48 



ORGANISM AND ENVIRONMENT 



be found that the alveolar C0 2 pressure has fallen, 

 which shows that the breathing is deeper. This fall 

 reaches a certain amount, depending on the altitude, 

 and then ceases. On the subject's return to sea level 

 the alveolar C0 2 pressure does not at once return to 

 normal again, but may take many days, or even some 

 weeks, to do so. Figure 3 shows graphically the aver- 



Hhtolar 



O 



fltn**T+*a»S°0 150 TOO 650 600 350 000 430 400 3S0 300 SSO ZOO 

 — **K || | III III I 



fiHX»<k in fi, 2000 4000 6000 8000 M000 14000 16000 20000 26000 



Fig. 3. Alveolar pressures of oxygen and CO2 and per- 

 centages of haemoglobin in the blood of persons ac- 

 climatised to altitudes from sea level to 14,000 feet, — 

 barometric pressures from 760 to 45 mm. of mercury. 



