Decreased Pressure 1001 



But after all, acclimatization, at least apparent, not only of na- 

 tives but also of temporary residents, is a certainty, when the 

 elevation does not exceed certain limits. How does it happen? To 

 say that they have become accustomed to these new conditions 

 explains nothing, although ordinarily we are compelled to use this 

 vague expression to designate everyday observations. How does it 

 happen that a certain day of average temperature seems to us warm 

 in winter, chilly in summer? That a certain room with closed 

 shutters is dark at first, whereas its slightest details are lighted 

 up after a few minutes? In the particular case we are discussing, 

 we understand very well that, on the one hand, organs accustomed 

 to being irrigated by an arterial blood with 20% of oxygen, accus- 

 tomed to live by borrowing from this blood 8 volumes of oxygen 

 easy to dissociate, complain and revolt when the arterial blood 

 brings them only 16 volumes, from which it becomes harder to 

 extract the 8 volumes necessary for inner consumption, and that, 

 on the other hand, at the end of a few days or weeks of more or 

 less painful transition, they progressively alter their first impres- 

 sion, exert themselves, and are more able to manage the somewhat 

 more difficult dissociation to which they are forced. But all this, 

 to tell the truth, is only a paraphrase of the expression "habit," and 

 explains little; we need to know what this inner modification of 

 the tissues consists of, and today we are unable to get the least 

 idea of it. 



What is really certain is that this traveller, now a dweller in 

 lofty altitudes, does not even try to struggle against the decrease 

 of oxygen in his arterial blood by speeding up his respirations ex- 

 cessively, as was at first supposed. The observations of Dr. Jour- 

 danet are conclusive (p. 265). And that is easily understood. First 

 the gymnastics which one must perform to ventilate his lungs with 

 the same weight of air at 48 cm. as at 76 cm. evidently cannot be 

 kept up, even for a few minutes. In the second place, they would 

 hardly be effective, since our experiments have shown (See Figure 

 43, graphs B and C) that at this pressure saturation of the blood 

 by perfect agitation cannot add more than a volume and a half of 

 oxygen, and besides, at normal pressure, there is usually the same 

 average difference between the oxygen content of the arterial 

 blood and its maximum capacity. However a slight increase of 

 this sort would not be useless, and it could be produced either by an 

 acceleration or by a greater amplitude of the respiratory move- 

 ments. The first phenomenon does not take place, according to 

 M. Jourdanet; the study of the second would present great difficul- 



