7 ?8 CHEM2STR Y OF RESPIRA TION. 



the tension of that gas varied between 0'9 and 57'8 mm. In the majority 

 of the experiments the air of the trachea contained carbon dioxide with 

 a higher tension than that of the gas in the blood. From these results 

 Bohr concluded that the exchange of gases between the air of the alveoli 

 and the blood in the lungs could not be accounted for by diffusion alone, 

 and he suggested that the tissues of the lungs played an active part in 

 the absorption of oxygen and in the excretion of carbon dioxide. 



These results are so opposed to those obtained by Pniiger and his 

 pupils, that they naturally are subject to considerable criticism. 1 In the 

 first place, it is to be noted that the respiratory quotients obtained by 

 Bohr during his experiments show values varying from 0'54 to 1*01, 

 results which suggest imperfect and irregular ventilation of the lungs. 

 Hiifner 2 contests Bohr's results, and suggests that the irregularities in 

 the results are due to a want of equilibrium in the tension of gases in 

 the blood and in the air of the hsemataerometer. He finds that equilibrium 

 only obtains after several minutes and vigorous shaking of the blood in 

 the apparatus. Similar objections have been made by Fredericq, 3 who 

 obtained, for the tension of oxygen in the peptonised arterial blood of the 

 dog, results always lower than the partial pressure of oxygen in the air 

 of the alveoli. Further, the results obtained by Fredericq for the carbon 

 dioxide agree with those given by Pflliger and his pupils. 



The following values are given by Fredericq 4 for the tension of oxygen 

 and of carbon dioxide in percentages of an atmosphere. 



Dog. 



External Air. Air of Alveoli. Arterial Blood. Tissues. 



Tension of oxygen . . 20'95 > 18 > 14 > 



External Air. Air of Alveoli. Venous Blood. Tissues. 



Tension of carbon dioxide . 0'03 < 2'8 < 3'81-5'4 < 5-9 



Quite recently Haldane and Lorrain Smith 5 have studied the tension of 

 oxygen in the arterial blood of man by a new method, which, they maintain, 

 avoids the probable sources of fallacy in the aerotonometer. In this new 

 method the tension of oxygen in the arterial blood is calculated from the 

 percentage of carbon monoxide breathed by the subject of the experiment, and 

 from the final saturation of liis blood with carbon monoxide. The results give, 

 for the oxygen tension of human arterial blood, a value of 26 '2 per cent, of an 

 atmosphere, or 200 mm. of mercury. This value is about twice as high as that 

 of the oxygen in the pulmonary alveoli, and if it be correct, it follows that 

 diffusion alone does not explain the absorption of oxygen by the blood in the 

 lungs. Haldane and Lorrain Smith discuss some of the possible sources of 

 error in their method, such as the estimation of the saturation of the blood 

 with carbon monoxide, the dissociation of carboxyhsemoglobin, the effect of 

 dilution of the haemoglobin, and the excretion or oxidation of carbon monoxide ; 

 but the test experiments which they made confirm them in their opinion of its 

 accuracy. 



Before, however, these results are accepted, further experiments are needed 

 to test the method, for it is impossible with our present knowledge to judge 



1 See also criticism by Zuntz, Fortschr. d. Med., Berlin, 1890, Bd. viii. S. 856. 



2 Arch. f. PhysioL, Leipzig, 1890, S. 10. 



3 CentralU.f. PhysioL, Leipzig u. Wien, 1893, S. 33. 



4 Fredericq et Nuel, "Elements de physiologic humaine," Gand, 1893, pp. 156-158. 



5 Journ. PhysioL, Cambridge and London, 1896, vol. xx. p. 497. 



