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The Causes of Ah sorption of Oxygen by the Lungs 

 [Preliminary Communication). 



By C. Gordon- Douglas, B.M., Fellow of St. .lohu's College, and 

 J. S. Haldaxe. M.D., F.R.S., Fellow of New College, Oxford. 



(Received February 22,— Read March 10, 1910.) 



It has for long been a subject of controversy among physiologists whether 

 the absorption of oxygen through the walls of the lung alveoli into the blood 

 occurs simply l)y diffusion or by an active physiological process analogous to 

 glandular secretion.* Pfliiger, Fredericq, and, quite recently, Krogh,f have 

 brought forward experimental evidence in favour of the diffusion theory, while 

 Bohr, and Haldane and Lorrain Smith have supported the secretory theory, 

 which was originally suggested by Ludwig. 



If the partial pressure of oxygen is ever greater in the arterial blood 

 leaving the lungs than in the air of the lung alveoli, it is clear that the 

 simple diffusion theory must fall to the ground ; and the experiments hitherto 

 made have been designed to ascertain whether or not the oxygen pressure 

 in the arterial 1 )lood is ever greater than in the alveolar air. Bohr, Fredericq, 

 and Krogh have with this object employed improved forms of Ptluger's well- 

 known " aerotonometer," the instrument finally devised by Krogh being very 

 perfect of its kind. Haldane and Lorrain Smith's method depends upon the 

 following facts : — When blood is brought into prolonged and intimate contact 

 with a mixture of carl)on monoxide and air the haemoglobin of the blood- 

 corpuscles combines partly with the oxygen and partly with the carbon 

 monoxide, the final proportions (which can be easily and accurately deter- 

 mined) depending, in accordance with the laws of mass-action, on the relative 

 partial pressures of the oxygen and carbon monoxide, and on a constant. 

 Hence, if the final proportions, the constant, and the partial pressure of the 

 carbon monoxide avQ, known, the partial pressure of the oxygen can be 

 accurately deduced. By supplying to an animal air containing a fixed 

 proportion of carbon monoxide, until the final saturation of its htemoglobin 

 with carbon monoxide is reached, the partial pressure of oxygen in its 

 arterial blood can 1)e calculated on the same principle. If the arterial oxygen 

 pressure is greater than that of the alveolar air the final saturation of the 

 hfcmoglobin with carbon monoxide will be less than that of blood saturated 



* A comprehensive account of this controversy is given by Bohr in Nagel's ' Handbuch 

 der Physiologie,' vol. 1, p. 142, 1905. 



t ' Skand. Archiv fiir Physiologic,' vol. 23, pp. 17!)— 278, 1910. 



