978 Summary and Conclusions 



of it in birds, because, according to the recent research of M. 

 Jolyet, 21 their arterial blood is always nearly saturated with oxy- 

 gen; that, let us say in passing, is a fact of the greatest interest, 

 since it shows that in birds, contrary to the situation in mammals, 

 the conditions for the mixture of blood and air are perfect in the 

 respiratory apparatus. 



The second reason indicated by M. Campana to explain the 

 resistance of birds of lofty flight is: 



That they possess the means of removing the pulmonary paren- 

 chyma and up to a certain point the middle receptacles themselves 

 from the absolute dependence upon the barometric pressure which 

 the lungs of mammals endure necessarily during the inspiration. 

 (P. 342.) 



In other words, during the inspiration as during the expiration, 

 the lungs, in consequence of the energetic injection carried on 

 alternately by the extra- and intra-thoracic receptacles, "are 

 crammed with air under a pressure greater than that of the outer 

 air." (P. 343.) 



And so, the respiratory apparatus is removed up to a certain point 

 from the barometric pressure, which makes possible the ascent into 

 the higher levels of the atmosphere, and a fortiori the soaring flight 

 in the bosom of an icy and asphyxiating air. 



I do not wish to report or discuss the details of the very com- 

 plicated mechanism by which M. Campana explains this com- 

 pression of the air in the interior of the lungs; in short, it amounts 

 to an injection of air too great for the section of the delivery open- 

 ings in the meshes of the pulmonary parenchyma. But I cannot 

 admit that such great importance should be attributed to this 

 slight excess of pressure, or that we should consider it as offsetting 

 the enormous decompression to which the bird will be exposed; 

 these intra-pulmonary modifications can be reckoned in millimeters 

 of mercury, whereas the outer decompression is measured by tens 

 of centimeters. 



To my notion the question rests, and the immunity of condors 

 and vultures remains unexplained to me. Even if a study of the 

 effect of decompression in closed vessels should show us one of 

 these birds resisting much more than did our hawk, we should 

 be embarrassed by a sort of contradiction, but we should still have 

 no explanation. I shall return to these data in the next sub- 

 chapter when I speak of dwellers in high places, who seem to pre- 

 sent a similar immunity, like the yaks of the Himalaya and the 

 llamas of the Andes. 



