THE PLACE OF BIOLOGY. 25 



air is diminished in proportion to the fall of atmo- 

 spheric pressure. Paul Bert's conclusions have again 

 and again been attacked or misunderstood by subsequent 

 writers, but as to their substantial correctness there is 

 not now a shadow of doubt. 



We selected Pike's Peak for the observations because 

 of the existence of a cog-wheel railway to the summit 

 at 14,100 feet, and a substantial building, in which we 

 were promised, and were given, excellent accommoda- 

 tion for ourselves and all our apparatus, and where 

 we had ample opportunities of observing the effects 

 of the air on the numerous people who came up. When 

 we first went up we were, like other newcomers, slightly 

 blue in the lips and face, and after a few hours began to 

 suffer from the very unpleasant symptoms of mountain 

 sickness. In the course of the next two or three days 

 these symptoms of oxygen- want passed off, and though 

 we were still unusually short of breath after muscular 

 exertion, we remained extremely well, and of a perfectly 

 normal colour, like the other persons living on the 

 summit. There was thus no doubt about the acclima- 

 tisation. Our measurements now showed that the 

 partial pressure of oxygen in the arterial blood was 

 considerably higher than in the air of the lung alveoli. 

 An active secretion of oxygen inwards into the blood 

 had thus, established itself, even during rest ; and on 

 this active secretion the main phenomena of acclimatisa- 

 tion depend, so far as we could judge. But for this 

 active secretion it would be hard to understand, for 

 instance, how the Due d'Abruzzi and his party could 

 have climbed in deep snow to a height of 24,600 feet 

 in the Himalayas. Even on Pike's Peak at only 14,000 



