The acquisition of oxygen by the blood in the lung 185 



forget its close analogy to the glomerular function of the kidney. 

 The epithelium covering the latter organ is, in a general way, similar 

 to that covering the lung ; how vast is the mass of physiological 

 literature which tacitly assumes that if secretion can be proved in 

 the amphibian capsule of Bowman, it may be taken for granted in 

 the case of the primates. We do not wish to insist unduly upon the 

 inherent reasonableness of Bohr's point of view, but we regard his 

 position as at least more reasonable than that of the lecturer who in 

 one lecture denounces Bohr's view as extravagant, and in the next 

 teaches a doctrine of universal glomerular secretion on the basis of a 

 long series of well-established experiments on frogs. Neither Bohr, 

 nor any of his supporters, have ever gone so far as this ; their position 

 has always been that even granting secretion of oxygen in the cod 

 and other low forms, its existence in higher ones remains a matter to 

 be decided by experiment. 



About twenty years ago, it was therefore of the utmost importance 

 that some totally new method should be sought, which would decide 

 between the rival aerotonometricians. Such a method was devised 

 by Haldane (1) , and in his hands and those of his collaborators, Lorrain 

 Smith and Douglas, has played a very important part in the physio- 

 logical thought of the last two decades. 



The principle of the method may be summed up in a few words. 

 If haemoglobin be exposed to a mixture of oxygen and carbon 

 monoxide, the resulting quantities of oxy- and carboxy-haemoglobin 

 depend upon the relative pressures of oxygen and carbon monoxide. 

 In short there is a balanced action 



CO + O 2 Hb ^ COHb + O 2 . 



If therefore any three of the quantities involved are known, the 

 fourth can be calculated. Haldane administered CO in known 

 quantities, i.e. at a known pressure (for the pressure of CO in the 

 air was taken as the index of its concentration in the plasma) ; he 

 estimated the relative quantities of 2 Hb and COHb present, and 

 from these data calculated the pressure of oxygen in the blood. 



Before this could actually be done, however, a great deal of 

 ground had to be cleared ; in the first place a method of estimating 

 the relative proportions of oxy- and carboxy-haemoglobin had to be 

 devised ; in the second place the necessary data had to be accumu- 

 lated for determining what was the precise relationship of the four 

 substances in question in all possible cases in which equilibrium existed. 



