418 THE RESPIRATION 



mia itself or the slight degree of alkalosis induced by the lowered C0 2 - 

 tension that is the cause for these symptoms cannot at present be said. 



The susceptibility of different individuals also varies according to the 

 amount of previous experience in mountaineering and the type of breath- 

 ing. Much of the value of previous experience and training depends on 

 the ability to perform muscular effort economically; to adjust the effort 

 to the available oxygen supply without causing aggravation of the symp- 

 toms of anoxemia. It often happens that no symptoms appear so long as 

 the person is at rest, but immediately do so whenever any muscular 

 effort is attempted. 



The type of breathing that best withstands the rarefied air is slow and 

 deep, rather than rapid and shallow. The reason for this is of course 

 that much more of the outside oxygen gets into the alveoli in the former 

 case than in the latter, the dead space being practically constant. The 

 following figures taken from observations on three different individuals 

 will illustrate the importance of this factor. 



(From Halliburton.) 



After living for some time in the rarefied air and quite independently 

 of training in the efficient performance of muscular work, adaptation 

 occurs, so that the symptoms pass off. The essential feature of this adap- 

 tation is increased absorption of 2 into the blood. Three mechanisms 

 have been described as responsible for this effect: (1) increase in the ten- 

 sion of 2 in the alveolar air; (2) assumption by the pulmonary epithelium 

 of the power of secreting 2 into the blood; (3) increase in the erythrocytes 

 and hemoglobin of the blood. The increased alveolar 2 tension is a result 

 of the increase in pulmonary ventilation. If no adaptation occurred, the 

 2 tension at 10,000 feet would be 59 mm. and at 15,000 feet, 33.8 mm. 

 Actual observations on men, however, gave at 10,000 feet a tension of 65 

 mm. and at 15,000 feet, 52 mm. 



The evidence for an increased secretory activity of the pulmonary 

 epithelium depends on observations made by Haldane and his cowork- 

 ers, 33 who found that blood collected from the finger of a man living on 

 a high mountain is brightly arterial, whereas if this same blood is 

 shaken in a flask with alveolar air from the man from whom it was 

 taken, it will become darkly venous. To account for this difference it is 



