350 DR. STEVENS ON THE THEORY OF RESPIRATION. 



quantity of the carbonic acid ; but no oxygen appeared to have passed out of the 

 tumbler. 



11. A piece of moist bladder was tied over the mouth of a tumbler containing car- 

 bonic acid ; this was introduced into a bell glass filled with pure oxygen. In a short 

 period the membrane became concave, and the oxygen in the larger vessel was found 

 to be mixed with carbonic acid. 



These two experiments prove that oxygen possesses the power of attracting carbo- 

 nic acid, even through the medium of a membrane which is much denser than that 

 interposed in the lungs betwixt the air and the blood ; consequently, the extreme de- 

 licacy of the pulmonary membrane can be little impediment to the transmission of 

 carbonic acid in the process of respiration. 



I have ascertained that such transmission, or, in other words, the peculiar power by 

 which oxygen abstracts carbonic acid from the blood, is more energetic in a high 

 than in a low temperature. Hence venous blood drawn in a warm room changes 

 colour more rapidly than blood drawn in a cold atmosphere. 



12. A few ounces of venous blood were drawn into the double-necked bottle which 

 had been previously filled with pure oxygen ; the valves were closed, the blood was 

 well agitated with the gas, and the colour immediately changed from venous to arte- 

 rial. The bottle was allowed to stand about half an hour, and was then placed under 

 the receiver of an air-pump. When the pump was used the oxygen was found to be 

 strongly impregnated with carbonic acid ; in fact, the first bubbles of air which passed 

 through the barytic water rendered it milky. 



From the rapidity of the change of colour from venous to arterial, or from dark to 

 florid, in this experiment, it seems very improbable that any carbonic acid shoidd 

 have been ybrmec? in the blood, but that, on the contrary, it had previously existed in 

 the blood, and that the whole of this blackening gas had been instantly removed by 

 the oxygen. 



13. A piece of the intestine of a rabbit that had been recently killed was filled 

 \dth carbonic acid, and suspended in a bell glass containing owygen. In a short pe- 

 riod the acid escaped, and the intestine became quite flaccid. 



14. A piece of intestine, similar to that used in the last experiment, was filled with 

 oxygen, and suspended in a bell glass of carbonic acid ; the intestine began to swell 

 almost immediately, and in three minutes it burst. 



15. The lung of a rabbit was filled with oxygen, and suspended in a bell glass of 

 carbonic acid ; it began to swell almost instantly, and in one minute it burst. 



16. The lung of a rabbit was carefully inflated with carbonic acid, and was then 

 suspended in a bell glass of oxygen. In a very short period it became flaccid, and the 

 external oxygen was impregnated with carbonic acid. 



These experiments show how admirably the structure of the lungs is adapted for 

 the action of oxygen on carbonic acid. Vitality may have some share in accelerating 

 this process in the pulmonary organs, but we know that by the agency of oxygen 



