Action of Carbonic Acid 921 



and the tracing in Figure 78 which was made by the pneumograph 

 (Exp. DCXV), shows that the cessation of the respiratory move- 

 ments took place without a last sigh: this in itself as I proved 

 elsewhere', indicates that carbonic acid is not a heart poison. 



During the whole duration of this progressive poisoning, the 

 animals remain perfectly calm. At the beginning, only a few 

 struggles, which soon are quieted. If the animal is unfastened 

 when the arterial blood contains 60 or 70 volumes of CO., it makes 

 no attempt to escape. Later, it becomes insensible to stimuli, to 

 pinching, even to electrical stimulation of the sensory nerves: 

 finally the eye itself becomes insensible. 



This curious anesthesia deserves our attention for a few 

 minutes. 



Let us say first that insensibility to pinching occurs long before 

 the animal is threatened by death. In Experiment DCVI, the eye 

 was insensible two hours before death, when there were still 10 

 respirations, and 64 heart beats, the temperature having fallen to 

 30 degrees; in Experiment DCXIV, the paws became insensible 

 more than four hours before death, and the eye two hours (respira- 

 tions 20; pulse 43; temperature 27°); finally in Experiment DCXV, 

 absolute insensibility of the paws was observed more than three 

 hours before death, and the eye became insensible two hours before 

 (respirations 20; pulse 48; temperature 29.5°). 



This insensibility is very complete; stimulation of the sciatic 

 nerve by pinching or electric currents causes no general movement, 

 no change in the respiratory rhythm (Exp. DCXV) , in the arterial 

 pressure or the state of the pupils (Exp. DCXVI) , even when they 

 still contract under the direct influence of light. The eye, as I have 

 just said, keeps its sensitivity for a long time yet, and this sensi- 

 tivity disappears last in the conjunctiva (Exp. DCXIII). 



Now when the eye has become absolutely insensible, the animal 

 is by no means in danger. If it is taken from the altered medium 

 and brought into the air, it always recovers (Exp. DCXII, DCXIII, 

 DCXVI, DCXVII, DCXVIII, DCXIX), generally after displaying 

 strange symptoms, to which I shall call attention presently. 



If we investigate the proportion of carbonic acid in the air and 

 the arterial blood at which insensibility of the feet or of the eye 

 occurred, this is the average we obtain: insensibility of the feet 

 appeared when the air contained about 28% of carbonic acid, 

 and insensibility of the eye when the proportion rose to 35%; for 

 the blood, the extremes are much wider, since they vary from 72.3 

 (Exp. DCXII) to 95.4 (Exp. DCXV) . 



