564 Experiments 



of 14 centimeters, noted in Experiment XLVIII. To reach the 

 average figure of 26, the percentage of carbonic acid in the lethal 



76 

 air must rise to 26 x — = 141, which is evidently impossible. In 

 14 



other words, before the bird can reach the lethal tension of carbonic 

 acid, it exhausts the oxygen of the surrounding medium, so that it 

 succumbs to the kind of death customary in diminished pressures, 

 when ordinary air is used. That is why we shifted to Sub-chapter 

 I the experiments made under these conditions. 



The analogy between these two kinds of experiments, apparently 

 so different, is seen again in a rather interesting experimental de- 

 tail, which, at first glance, seemed to me somewhat paradoxical. 

 When I supplied pure air to a bird which was beginning to suffer 

 from the effect of increased pressure, I did not relieve it at all; 

 on the contrary, an evident improvement appeared when I allowed 

 a part of its air to escape. This is easily explained; let us suppose 

 that the bird is under a pressure of 3 atmospheres and that it has 

 already formed 6 per cent of C0 2 ; the pressure of this gas, 6 x 3=18, 

 is enough to make the bird ill. If I admit 3 atmospheres of pure 

 air, the C0 2 tension becomes 3 x6=18, that is, it does not change 

 at all, since although the pressure increases one-half, the percentage 

 diminishes one-half; the bird is therefore not relieved. If, on the 

 contrary, I let out one-half of the air, the tension becomes 6 x 1.5 

 =9, so that an immediate betterment results. So this apparent 

 paradox confirms again, in an indirect way, what I have already 

 demonstrated. 



The same thing holds good for experiments at low pressures 

 with a superoxygenated atmosphere. Here, if the bird has been 

 made ill by the carbonic acid it has formed, it is not relieved if air 

 or oxygen is admitted; on the contrary, if the barometric pressure 

 is lowered, it is relieved. Let us take the case of a bird at 38 cm., 

 that is, at a half-atmosphere. Let us assume that it has already 

 formed 30 per cent of CCX; the CO, tension is 30 x ¥2 =15 and the 

 bird begins to suffer from it. Let us admit air until the pressure 

 is 57 cm., that is, three-quarters of an atmosphere. The percentage 

 will be only 30 x %=20, but the tension will be 20 x 3 / 4 = 15, and 

 the bird will be in the same state as before. If, on the contrary, 

 we remove air and drop the pressure, for example, to 19, V\ of an 

 atmosphere, the percentage of carbonic acid will not have changed, 

 and its tension will be only 30 x 1 /4=7.5, a tension almost harmless 

 to the bird, which will be relieved immediately. 



