THE CONTROL OF THE RESPIRATION 



339 



junction of the thistle-shaped bulb and the graduated tube. As the blood 

 is allowed to enter through the inflow tube, it is ejected in a fine stream 

 around the bubble of air, which moves about in the stream. The blood 

 displaces the saline out of the bulb into the side tube. After the bub- 

 ble has been subjected to the influence of the blood for some minutes, 

 the gases in it come into perfect equilibrium with those in the blood. 

 The percentage of 2 and C0 2 in the bubble will therefore correspond 

 to the tension of these gases in the blood. The analysis is effected by 

 drawing the bubble into the graduated tube by means of the syringe, 



Fig. 122. 



1 



rig. 123. 



Fig. 122. The gas analysis pipette for the microtonometer shown in Fig. 123. For description 

 see context. (From A. Krogh.) 



Fig. 123. Microtonometer, to be inserted into a blood vessel. The small circle represents the 

 bubole of air. For further description see context. (From A. Krogh.) 



measuring its capacity, transferring it into a bulb containing KOH, 

 which absorbs the C0 2 , then taking it back into the capillary tube and 

 again measuring. The shrinkage obviously corresponds to the amount 

 of C0 2 . The bubble is then transferred into potassium pyrogallate solu- 

 tion, where the 2 is absorbed.* 



The Tension of C0 2 and 2 in Alveolar Air, Having seen how we 

 may determine the tension of the gases in blood, we must now consider 



*Since the above was written, a more efficient tonometer devised by the late T. G. Brodie has 

 been described by O'Sullivan (Am. Jour. Physiol., Sept., 1918). 



