558 Experiments 



In the present experiments, Column 9 furnishes us analogous fig- 

 ures only for the pressures between 1 and 2 atmospheres. And 

 even here there appear already the numbers 8 and 10, which soon 

 become 20 and 40, and finally 113 and 153 at the pressures of 7 and 

 8.8 atmospheres. 



So then, above 2 atmospheres, death in confined air cannot be 

 attributed to lack of oxygen; we must seek some other cause. 



My first thought naturally turned to carbonic acid. 



Now considering Column 8, in which are listed numbers ob- 

 tained by multiplying the percentage of carbonic acid by the num- 

 ber of atmospheres, and which consequently represent the car- 

 bonic acid tension in the lethal air, we see that, from 2 atmospheres 

 on, these numbers oscillate between 25 and 30. 



If now we refer to what M. Claude Bernard" said formerly about 

 the conditions of death of birds confined at normal pressure in 

 superoxygenated air, we see that they die when they have formed 

 a proportion of carbonic acid which corresponds precisely to that 

 which we have just indicated. The numerous experiments which 

 I myself 4 have carried on in this field have led me to similar results, 

 and I have confirmed the accuracy of the explanation given by 

 CI. Bernard of this strange asphyxia in a medium much richer in 

 oxygen than ordinary air. It is a real poisoning due to the carbonic 

 acid of the blood, which cannot be eliminated because of the 

 pressure exerted upon it by the carbonic acid contained in the 

 ambient atmosphere. 



The cause of death, then, is the pressure exerted by this carbonic 

 acid, a pressure measured exactly at one atmosphere by the per- 

 centage of carbonic acid present. At pressures above one atmos- 

 phere, the real pressure, the tension of the carbonic acid, is 

 obtained by multiplying the percentage by the number of atmos- 

 pheres, and in this way we obtained the figures in Column 8. 



We can now give, for death in closed vessels, at pressures greater 

 than one atmosphere, a formula quite analogous to the one wa 

 gave earlier (see page 552) for pressures lower than one atmos- 

 phere, and say: The death of sparrows occurs when the tension 

 of the carbonic acid, measured as I have just specified, is repre- 

 sented by a figure which oscillates between approximately 24 and 

 30; hereafter we shall take 26 as an average number. 



The result of this fact is that, if we represent our results by a 

 curve resembling that of Figure 17, in which the abscissae would 

 represent the pressures, and the ordinates the proportions of car- 

 bonic acid, this curve would correspond to the formula xy = 25 to 



