106 RESPIRATION 



with air, and as a consequence nitrogen diffuses from the potash 

 solution into the gas mixture, while oxygen diffuses into the 

 potash solution. The consequence is that the residue of nitrogen 

 found in the gas after the oxygen has been absorbed is greater 

 than was originally present in the gas. This source of error is 

 absent if little or no oxygen is present in the gas pumped off from 

 the blood. We can thus explain why no extra nitrogen has been 

 found in reduced blood. 



Bayliss 4 contends that the bicarbonate and the plasma proteins 

 present in blood play no part in the physiological carriage of 

 CO 2 between the tissues and the lungs, and that haemoglobin is 

 alone concerned in the carriage, since it does not, under actual 

 physiological conditions, compete as an acid with CO 2 for the 

 alkali available in the blood. The experiments cited in support of 

 this conclusion seem to me quite unconvincing; and if it were cor- 

 rect we should expect to find that blood saturated at the alveolar 

 partial pressure with CO 2 would contain more combined CO 2 than 

 a solution of bicarbonate of the same strength in titratable alkali 

 as the blood. Actually, the blood, especially at body temperature, 

 contains far less combined CO 2 . It seems quite impossible to 

 reconcile Bayliss' theory with this fact ; and I cannot see how any 

 other theory than that given in the first part of this chapter is 

 capable of interpreting the facts as a whole. It may be that a small 

 amount of CO 2 is combined with free haemoglobin ; but it seems 

 evident that under physiological conditions haemoglobin and 

 other proteins act, for all practical purposes, simply as weak acids. 

 It is in virtue of this action, and the more powerful action of 

 oxyhaemoglobin than reduced haemoglobin as an acid, that blood 

 functions so efficiently as a physiological carrier of CO 2 . Campbell 

 and Poulton, who entirely disagree, and on substantially the same 

 grounds as I do, with the conclusions of Buckmaster and Bayliss, 

 have recently shown that an artificial mixture of dialysed cor- 

 puscles and dilute sodium bicarbonate solution takes up, within 

 physiological limits of CO 2 pressure, much less CO 2 than the 

 bicarbonate alone holds. 5 



For the sake of simplicity I did not discuss separately the 

 action of plasma and corpuscles in combining with CO 2 ; but much 

 attention has been given recently to this subject. Zuntz 6 pointed 

 out that when plasma or serum is separated from blood collected 



4 Bayliss, Journ. of Physiol., LIII, p. 162, 1919. 



5 Campbell and Poulton, Journ. of Physiol., LIV, p. 157, 1920. 



6 Zuntz, Hermann's H ' andbuch der Physiol., IV, 2, p. 77, 1882. 



