CHANGES IN AIR AND BLOOD IN RESPIRATION. 609 



claim that the tension of the oxygen in the arterial blood is higher than the 

 pressure of oxygen in the alveolar air, and Bohr has stated that the pressure 

 of CO 2 in the air in the trachea is higher than that in the venous blood. If 

 these facts were fully demonstrated they would show that the physical theory 

 outlined above is insufficient, and would indicate that the membranes con- 

 cerned take an active part in the passage of the gases, exerting possibly a 

 secretory activity. That the cells of these membranes might secrete the 

 gases is not at all impossible, but at present it seems to be unnecessary to 

 make such a supposition. The results obtained by the observers mentioned 

 in this paragraph have not been corroborated by the numerous other ob- 

 servers who have worked in the same field, and it seems probable that they 

 may be due to experimental errors. A well-known set of experiments that 

 strengthen this conclusion has been reported by Wolffberg and by Nussbaum * 

 and has since been repeated upon man. In these experiments one bron- 

 chus in a dog was completely blocked by a specially designed lung catheter, 

 so arranged as to occlude the bronchus and yet allow the observer to draw 

 off a specimen of the air at any time. In such an occluded lung the captured 

 air is in diffusion relations with the venous blood of the pulmonary artery, 

 and if these relations are maintained for a sufficient time an equilibrium 

 should be established on the physical theory, the tension of the gases hi the 

 occluded lungs becoming the same as in the venous blood. Such was found 

 to be the case. When at the end of the experiment air was drawn off and 

 analyzed it was found to contain 3.6 per cent, of CO 2 , while the tension of 

 the CO 2 in specimens of the venous blood taken from the right heart was 

 practically identical. If there is an active secretion of CO 2 from the lungs 

 one should have expected to obtain a higher tension in the carbon dioxid 

 of the alveolar air than in the venous blood. 



* " Archiv f. die gesammte Physiologic," 4, 465, 1871, and 7, 296, 1873. 



