66 Physiological Effects of Low Atmospheric Pressures. 



(6) After acclimatisation the alveolar carbon dioxide pressure was 

 diminished from about 40 mm. to about 27 mm. during rest or moderate 

 exertion, which corresponded to an increase of about 50 per cent, in the 

 ventilation of the lung alveoli. During severe exertion the alveolar carbon 

 dioxide pressure was about half what it normally is during similar exertion, 

 which corresponded to an increase of about 100 per cent, in the hyperpnoea ; 

 and owing to a temporary alteration in the respiratory quotient the 

 breathing was still further increased. 



(7) The change in the level of alveolar carbon dioxide pressure occurred 

 gradually after going up, and disappeared gradually on coming down, the 

 change taking a number of days to reach completion. 



(8) The percentage of haemoglobin in the blood increased for several 

 weeks on the summit of Pike's Peak, and varied in different acclimatised 

 persons from 115 to 154 per cent, on the scale of the Gowers-Haldane 

 haemoglobinometer, corresponding to an oxygen capacity of from 21 to 

 28*5 c.c. of oxygen per 100 c.c. of blood. The number of red corpuscles per 

 cubic millimetre of blood increased parallel with the haemoglobin, and the 

 percentage volume of red corpuscles, as determined by the haematocrit, also 

 increased in proportion to the percentage of haemoglobin. 



(9) A large increase in the total amount of haemoglobin (determined by 

 the carbon monoxide method) in the body occurred during the first three 

 weeks, and along with this increase there was found, except in the first 

 week, a slight increase in blood volume, as well as the increase, already 

 referred to, in the percentage of haemoglobin. 



(10) On coming down from Pike's Peak the haemoglobin percentage 

 diminished much more rapidly than the total haemoglobin, so that the blood- 

 volume was still further increased at first. It required about four weeks for 

 the excess of haemoglobin and blood-volume to disappear, though the haemo- 

 globin percentage fell to normal much earlier. 



(11) So far as we could ascertain, there was very little change in the rate 

 of circulation on Pike's Peak after acclimatisation. Pulse and blood-pressure 

 were but little affected. In most cases, however, there was a slight increase 

 in the pulse rate. 



(12) After acclimatisation the oxygen pressure in the arterial blood 

 (measured by the carbon monoxide method) rose during rest to about 35 mm. 

 of mercury above the alveolar oxygen pressure (66 per cent, higher), and 

 remained at a level of only about 12 mm. below the normal oxygen pressure at 

 sea-level. Immediately after ascending the Peak and before acclimatisation 

 had occurred, the arterial oxygen pressure was found to be about 45 mm. below 

 normal, and only slightly above the alveolar oxygen pressure. This change 



