Death in Closed Vessels 579 



What we say of carbonic acid is general for all poisonous gases 

 (CO, HS, etc.) ; only the numerical value of the lethal tension will 

 change. We shall return to this point when we speak of the 

 hygiene of workmen in compression tubes. 



C.— When the oxygen tension reaches about 300, whatever the 

 percentage and the pressure are (the latter evidently cannot be 

 lower than 3 atmospheres, with pure oxygen). 



D.— These kinds of death can be combined by twos, A with B 

 and B with C, according to the pressures and gaseous compositions 

 used. 



Death A is a real asphyxia for lack of oxygen; death B is a poi- 

 soning by carbonic acid; death C can be called, for convenience and 

 in spite of the strangeness of the expression, a poisoning by oxygen. 



We see— and this is the most general result reached— that in 

 all cases the barometric pressure in its variations is never directly, 

 of itself, the cause of the phenomena. It is only one of the condi- 

 tions which alter the tension of the gases, and the other factor, the 

 percentage, can completely offset its effects, if its progress is in 

 the other direction, just as it will increase them rapidly, if its 

 progress is in the same direction. 



If now we leave out the carbonic acid produced, to place our- 

 selves in conditions nearer those in which our present problem ap- 

 pears in nature or industry, setting aside certain phenomena which 

 are quite secondary and to which we shall return at the appropriate 

 time, we reach these conclusions: 



1. That three animals, the first of which exhausts by its respira- 

 tion a closed space full of air, the second of which is compelled to 

 breathe in a current of air of diminishing oxygen content, the third 

 of which is subjected to a gradual decrease of pressure, are all three, 

 by these different procedures, threatened by the same symptoms 

 and the same death, a death from lack of oxygen, a real asphyxia; 



2. That two animals, one of which breathes in a current of air 

 of increasing oxygen content while the other is subjected to a 

 barometric pressure increasing from 1 to 5 atmospheres, are in 

 identical conditions. That, besides, the animal which breathes pure 

 oxygen at 2, 3, 4 atmospheres, etc., is in the same conditions as the 

 one which breathes pure air at 10, 15, 20 atmospheres; both are, by 

 these different procedures, threatened by the same symptoms and 

 the same death, a death from excess of oxygen, a poisoning of a 

 sort hitherto unknown. 



All the influence which barometric modifications exercise on 



