Decreased Pressure 977 



and also by the immediate exposure of a pulmonary parenchyma 

 retractile at a considerably weakened outer atmospheric pressure, and 

 by the annulment of the compensating function of the glottis. (P. 341.) 



First, according to M. Campana, the movements of the wings 

 would put in play part of the aerial sacs (brachial prolongations 

 of the anterior-superior receptacle) situated between the motor 

 muscles of the wing sacs which remain motionless except in flight; 

 they would dilate at the elevation of the wing (that is, according to 

 the observations of M. Marey, at the moment of the tracheal in- 

 spiration), and would empty themselves of air at its lowering. 

 The result would be a considerably more rapid circulation of air 

 through the lungs, a more perfect ventilation, which would have 

 as a consequence that: 



In the same conditions where mountain sickness appears in mam- 

 mals, birds in flight escape the two causes of anoxyhemia which at- 

 tack mammals, if not absolutely and indefinitely, at least to a much 

 greater degree. (P. 341.) 



I consider the observations of M. Campana about the develop- 

 ment of air cells in the wings during the act of flight as perfectly 

 correct. But I think he has greatly exaggerated the importance 

 of this observation; first, the increase in volume acquired in this 

 way is not very great, considering that of the other gaseous reser- 

 voirs which act at the same time, that is, the extra-thoracic sacs. 

 In the second place, if I saw these aids of the respiratory act de- 

 veloping only during flight at great heights, I should admit that 

 they might then offer a certain utility: but they act equally at all 

 heights, provided that the bird is flying; and even if I believe that 

 they help thus to produce the increase of strength necessary for 

 work in the air and to establish the equilibrium of the organism 

 in a dynamic state, I do not understand how they can add, when 

 the low pressure becomes dangerous, a supplement of ventilation 

 and consequently of oxygenation which had not been already fur- 

 nished in the lower levels. Finally, even admitting that ventila- 

 tion is made perfect, we have seen that that is of little importance, 

 because it is the capacity of the blood for oxygen which constitutes 

 the real danger, since it has diminished with the height. The per- 

 fection of the ventilation can play only a very small role, since 

 it can only raise the quantity of oxygen contained in the arterial 

 blood in circulation to the amount which this blood would be 

 capable of absorbing if it was suitably saturated. This increase 

 is not to be scorned in mammals, and we shall dwell upon this 

 point in the following subchapter. But we ought hardly speak 



