BETWEEN THE BLOOD AND ALVEOLAR AIR 545 



It has already been shown that it is not true alveolar air. In 

 pathological cases of collapse of the lung, and in experiments upon 

 the production of artificial collapse, all the air in the portion of 

 the lung involved is absorbed in a few hours ; the lung-catheter 

 may also produce conditions too abnormal for experiments to 

 decide the question. 



Bohr constructed an improved aerotonometer, the haematsero- 

 meter, through which a constant and rapid stream of arterial 

 blood could be maintained. Dogs were used for the experiments, 

 the coagulation of the blood was prevented by the injection of 

 leech-extract or peptone, and the blood from an artery, after passing 

 through the hsemataerometer, passed back to the animal's body 

 through the peripheral end of the artery or the central end of a 

 vein. The composition of the expired air, as it passed the bifurca- 

 tion of the trachea, was determined by qualitative and quantitative 

 analyses of the expired air and direct measurement after the 

 death of the animal of the volume of the " dead space," which in 

 this case was the trachea and tracheal cannula. Bohr obtained 

 for the pressure of oxygen in arterial blood results as high as 101 

 to 144 mm. of mercury, and in nearly every case the pressure was 

 higher than that of the expired air at the bifurcation of the trachea, 

 and therefore higher still than that of the true alveolar air. The 

 absorption of oxygen in these cases could not be explained by 

 diffusion. For the pressure of carbon dioxide the results vary 

 greatly from 0-9 to 29-7 mm. ; in some cases, as shown in the 

 following table, they are much below the pressure in the air at 

 the bifurcation of the trachea, in other cases higher. 



From these results Bohr concludes that the absorption of 

 oxygen and the excretion of carbon dioxide are active secretory 



2 M 



