80 THE LAW OF BIRTHS AND DEATHS 



surprised that they are rather more fertile when brought 

 down to the relaxing air of the lowland pastures. 



In this connection some facts mentioned by Ellsworth 

 Huntingdon are worth noting. "It is well known/' he 

 says, " that at high altitudes the number of red corpuscles 

 in the blood increases enormously, and the capacity to 

 absorb oxygen and give out carbon dioxide is correspond- 

 ingly modified." 1 He quotes the experiments of Lehman 

 and Pederson in Denmark and Norway, who found that 

 a change of atmospheric pressure due to an ascent of 

 two or three thousand feet made no appreciable difference 

 to the strength of individuals as measured by the dynamo- 

 meter, but that a similar descent is accompanied by a 

 marked increase in strength which, however, disappears 

 in about four days. It was suggested to him by Prof. 

 H. E. Gregory that this may account for the fact that 

 in the horse-races of the pioneer days of the south-western 

 United States " the poor, scrawny animals brought down 

 from the mountains by the Indians usually belied their 

 appearance and outran the better-looking horses of the 

 white man. They may have had an excess of red cor- 

 puscles." As the increased energy displayed lasts only 

 four days, there is nothing in these facts inconsistent 

 with the fact that mountain sheep become more fertile 

 in the lowland pastures. But it becomes a question 

 whether the increase of red corpuscles in the blood at 

 high altitudes may not account, in some measure, for 

 the greater activity of mountain sheep, and also for their 

 relative infertility. It is true that the experiments 

 showed no increase of strength during the ascent, but 

 time may be needed for that. It is a remarkable fact 

 that all mountain species seem to display this abnormal 

 activity. 



1 Civilisation and Climate, p. 60. 



