332 The Causes of Ahsorption of Oxygen hy the Lungs. 



with the same air outside the body, and vice versa. It is, of course, assumed 

 that carbon monoxide diffuses freely through the body, since, apart from its 

 property of combining with the hjemoglobin, it is, as was experimentally 

 shown by Haldane, a physiologically indifferent gas, like nitrogen or 

 hydrogen. 



Haldane and Lorrain Smith determined the constants required in their 

 calculations, not from experiments at body temperature on blood from the 

 animals experimented on, but on dilute blood solutions or undiluted human 

 blood. This omission, which in the then existing state of knowledge did not 

 seem important, has, we find, seriously affected their estimates of the oxygen 

 pressure in the arterial blood. The constant varies distinctly for the blood 

 of different animals, and even for different individuals of the same species. 

 We have, therefore, repeated the experiments, using mice, on which most of 

 Haldane and Lorrain Smith's experiments were made, and determining the 

 constant for the blood of each animal experimented on. We find that in 

 general their estimates of oxygen tension were about a third too high. 



We have also supplied an omission ;n their experiments by investigating 

 the arterial oxygen pressure in animals lireathing a very low percei>tage of 

 carbon monoxide (less than 0'02 per cent.), so that no physiological 

 disturbance is produced by the gas. 



Our results with mice are as follows : — 



1. When a very low percentage of carbon-monoxide is breathed, so that 

 no want of oxygen is produced in the body, tlie arterial oxygen pressure 

 is slightly helow the alveolar oxygen pressure. Apparently, therefore, the 

 absorption of oxygen is by difl'usion alone, as indicated by the experiments of 

 Fredericq and Krogh, and by most of Bohr's experiments. The results 

 agree closely with ]'>ohr's I'cceut calculations of tlie arterial oxygen pressure 

 which miglit be expected during rest if diffusion alone were in play. 



2. When a much higher percentage of CO is l:)reathed (0"2 per cent, or 

 more) the oxygon pressure in the arterial blood rises to nearly double that 

 of tlie alveolar air, and considerably above iJiat of the external air. With 

 intermediate percentages of CO there are inteniiediate riscis in the arterial 

 oxygen pressure. 



It is thus evident that, although under ndrnial resting conditions al)sorp- 

 tion of oxygen occurs only by dill'usion, want of oxygon in the tissues of the 

 body brings into ])Iay a sii])plementary secretory activity by which oxygen 

 is actively absorbed from the alveolar air into the blood. This i)rocess is 

 presumably analogous to tliat by which oxygen at a ])artial pressure of 

 sometimes as inucli as 100 atmospheres above that in tlic sea water is 

 secreted into the swim-Madder of deep-sea fishes. 



