156 RESPIRATION 



oxygen is stored in the blood and tissues, and that for this reason 

 a man who has breathed oxygen for a time has a distinct physio- 

 logical advantage as regards performance of work over a man 

 who has simply breathed air. Douglas and I found 16 that if oxy- 

 gen is breathed quietly before an exertion there is no physiological 

 advantage if the breath is not held. The extra oxygen in the lungs 

 is quickly washed out by the breathing, and there is nothing to 

 indicate the existence of any other extra store of oxygen in the 

 body. If, however, the breathing is forced before the exertion, 

 there is considerable advantage whether air or oxygen is breathed 

 during the forced breathing ; and this advantage is due simply to 

 washing out of CO 2 . As will be shown in Chapter XII, the tis- 

 sues and venous blood cannot become highly saturated with oxy- 

 gen when this gas is simply breathed at ordinary atmospheric 

 pressure; and if oxygen had any appreciable effect apart from 

 that due to the actual presence of an increased percentage of oxy- 

 gen in the lungs the result would be very unintelligible. 



A clear and striking light has been thrown on this subject by 

 some recent experiments by Dr. Henry Briggs. 17 He found that 

 when equal work is done on a Martin's ergometer the percentage 

 of CO 2 in the expired air is, in persons not in good physical train- 

 ing, considerably higher when air rich in oxygen is breathed than 

 when ordinary air is breathed. In persons in the best physical 

 training, on the other hand, there is practically no difference until 

 the work done is very excessive. The following table is from his 



" Douglas and Haldane, Journ. of Physiol., XXXIX, Proc. Physiol. Soc., p. i, 

 1909. 



17 Briggs, Henry Fitness and breathing during exertion, /. Physiology, Vol. 53, 

 1919-1920, Proc. Physiological Soc., p. 38-40. 



