DOUGLAS METHOD. 69 



in 100 c.c. gas samplers, the analyses being made with the laboratory 

 form of the Haldane gas-analysis apparatus. 1 



In connection with this series of experiments two types of valves 

 were used (figs. 29 and 30), both manufactured by Siebe, Gorman and 

 Co., Ltd., of London, England, and used by them in their mine-rescue 

 apparatus. The form shown in figure 29 consists of a metal tube, 

 20 mm. in diameter, with an enlargement at B. Across the opening 

 of this enlargement, a thin mica disk (C) rests upon a very narrow 

 metallic edge. When air enters at A, this disk is raised, the upward 

 movement being limited by the cross-wires above the disk. When the 

 air presses against the top of the disk, the mica flap falls again into 

 place, so that no air can pass back through the opening A; the gene- 

 ral direction of the air is thus from A to E. The valve may be taken 

 apart by unscrewing at F. A pair of these valves is used in separating 

 inspired and expired air. 



FIG. 30. Rubber-flap valve used with the Douglas method. 



The cross-section A shows the general construction, and B the openings of the valve. A rubber 

 flap connected at d opens and closes, the position when closed being indicated by b b, and when 

 open by c c. The direction of the air-current is from e to /. ' 



The other form of valve is shown in figure 30, the cross-section being 

 designated A and the face of the opening through the valve B. This 

 valve is essentially a metal tube, with a concave disk across its bore, 

 in which there are a number of openings; a rubber flap covers the 

 openings in the disk. When the valve is used as an inspiratory valve 

 this flap opens and closes as the subject inspires and expires. The 

 size and arrangement of the openings are shown in B, while A shows 

 the disk with the openings in cross-section at a, a. The position of 

 the rubber flap when closed against the openings is indicated by b, b 

 in A, and when open by the dotted lines c, c. The rubber flap, which 

 is circular in shape, is held in place by a knob, d, over which it is 

 slipped. The direction of the air in passing through the valve is from 

 e to /. The parts of the valve may be separated by unscrewing it at g. 



In the experiments carried out by the Douglas method, the pneu- 

 matic nosepieces shown in figure 4 and the Tissot valves shown in 

 figure 23 were also used, but this did not produce any alterations in 

 the general principle of the method. 



'See p. 71. 



