222 



RESPIRATION 



About fifteen years later the aerotonometer was greatly im- 

 proved by Krogh, who was then Bohr's assistant. He very greatly 

 diminished the volume of air exposed to the blood in the aeroto- 

 nometer, thus rendering it far quicker in its action ; and ultimately 

 he succeeded in working with a single bubble of air, round which a 

 stream of blood could play, the bubble being afterwards analyzed 

 with the help of a graduated capillary tube into which it could be 

 sucked up and measured before and after its CO2 and oxygen 

 had been removed by suitable reagents. 



Figure 66. 

 Krogh's micro-aerotonometer, showing inlet and outlet 

 for blood, lower part of measuring tube, and air bubble. 



Before his death Bohr published some experiments made with 

 Krogh's aerotonometer, and apparently showing distinctly that 

 the pressure of CO2 in the venous blood could be less than in the 

 expired air, although CO2 was being given off in the lungs ; and 

 that the arterial CO2 pressure could also be less than that of the 

 expired air. Krogh himself, however, took the view that there 

 were errors in these experiments, and published, along with M. 

 Krogh, the results of a careful series of experiments on animals 

 under conditions which were much more nearly normal than in 

 any previous experiments.^^ The arterial oxygen pressures were 



" A. and M. Krogh, Skand. Arch. /. Physiol., XXXII, p. 179, 1910. 



