EFFECTS OF CHANGES IN AIR BREATHED 



1227 



MOUNTAIN SICKNESS. The phenomena just described as en- 

 suing on exposure of an animal to low oxygen tensions in a respiratory 

 chamber for some length of time are exactly similar to those which 

 are regarded as characteristic of mountain sickness. The following 

 table shows the diminution in the atmospheric pressure at varying 

 heights above the level of the sea : 



At a height of 5000 metres the pressure of the air is reduced to 

 little over half an atmosphere and the oxygen tension is therefore only 

 about 11 per cent, of an atmosphere. It must be remembered that in 

 most cases of mountain sickness, in addition to this absolute oxygen 

 lack, there is increased consumption of oxygen, owing to the muscular 

 exercise involved in climbing. Moreover a greater volume of the alveolar 

 air must consist of carbon dioxide if the tension of this gas is to be 

 kept constant (cp. Fig. 504, p. 1207). Since diminished oxygen tension, 

 within fairly wide limits, does not excite any corresponding increase 

 in the respiratory movements, there must, at these heights, be an 

 actual diminution in the oxygen tension in the alveoli. This diminu- 

 tion in tension is shown by a series of observations carried out by 

 Zuntz on himself and fellow workers at different localities. It may be 

 noted that on Monte Rosa, where the oxygen tension in the alveoli was 

 reduced to between 37 and 57 mm. Hg, as against the normal 101 

 to 105 mm. Hg, all the members of the party were suffering from 

 mountain sickness. 



