230 



RESPIRATION 



ranged that the incoming air current is directed to the bottom of 

 the bottle, while the subject inhales air from the top. The arrows 

 indicate the direction of the air current caused by the subject's 

 respiration in the main circuit. Two side pipes lead into the rubber 

 pipe connecting D with E. One of these, G, is of large bore and 



Figure 67. 

 Apparatus for determining the arterial oxygen pressure in man. 



short, and is connected with a vulcanized rubber gas bag of con- 

 siderable size, such as is utilized on Clover's ether apparatus. 

 This bag serves only to accommodate each expiration, as the rest 

 of the apparatus is indistensible, and at the end of inspiration 

 the bag collapses entirely. The other side pipe F serves for the 

 admission of oxygen. The oxygen supply is so arranged that oxy- 

 gen enters the main air circuit automatically to fill up the defi- 

 ciency caused by the absorption of oxygen by the subject at each 

 breath. It is essential in a closed system of small size that the 

 oxygen supplied shall be pure; the small amount of nitrogen 

 contained in ordinary cylinder oxygen renders its use inadmis- 

 sible. We therefore in all the later experiments used oxygen 

 made by the action of water on "oxylith" in the generator H. The 

 current of oxygen is controlled by the tap at the top of the gen- 

 erator, and passes along a pipe past a blow-off valve to air J, 

 through a small gas meter K and thence through a water valve 

 M to enter the main air circuit at F. The height of the water above 

 the orifice of the pipe in M is about 2 mm. greater than in J, and 

 the oxygen therefore passes out to air through the valve J unless 



