542 Experiments 



These last barometric pressures are very low, and quite evidently 

 the transitions had not been careful enough. 



Experiment LVI. August 3, hawk (Falco tinnunculus, Lin.). Pres- 

 sure 75.5 cm. Bell-jar of 13.5 liters. 



Began at 3:25; current of air. The decompression at 3:30 is 8 

 cm.; at 3:35, 16 cm.; at 3:45, 30 cm.; at 3:50, 40 cm.; at 3:53, 50 cm.; 

 that is, actual pressure about 25.5 cm. Bird vomits and falls; pressure 

 raised to 31.5 cm., then slowly lowered to 25.5 cm.; the bird, which 

 had recovered a little, falls again, seems about to die, and the pres- 

 sure has to be raised to 27.5 cm. 



At 4:05, pressure is 25 cm.; at 4:10, 24.5 cm.; at 4:15, 21.5 cm.; 

 the bird vomits, staggers, and reels, but seems to recover a little, while 

 remaining weak. At 4: 17, the pressure is only 20 cm.; at 4:20, 19.5 cm. 

 Cocks are closed, and the bird dies at 4:32. Lived about 40 minutes 

 with respiratory embarrassment. Eight minutes after death, rectal 

 temperature was 37.4°. 



The air, as one might expect, is hardly altered; C^ 20.0; CO 0.8. 



Oxygen tension = 5.1. 



The interesting point of this last experiment is that a bird of 

 prey, zoological neighbor of the vultures and the condors which 

 mount to prodigious heights, was at least as sensitive to the lower- 

 ing of pressure as a simple sparrow. 



B. Experiments on Mammals. 



These have been rather few, since the principal point of the 

 question had been settled by the experiments on sparrows. They 

 have shown me, as a general fact, that mammals can be brought 

 to pressures considerably lower than birds. One might have con- 

 jectured as much anyway, since mammals deplete the oxygen of 

 the confined air more than birds do. (See my Lessons on the 

 Physiology of Respiration, page 510.) 



They are, besides, more pliable, so to speak, that is, easier to 

 reduce to the state of cold-blooded animals, enduring then as the 

 latter do, extremely low pressures (See later) ; this is especially 

 true of rodents. A remarkable example of this fact (Exp. LVII) 

 was shown by a guinea pig, which, having been placed for four 

 hours in a current of air (temperature 15°) , continued to live under 

 a pressure constantly lower than 20 cm., which was repeatedly 

 lowered to 11 cm. for four or five minutes. It is true that after this 

 time the unfortunate animal remained motionless, almost uncon- 

 scious, with a rectal temperature of 20°, and that it died several 

 hours after the experiment. 



In another case (Exp. LVIII) , a guinea pig was brought to and 

 maintained at a pressure of 12 cm. for about a quarter of an hour, 



