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. For many years it 

 has been claimed that this adaptation was due chiefly to the development 

 of a secretory activity by the pulmonary epithelium. Oxygen was 

 thought to be forced into the blood in quantities much greater than would 

 be the case if the pulmonary epithelium acted as a passive membrane 

 across which oxygen moved by a simple process of diffusion. As a result 

 of the recent development of the method of arterial puncture, it has been 

 shown that the blood of men thoroughly acclimated to life at an altitude 

 of 14,000 feet in the Andes, when drawn directly from the radial artery 

 without exposure to air, is darkly venous in color. Analysis shows that the 

 tension of oxygen in it is no greater than that existing in the alveolar air, 

 nor is the quantity of oxygen greater than would be taken up by the 

 blood when exposed to air of composition similar to that found in the 

 alveoli of the lungs. In view of these facts it is apparent that it is 

 unnecessary to assume any secretory function on the part of the pul- 



