READJUSTMENTS OF REGULATION 59 
tion, just as I was in the case of CO poisoning. On 
rereading Glaisher’s account of his balloon expe- 
riences I was much interested to see that though he did 
not clearly understand the cause of mountain sickness 
he was quite convinced that repeated ascents produced 
acclimatisation. I have recently found that the effects 
of acclimatisation can easily be observed at ordinary 
atmospheric pressure in a closed chamber in which the 
oxygen percentage has been greatly reduced. An 
acclimatised person remains of a normal colour, and 
has no unpleasant symptoms, while an unacclimatised 
person soon becomes blue in the face, and may faint. 
In acclimatisation to high altitudes there are evi- 
dently three factors—the increased activity of the 
lung epithelium in absorbing oxygen, the increased 
breathing, and the increased percentage of haemo- 
globin. Of these the last raises the oxygen pressure 
in the capillaries of the body, the second diminishes 
the fall in alveolar oxygen pressure, and the first 
raises the arterial oxygen pressure much above the 
alveolar oxygen pressure, whereas at sea level the 
arterial oxygen pressure is no higher, as a rule, than 
the alveolar oxygen pressure. The teleological sig- 
nificance of these changes seems clear, and a vitalist 
would naturally point to this as evidence of the inter- 
ference of the vital principle. But we must analyse 
the facts further. 
