1150 



PHYSIOLOGY 



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. 519, 

 p. 1132). 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 diminution 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. 



As a result of the oxygen starvation there is inadequate supply of this 

 gas 10 the heart, so that the circulation tends to fail, especially on making 

 the slightest muscular movements. At the same time the oxygen starva- 

 tion of the brain produces failure of judgment and inability to carry out or to 

 co-ordinntt' muscular movements properly. The symptoms as a rule do not 

 increase until death results, so that, although there is an oxygen starvation 

 of the body, there must be some means by which the respiration is modified 

 so as to obtain a sufficiency of this gas for the lowered requirements of the 

 body. That the adaptation is effective is shown by the fact that most 



