THE GASES OF THE BLOOD 



259 



in the amount of the pulmonary ventilation, which affect the partial 

 pressure of the carbon dioxide in the alveolar air and thus alter the 

 steepness of the slope of pressure between the two sides of the pul- 

 monary membrane. 



It is chiefly the enormous differences in the recorded oxygen 

 tensions of the arterial blood which excite surprise. To some ex- 

 tent, indeed, these also may depend upon differences in the partial 

 pressure of the oxygen in the alveoli, and it has been shown experi- 

 mentally (by the aerotono meter) that with increasing oxygen tension 

 of the inspired air the oxygen tension of the arterial blood increases 

 (Fredericq). Still, the differences which can possibly have existed 

 in the partial pressure of the oxygen in the alveoli in the various 

 series of observations can only to a small extent account for the 

 differences in the results. The main reason for the great range of 

 values lies unquestionably in the different experimental procedures 

 by which they were obtained. There is no doubt that in the earlier 

 observations with the aerotonometer (Strassburg) the oxygen of 

 the blood could not have come into equilibrium with the mixture 

 in the gas space, in which the oxygen pressure was at the beginning 

 much lower than that in the blood; the results are therefore too low. 

 The same is true for the oxygen tension of the venous blood, but as 

 this is in any case considerably smaller than that of the arterial 

 blood, the proportional error is not so great. The later experiments 

 (of Herter), given in the second line of the table, yield much higher 

 values, owing to improved technique, but the findings are still to be 

 regarded as minimal and not average results. At the other end of 



* The numbers in brackets are averages. 



