384 



RESPIRATION. 



The tension of CO 2 in the blood is as follows : In arterial 

 blood 21.28 mm., and in venous blood 41.04 mm. CO 2 exists in 

 venous blood in solution to the amount of about 5 per cent.; in 

 loose chemical combination, 75 to 85 per cent.; and in firm chemi- 

 cal combination, 10 to 20 per cent. or about 45 volume per cent, 

 in all. The CO 2 is in solution in the plasma, in combination with 

 globulin and alkali, and with sodium in the form of carbonates 

 and bicarbonates. About one-third of the carbon dioxid of the 



FIG. 212. Kemp's gas pump. (For detailed description see American Text-BooTc of 

 Physiology, vol. i., p. 420.) 



blood exists in the blood-corpuscles, both white and red, but prin- 

 cipally in the latter, where it is in combination with the alkaline 

 phosphates, with globulin and hemoglobin. 



We have seen that by various forces the oxygen in the outside 

 air reaches the alveoli, while in turn the carbon dioxid in the 

 latter situation reaches the exterior ; we have now to consider how 

 the interchange between the CO 2 in the blood and the O in the 

 alveoli is effected. We have learned that the tension of the O 



