48 ORGANISM AND ENVIRONMENT 
be found that the alveolar CO, 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 CO, 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- 
Alveolar 
Gas 
eg. 
150 
440 Wy aglotei 
% 
130 180 
120 170 
0 
ne i jatar 16! 
100 ra 150 
90 ~ at >t — 140 
poke eed 
80 =X cai - 130 
7 
ater 
70 bet T+ Lact 120 
4a 
60 . | xe TT) 
ry yl 
50 | Lat ‘s z 100 
40 Br call “ aN 90 
rm aS 
30 a PES al 30 
a ee a roo Mery ss 
20 ==} f= = 70 
Womeb. ~~ ee ~3a 
10 60 
0 ato) +f at pt at fl gg 4 50 
Mones Fyeas. 800 750 700 650 600 3530 900 430 400 $80 300 250 £00 
| 
Mlitode in fo 0 2000 4000 000 S000 10000 Iko00 16000 20000 26000 
Fic. 3. Alveolar pressures of oxygen and COz 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 450 mm. of mercury. 
