EFFECTS OF CHANGES IN AIR BREATHED 



1229 



This quickening of the pulse is to be observed also in the trained 

 mountain soldier, in individuals in whom there is no lowering of the 

 alveolar carbon dioxide tension, so that apparently in such cases 

 the whole adaptation to altered conditions is by means of the circula- 

 tion. In cases where adaptation fails it is in the circulation that 

 the failure is most marked, so that the symptoms of severe mountain 

 sickness resemble closely those produced by rapid heart -failure. 

 Dilated heart, cyanosis, muscular weakness, vomiting, mental torpor, 

 inco-ordination, delirium, may all be observed in both cases. The 

 disturbance of the central nervous system is shown by the almost 

 invariable occurrence at great heights of Cheyne-Stokes breathing. 



If the animal is able to withstand the immediate effects of 

 exposure to a rarefied atmosphere, a process of adaptation comes into 

 play which finally fits him for discharging his functions normally even 

 at the high altitude. From the lack of sensibility of the respiratory 

 centre to small changes in oxygen tension, any diminution in oxygen 

 tension must cause a corresponding diminution in the degree of satura- 

 tion of the haemoglobin of the blood. This change in oxygen satura- 

 tion 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 



