ABSORPTION OF OXYGEN IN THE LUNGS. 



261 



v. 



0-Tension in the air of the alveoli of the 

 catheterised lung = 27 '44 mm. Hg. 

 (corresponding to 3 '6 vol. per cent.) 



VI. 



CO 2 -Tension in the air of the alveoli of 

 the catheterised lung = 27 mm. Hg. 

 (corresponding to 3 '56 vol. per cent.) 



VII. 



0-Tension in the atmosphere = 158 mm. 

 Hg. (corresponding to 20 '8 vol. per 

 cent.) 



VIII. 



COg-Tension in the atmosphere = 0'3S 

 mm. Hg. (corresponding to '03-0 '05 

 vol. per cent.) 



When we compare the tension of the in the air (VII. = 158 mm. 

 Hg.) with the tension of the in venous blood (III. = 22 mm. Hg., or 

 V. 27*44 mm. Hg.), we might be inclined to assume that the passage 

 of the from the air of the air-vesicles into the blood was due solely 

 to diffusion of the gases; and similarly, we might assume that the 

 C0 2 of the venous blood (IV. or VI.) diffused into the air-vesicles, 

 because the tension of the C0 2 in the air is much less (VIII.) There 

 are a number of facts, however, which prove that the exchange of the 

 gases in the lungs is chiefly due to chemical forces. 



Absorption of 0. With regard to the absorption of from the air 

 in the alveoli into the venous blood of the lung capillaries, whereby 

 the blood is arterialised, it is proved that this is a chemical process. The 

 gas-free (reduced) haemoglobin takes up to form oxyhsemoglobin ( 15, 

 1 ). That this absorption has nothing to do directly with the diffusion 

 of gases, but is due to a chemical combination of the atomic compounds, 

 is shown by the fact, that, when pure is respired, the blood does not 

 take up more than when atmospheric air is respired ; further, that 

 animals made to breathe in a limited closed space can absorb almost all 

 the even to traces into their blood before suffocation occurs. Of 

 course if the absorption of were due to diffusion, in the former case 

 more O would be absorbed, while in the latter case the absorption of 

 could not possibly occur to such an extent as it does. 



The law of diffusion comes into play in connection with the absorp- 

 tion of to this extent, viz., that the diffuses from the air-cells of 

 the lung into the blood-plasma, where it reaches the blood-corpuscles 

 suspended in the plasma. The haemoglobin of the blood-corpuscles 

 forms at once a chemical compound (oxyhsemoglobin) with the 0. 



Even in very rarifted air, such as is met with in the upper regions of the 

 atmosphere during a balloon ascent, the absorption of still remains independent 

 of the partial pressure (Loth. Mayer, Fernet). But a much longer time is required 

 for this process at the ordinary temperature of the body, so that in rarified air, the 

 absorption of is greatly delayed, but it is not diminished. This is the cause of 

 death in aeronauts who have ascended so high that the atmospheric pressure is 

 diminished to one-third (Setschenow). 



Excretion of C0 2 . With regard to the excretion of C0 2 from the 

 blood, we must remember that the C0 3 in the blood exists in two con- 



