RESPIRATION 



373 



to 520 mm., corresponding to a height of 1 1,000 feet; but after a 

 few hours they became so seriously affected by mountain sickness, 

 with alarming cyanosis, intolerable headache, and feelings of 

 asphyxia during the night, that they had to raise the pressure to 

 584 mm. (about 7,000 feet). Those ascending Pike's Peak started 

 from a height of about 6,000 feet and were thus partially acclima- 

 tized ; otherwise their symptoms would doubtless have been more 

 marked than they actually were. 



In Chapter IX the quantitative evidence has already been given 

 that at high altitudes after acclimatization the lungs actively 

 secrete oxygen inwards even during rest, and that were it not so 

 the immunity from symptoms of mountain sickness among ac- 

 climatized persons would be totally unintelligible. It only remains 

 to discuss here some special points with regard to oxygen secre- 

 tion. 



The fact that some time is needed before oxygen secretion is 

 effectively established at a high altitude, accords exactly with the 

 fact that it takes a man some time to get his lungs and other parts 

 of his body into good physiological training for heavy muscular 

 exertion. As was p ointed out in Chapter IX there is now very 

 clear evidence that in persons who are in good training oxygen 

 secretion by the lungs plays a very important part, whereas in 

 persons not in training any secretion evoked by muscular work is 

 so feeble as to be quite ineffective. Both at high altitudes and in 

 training for muscular exertion the power of secretion develops 

 with use; and development occurs in exactly the same manner 

 with the exercise of all other physiological functions. At high 

 altitudes the stimulus to secretion originates in consequence of the 

 imperfectly saturated condition of the arterial blood; and al- 

 though after acclimatization is established the saturation of the 

 arterial blood with oxygen becomes less incomplete, yet part of 

 the incompleteness must remain; otherwise there would be no 

 stimulus to oxygen secretion. In this connection it should be noted 

 that the arterial oxygen pressure given by the carbon monoxide 

 method is the average oxygen pressure of the blood leaving the 

 alveoli, and not the oxygen pressure of the mixed arterial blood. 

 The latter value is undoubtedly a good deal lower for the reason 

 already explained. 



It h as for long been well known to mountaineers that persons 

 who^re in good physical training for hard work are far less 

 susceptible to mountain sickness and the other characteristic effects 

 of high altitudes than those who are not in training. This fact is 



