometric pressure are noted, and a sample analyzed in the Haldane gas apparatus.  The bag should be emptied completely by rolling it up when nearly empty.”