CHAPTER V 

 The Blood as a Carrier of Carbon Dioxide. 



WE must now turn to the consideration of the blood as a carrier of 

 CO 2 . Mammalian arterial blood has usually been found to contain 

 about 40 or 50 volumes of CO 2 per 100 volumes of blood, while 

 venous blood from the right side of the heart contains several 

 volumes more. The following average results obtained with the 

 mercurial pump by Schoeffer 1 illustrate the difference between 

 venous and arterial dogs' blood, although much doubt must exist 

 as to whether the circulation and respiration were at normal rest- 

 ing values when the samples were taken. Much more reliable data 

 will be given for man in Chapter X. 



OXYGEN CO 2 



Arterial blood 19.2 39.5 



Venous blood from right heart 11.9 45.3 



Difference 7.3 5.8 



In man, as will be shown below, normal arterial blood contains 

 during rest about 53 volumes per cent of CO 2 if the blood is satu- 

 rated with CO 2 at the pressure (about 40 mm.) existing in average 

 alveolar air of adult men. As 100 volumes of blood, according to 

 Bohr's 2 calculation, take up in simple solution about 51 volumes 

 of CO 2 in presence of a pressure of one atmosphere of CO 2 at body 



temperature, they can only take up ~- x 51 = 2.7 volumes at the 



760 



normal alveolar pressure of 40 millimeters or 5.3 per cent of an 

 atmosphere. Hence only 2.7 volumes per cent of the CO 2 are in 

 simple solution, the other 50.3 volumes being in chemical combi- 

 nation. As will be shown below, the difference between the partial 

 pressures of CO 2 in human arterial and venous blood during rest 

 is only about 6 mm. or 0.8 per cent of an atmosphere. Hence the 

 physically dissolved CO 2 given off in the lungs is only 0.4 volumes 



1 Schoeffer, Sitz. ber. d. Wiener Acad., math. nat. cl., XLI, p. 589, 1860. 

 8 Bohr, Nagel's Handbuch der Physiol., II, p. 63, 1905. 



