92 RESPIRATION 



amount, as after forced breathing, or during excessive artificial 

 respiration, or other respiratory disturbances, CO 2 may easily be 

 given off by the lungs when there is no excess of venous over 

 alveolar CO 2 pressure, or even when the venous CO 2 pressure is 

 considerably lower than that of the alveolar air. For when the 

 blood reaches the lungs the process of oxygenation so reduces the 

 capacity of the blood for CO 2 that its CO 2 pressure is raised 

 above that of the air, and diffusion results. If the respiratory 

 quotient has fallen temporarily to a third or less of its normal 

 value, the thick line of Figure 26 will become vertical in the living 

 body, or incline to the left instead of to the right. It is merely 

 necessary to suspend the breathing for a very short time in order 

 to realize this condition. Only if air containing a large excess of 

 CO 2 is breathed, will CO 2 be absorbed backwards, and the thick 

 line pass downwards as well as to the left. 



Tlje discovery that oxygenation of the haemoglobin helps to 

 turn out CO 2 from blood gives us the key to the proper interpreta- 

 tion of the fact that, as was found by ourselves in human experi- 

 ments, and earlier by Werigo, 10 and by Bohr and Halberstadt, 11 

 more CO 2 is given off into the air of the lungs when oxygen is 

 present. Thus in Halberstadt's experiments it was found that if 

 one lung was ventilated with air, and the other with hydrogen, 

 the lung ventilated with air gave off nearly 50 per cent more CO 2 

 than the lung ventilated with hydrogen. This result is precisely 

 what would be expected in view of the facts just described; but 

 as Bohr was misled by the apparent results of his experiments 

 with blood outside the body, he wrongly attributed Halberstadt's 

 and Werigo's results to the supposed fact that in presence of air 

 there is a large formation of CO 2 in the lungs, owing to a process 

 of oxidation occurring there. As will be shown later, hardly any 

 formation of CO 2 occurs in the lungs. 



In a quite recent paper Parsons 12 has investigated mathemati- 

 cally the form of the absorption curve of blood for CO 2 on the 

 theory that the blood is a chemical system consisting of carbonic 

 acid and what may be regarded as one other free acid (consisting 

 of the proteins present) with a fixed concentration of available 

 alkali distributed between them. This fixed concentration he 

 estimated from blood-ash analyses and in other ways, to be about 

 4.5 x io~ 2 N. He found that the form of the curve given by calcula- 



10 Werigo, Pfliiger's Archiv., LI, p. 321, 1892. 



11 Bohr, Nagel's HancLb. der Physiol., I, p. 208. 

 13 Parsons, Journ. of PAysiol., LIII, p. 42, 1919. 



