CHAPTER XII 



THE ACQUISITION OF OXYGEN BY THE BLOOD IN THE LUNG 



WE have now arrived at the point at which it would be de- 

 sirable to apply our knowledge of the dissociation curve of blood 

 to the solution of a number of physiological problems, and to 

 give some complete history of the transportation of oxygen from 

 the lung to the tissue. Before doing this however we find that there 

 is a difficulty confronting us in the nature of the transition of gases 

 through the epithelium of the lung itself. The older physiologists 

 would freely have assumed that because the oxygen in the alveolar 

 air of the lung exercises a pressure of about 100 mm. of mercury, the 

 blood would be saturated with oxygen up to the point corresponding 

 with that pressure ; in other words, that the pressures of oxygen in 

 the lung and in the arterial blood would be approximately equal. 

 This assumption was based upon the work of the Bonn School of 

 physiologists. 



If I am to give a coherent account of the controversy which has 

 taken place between those who believe that oxygen is secreted by the 

 pulmonary epithelium and those who believe that it diffuses from the 

 alveoli into the blood, I must go a little further into the history of 

 the subject than I have been wont to do heretofore. 



The aerotonometer methods of the Bonn physiologists seemed to 

 have established the theory of diffusion in the lung on a satis- 

 factory basis when Bohr, using similar but not precisely the same 

 methods, found that there was 



(1) A greater pressure of oxygen in the arterial blood than in 

 the alveolar air. 



(2) A greater pressure of carbonic acid in the alveolar air than 

 in the arterial blood : 



neither of which phenomena could be accounted for by simple 



