242 SCIENCE PROGRESS. 



attention was paid to the oxygen tension of the blood. The 

 value of 3 to 4 per cent, obtained by Strassburg for the 

 arterial oxygen tension was only minimal. In a later series 

 of experiments Herter 1 obtained a much higher value, 10*4 

 per cent., but even this was only minimal. 



The subject of the cause of gaseous exchange between 

 the blood and the air of the lungs was next taken up by 

 Bohr.-' The general principle of his apparatus was the 

 same as that of Pfliiger's aerotonometer, but the blood was 

 rendered incoagulable by a previous injection into the circu- 

 lation of leech extract or " peptone," and could thus be 

 allowed to flow continuously through the vessel containing 

 the gas mixture and back to the animal. The object of 

 this arrangement was to make it possible to obtain com- 

 plete equilibrium between the tensions of oxygen and car- 

 bonic acid in the gas mixture and in the blood. During 

 the experiments the amount of air per inspiration and the 

 average composition of the expired air was determined by 

 means of a special apparatus. The volume of the dead 

 space formed by the contents of the tracheal cannula and 

 trachea itself was also measured, so that it was possible to 

 estimate the composition of the expired air at the bifurca- 

 tion of the trachea. From his experiments Bohr concluded 

 that the oxygen tension of arterial blood is frequently 

 above, and the carbonic-acid tension frequently below, 

 that of the expired air ; and he draws the inference that 

 the lungs are capable of actively secreting oxygen inwards 

 and carbonic acid outwards. 



Still more recently the subject was again taken up by 

 Fredericq, 3 whose experiments were made on the same 

 general principles, although he did not determine the com- 

 position of the expired air. His experiments showed dis- 

 tinctly that the oxygen tension of the blood from an artery 

 varied from about 8 to 14 per cent, of an atmosphere, while 

 the carbonic-acid tension varied from 1 "4 to 4 per cent. 

 The oxygen tensions found by Fredericq were thus con- 



1 Zeitschrijt fiir physiologische Chemie, vol. iii., p. 98. 



2 Skatid. Archiv filr Physiologic, vol. ii., p. 236, 1891. 

 s Archives de Biologie, 1896, p. . 



