58 ORGANISM AND ENVIRONMENT 
striking results than in the later experiments of Doug- 
las and myself. The earlier experiments were very 
long ones, and we were frequently exposing ourselves 
to oxygen want for many hours at a time. We had 
probably thus both become more or less acclimatised, 
so that our lung epithelium reacted very promptly to 
the slight oxygen want produced by the CO. In no 
other way can I explain the fact that we were able to 
breathe with complete impunity percentages of carbon 
monoxide which in subsequent isolated experiments 
were found to produce severe symptoms. The same 
criticism applies to my own early experiments as to 
the effects of definite percentages of CO. I was 
breathing CO every day often for hours, and doubt- 
less had become highly acclimatised to want of oxy- 
gen, so that I underestimated the effects of CO on 
ordinary unacclimatised persons. 
The part played by the lung epithelium in acclimati- 
sation to want of oxygen makes it possible to under- 
stand how mountaineers have succeeded in reaching 
such great heights as they have. In his recent explora- 
tions in the Himalayas the Duke of the Abruzzi 
reached the height of 24,600 feet, the barometric pres- 
sure being only 312 mm. An unacclimatised person at 
this pressure is rapidly disabled completely; but the 
Duke’s party did not suffer at all from mountain si¢k- 
ness or other serious physiological inconvenience. 
Dr. Filippi, a member of the expedition, in his account 
of it expresses the opinion that there is no such thing 
as mountain sickness due to rarefaction of the air. He 
was entirely deceived by the influence of acclimatisa- 
