56 THE ACTIVE FORCES OF LIVING ORGANISMS 

 The chief such meagre results ; nor is it intended here to do 



points. 



more than draw attention to some of its more salient 

 aspects. The degree of atmospheric pressure, the 

 amount of oxygen in the air and in the blood, the 

 proportion of carbonic acid in the blood, the effect of 

 electrical or ethereal conditions, and the mode of func- 

 tioning of the nervous centres in the race or in the 

 individual — these are points which appear to merit 

 consideration. 

 Theim- That animal life may exist in a state of normal 



portance _ '' 



of the health and activity at very great heights is clearly 

 factor. shown in the case of the condor, which, according to 

 Humboldt, flies as high as 21,834 feet ; whilst eagles 

 and vultures have even been observed by the Schlagin- 

 weits at a height of 23,000 feet above the sea.* These 

 facts considered in conjunction with the inability of 

 cats to withstand a height of only about 13,000 feet 

 point to the conclusion that the essential factor is 

 neither absolute atmospheric pressure nor the absolute 

 amount of oxygen in the air, but the readiness of the 

 nerve centres governing metabolism to adapt them- 

 selves to conditions more or less removed from those 

 to which the race or the individual has been habitually 

 subjected. In other words, a cat's blood exposed to 

 the air at a given level above the sea would probably 

 oxidize as fully and as rapidly as that of an eagle, 

 yet the transmission of oxygen from the blood to the 

 tissues and the formation of carbonic acid does not 

 take place in a regular manner in animals belonging 

 * Mosso, loc. cit., pp. 21, 22. 



