48 



ORGANISM AND ENVIRONMENT 



be found that the alveolar COg 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 CO2 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- 



fflt*elar 

 150 



MriHn -Pfn^&OO 150 100 6iO 60O SSO 900 MSO fiOO 3S0 300 260 SOO 

 ^m/y. I I i I I t I I I I 



fiiUvikinfi, 000 4000 COSO 8000 10000 (4000 (6000 0000 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. 



