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A TEXTBOOK OF PHYSIOLOGY 



Expired air is diminished about one-fiftieth in volume as com- 

 pared with the inspired air. This is due to the oxygen combined 

 with products of tissue oxidation which passes out of the body in 

 the urine. To obtain expired air for analysis, the subject breathes 



I 



FIG. 151. HALDANE'S GAS ANALYSIS APPARATUS. 



through a mouth-piece, provided with inlet and outlet valves, into 

 a large rubber-lined canvas bag. The contents of the bag are 

 squeezed through a meter, and thus the volume of expired air 

 measured ; while a sample is secured for analysis by means of a T -piece 

 into an evacuated sampling tube. If the subject breathe for, say, 





