Action of Carbonic Acid 897 



And so, the higher the pressure, the lower may be the per- 

 centage necessary to cause death, and vice versa. Likewise, at 

 normal pressure and pressures below normal, to produce death, the 

 animals must have been confined in superoxygenated air, for ordi- 

 nary air could not furnish the 24 to 28 per cent lethal at one at- 

 mosphere, the 48 to 56 per cent lethal at a half-atmosphere, etc. 

 This is, in fact, what the numerous experiments listed in Chapter 

 I showed us. 



1 have made a good many experiments upon animals of different 

 species, from which it appears that the value of the lethal tension 

 of carbonic acid varies according to the species. 



Here, for example, are two experiments on rats: 



Experiment DXCVI. August 5. 



Rat placed at 3 o'clock in the small Seltzer water receiver, at 7 

 atmospheres. 



Found dead at 6 o'clock; the muscles still contract. 



Lungs inflated to the maximum, not retracting when the chest 

 was opened; gases expanded in the stomach. 



Gas in the blood of the right heart, but not in the left heart. 



Lethal air, CO, 4.4; O, 14.8. 



CO, tension = 30.8. 



Experiment DXCVII. August 19. 



Rat weighing 180 gm., placed at 11:45 at 7 J/ 2 atmospheres. 



Same apparatus; dies at 2 o'clock. 



Enormous expansion of the gases of the stomach. 



No gas, even in the right heart. 



Lethal air, C0 2 4; O, 14.3. 



CO, tension = 30.0. 



We see here that the lethal tension of carbonic acid is, for rats, 

 a little higher than for birds. 



That is, furthermore, a general fact in mammals, as will be 

 proved presently by the experiments made on dogs, which experi- 

 ments will give in addition the explanation of the apparent irregu- 

 larities in the value of the lethal tension. I did not think I should 

 dwell on these differences from species to species; only one, which 

 I mentioned before, 1 deserves to be recalled here, as I shall recall 

 elsewhere the general conclusion. This difference is that batra- 

 chians and reptiles find carbonic acid much more dangerous than 

 do warm-blooded animals. Here are some experiments to support 

 this important proposition. Some were made by using superoxy- 

 genated air at normal pressure: 



