SECRETION AND ABSORPTION OF GAS, ETC. 245 



These experiments and particularly No. 12, certainly 

 seem to afford most conclusive evidence that diffusion 

 alone does not in all cases explain the interchange of gases 

 in the lungs. On the other hand, it may be objected that 

 the number of results clearly inconsistent with the diffusion 

 theory is still too small to exclude all possibility of mistakes. 



It is evident from the irregularity of the results obtained 

 that the aerotonometer method, even in the improved form 

 given to it by Bohr and Fredericq, presents many serious 

 difficulties in practice, one of the chief of which is due to 

 the fact that the animal is not under normal conditions 

 during the experiment. Apart from these difficulties there 

 are certain sources of fallacy which may or may not be 

 serious, but which have not hitherto been excluded in 

 connection with the method itself. In the first place it is 

 by no means certain that the whole of the blood passing- 

 through the lungs is really aerated. Geppert and Zuntz, 1 

 whose authority on such a point cannot be questioned, bring 

 forward very definite reasons for concluding that, during 

 ordinary respiration at least, a small portion of the blood- 

 stream through the lungs probably escapes aeration. If 

 this be the case the results obtained by the aerotonometer 

 may not be the gas tensions of the aerated blood from the 

 lungs, but of a mixture of this blood with some venous 

 blood. Such an admixture as Geppert and Zuntz believe 

 to occur would not very appreciably raise the carbonic-acid 

 tension of the blood in an artery, but might easily reduce 

 the oxygen tension to half. From experiments by Hiifner 

 with haemoglobin solutions and fresh blood outside the 



1 Pfiiiger's Archiv, vol. xlii., p. 229, 1888. 



