1152 



PHYSIOLOGY 



oxygen tension, any diminution in oxygen tension must cause a corresponding 

 diminution in the degree of saturation of the haemoglobin of the blood. This 

 change in oxygen saturation is at once felt by the blood-forming organs. 

 As an immediate effect of change to a region of low atmospheric pressure, 

 there is a relative increase in the blood corpuscles due to a concentration 

 of the blood and a diminution of its plasma. Simultaneously however 

 the blood-forming organs enter into a condition of increased activity, so 

 that after a stay of four or five weeks' duration at a height, both corpuscles 

 and haemoglobin are considerably increased in total amount. The following 

 Table shows the average number of red corpuscles contained in one cubic 

 millimetre of blood from the inhabitants of regions at varying altitudes : 



There is of course a limit to the power of adaptation, a limit which varies 

 in different individuals. Thus for some men it is impossible to stay any 

 length of time in the high settlements in the Andes, while others, after two 

 or three weeks' discomfort, become perfectly inured to their new conditions. 

 It seems doubtful however whether any of the present race of men could 

 become adapted to permanent residence at a height over 5000 metres, and 

 though for a certain length of time by bringing into play the reserve 

 mechanisms already described, they may raise themselves to a height 

 considerably above 5000 metres, it seems questionable whether without 

 artificial means, such as the inhalation of oxygen, it will be possible for 

 any man to attain the highest points on the earth's surface, or at any rate 

 to arrive there by his own unaided efforts. The highest summits in the 

 Himalayas have a height approaching that attained by Tissandier with his 

 two companions in his famous Jmlloon ascent, namely, 8600 metres. In this 

 ascent, although oxygen inhalation was used (somewhat ineffectively), two 

 of the party succumbed. 



The stimulating effect of oxygen lack on the blood-forming organs 

 extends also to the muscular 'system, so that one of the effects of a residence 

 in high altitudes is increased assimilation of nitrogen. For a time the 

 nitrogen output is less than the nitrogen intake, and there is an actual 

 building up of new tissue. The condition of the individual is similar to that 

 of a growing animal, a fact which may explain the admirable results of a 

 mountain holiday. We can hardly imagine that the power of the organism 

 to react in this way was evolved through generations of mountain climbing. 

 We are probably here making use of an adaptation which has been evolved 

 for the purpose of retrieving loss of blood by haemorrhage, such as must have 



