RESPIRATION 



155 



about .8 per cent, if the increased breathing had been due to CO 2 

 alone; while in the case of Priestley (who was in much better 

 physical training than I was) the rise was .44 per cent in place of 

 an expected rise of about .56. I have since then frequently found 

 that my alveolar CO 2 pressure does not rise appreciably with 

 muscular exertion, and falls if the exertion is very great; though 

 in younger men there is almost always a marked rise, as in the 

 experiments on Douglas, mentioned in Chapter II. The absence 

 of a rise in me when ordinary air is breathed is not due to the 

 formation of lactic acid referred to in Chaper VIII. I found in 

 1917, however, that there is a well-marked rise when a little oxy- 

 gen is added to the inspired air. The failure of my alveolar CO 2 

 to rise was therefore due apparently to slight anoxaemia during 

 muscular exertion. 



It has for long been well known to engineers that men perform 

 hard physical work more easily when they are working in com- 

 pressed air. This was very evident, for instance, during the work 

 on the Blackwall tunnel under the Thames, which I visited about 

 25 years ago. At the existing air pressure the alveolar oxygen 

 pressure would have 3^/2 times its normal value. In breathing 

 nearly pure oxygen while wearing a mine rescue apparatus, I 

 share the very common experience, that in spite of the weight of 

 the apparatus, heavy exertion, such as walking very fast, is much 

 easier. On the other hand, even a very moderate increase in alti- 

 tude increases considerably the panting on exertion. 



Some years ago Hill and Flack 15 published a number of ob- 

 servations on the apparent effects of oxygen before and after 

 muscular exertion. Many of their observations were concerned 

 with very striking effects, already referred to, of oxygen in pro- 

 longing the time during which the breath can be held. They 

 showed that this effect is just as marked when exertion is per- 

 formed with the breath held as during rest. They also found that 

 oxygen given during the distress immediately following severe 

 exertion has a distinct effect in raising the blood pressure, improv- 

 ing the pulse, and alleviating the distress. This indicates that a 

 raised partial pressure of oxygen in the alveolar air increases the 

 oxygenation of the blood, and that part of the distress caused by 

 severe muscular work is caused by deficient oxygenation of the 

 arterial blood. I am unable to agree, however, with their further 

 conclusion that when oxygen is breathed a large amount of free 



15 Hill and Flack, Journ. of PhyswL, XXXVIII, Pro. PhyswL Soc,, p. xxviii, 

 1909 ; and XL, p. 347, 1910. 



