922 Experiments 



This complete anesthesia of the limbs, when the eye is still 

 sensitive, when the heart still beats frequently and strongly, and 

 when the animal is still so far from serious danger, naturally in- 

 spired the idea of a possible surgical application. 



But an important difficulty appeared. In the experiments which 

 I have just reported, the animal itself forms the carbonic acid 

 which it stores up in its blood and tissues; that requires a very long 

 time. In Experiment DCXIII, insensibility of the paws was ob- 

 served only after two hours; it took more than three hours in Ex- 

 periments DCXIV and DCXV. Nothing would be less practical 

 than this long preparation, which would be a long torture. On the 

 other hand, and this is still more important from another point of 

 view, in these long experiments the temperature had dropped sev- 

 eral degrees at the time when insensibility of the paws appeared, 

 and that might have serious consequences for the patients. 



I then asked myself whether I could obtain results similar to the 

 preceding ones by making the animals breathe a more or less rich 

 mixture of carbonic acid and oxygen early in the experiment. I 

 did this in Experiments DCXVI, DCXVII, DCXVIII, and DCXIX. 



When the mixture to be breathed contained 207c of carbonic 

 acid (Exp. DCXVII), insensibility appeared only after IV2 hours, 

 at which time the temperature had dropped 4°, the respirations 

 numbered 36, and the pulse rate was 100; the arterial blood then 

 contained 77 volumes of CCX. But with 40% of C0 2 (Exp. DCXVI, 

 DCXIX) insensibility occurred after 3 or 5 minutes, of course 

 without a change in the temperature, the heart having singular 

 strength, (19 to 23 cm., Exp. DCXVI; 18 to 20 cm., Exp. DCXIX) 

 greater than in the normal state: the arterial blood contained 78.6 

 volumes (Exp. DCXIX) or 81.2 volumes (Exp. DCXVI) of carbonic 

 acid. 



Finally, with a mixture containing 52.8% of C0 2 , insensibility 

 was almost instantaneous, and the arterial blood was laden with 98.4 

 volumes of CO, (Exp. DCXVIII) . 



These last results show that the surgical use of carbonic acid, 

 in a proportion of about 40%, the rest of the gas being nearly pure 

 oxygen, might give good results, and would not at all affect arterial 

 pressure, as do the compounds of carbon and hydrogen and the 

 chloro-carbon compounds of hydrogen. 



But this proportion of carbonic acid in the respirable medium 

 must not be much exceeded. I showed in 1864 4 that if two new- 

 born rats were placed, one in carbonic acid, the other in nitrogen, 

 the heart of the latter continues to beat more than a quarter of an 



