BETWEEN THE BLOOD AND ALVEOLAR AlR 547 



of the inspired air, after allowance has been made for dilution of 

 the latter by aqueous vapour. Therefore from a knowledge of 

 the percentage of carbonic oxide breathed by the subject of the 

 experiment, and of the final saturation of his blood with carbonic 

 oxide, the oxygen tension of his arterial blood may be calculated." 

 (Haldane and Lorrain Smith.) 



With this method numerous experiments have been made by 

 Haldane and Lorrain Smith ( 23 ) upon the partial pressure of oxygen 

 in the arterial blood of man and animals. The average results 

 for the normal condition are shown in the following table. 



If the normal pressure of oxygen in the alveolar air of these 

 animals be assumed to be 13 to 14 per cent, of an atmosphere, 

 diffusion alone cannot explain the absorption of oxygen, for the 

 pressure of the gas in the arterial blood is higher in every case. 

 The influence of various conditions upon the absorption was also 

 determined. A fall in the internal temperature of the body by 

 exposure to cold reduced the pressure of oxygen in the arterial 

 blood of a mouse from 22-6 to 15- 1 per cent, of an atmosphere. 

 An increase in the percentage of oxygen in the alveolar air, when 

 the animal breathed mixtures rich in oxygen, caused an almost 

 proportional increase in the pressure of oxygen in the arterial 

 blood ; on the other hand, want of oxygen, whether produced by 

 poisoning with carbon monoxide, diminution in the percentage of 

 oxygen in the inspired air, or diminution in atmospheric pressure, 

 caused a fall in the pressure of the oxygen in the arterial blood, but 

 a marked increase in the relative excess of the pressure of oxygen 

 in the blood over that in the alveolar air. Thus want of oxygen 

 acted as a stimulus to the absorption of the gas. 



