CHANGES IN AIR AND BLOOD IN RESPIRATION. 



675 



In Fig. 275a a dissociation curve for human blood is given in 

 which this factor was considered. The curve shows also, in the 

 thickness of the line, the individual variations that may be ex- 

 pected in the bloods of normal persons. For example, at an 

 oxygen pressure of 40 mms. the percentage saturation of the hemo- 

 globin for oxygen varies between 70 and 78 or 79. For a blood 



20 



30 40 



90 100 



Fig. 275 a. — The dissociation curve for human blood. The thickness of the curve indicates 

 the limits within which the curve may fall for normal persons. The figures along the abscissa 

 indicate the pressure of oxygen in mms. of mercury; those along the ordinate indicate the per- 

 centage saturation of the hemoglobin with oxygen. (From Barcroft, "The Respiratorj- Func- 

 tion of the Blood." By permission of University Press, Cambridge, England, Publishers.) 



that falls within the limits indicated by the curve Barcroft* pro- 

 poses the designation mesectic. Bloods which at any given pres- 

 sure, below saturation, take up a larger percentage of oxygen 

 (higher curve) may be called pleonectic, while those which under 

 the same conditions are less saturated than normal (lower curve) 

 are meionectic. 



Condition of the Carbon Dioxid in the Blood. — The condition 

 in which the carbon dioxid is held in the blood is not entirely 

 understood. It has long been recognized that a certain small 

 percentage is held in simple physical solution in the plasma and 

 in the corpuscles, and that a certain additional amount, much 

 larger than the preceding, is in solution in the plasma in the form 

 of sodium bicarbonate, HNaCOs. From the results of gas-analyses 

 it is known that each 100 c.c. of blood contains, in round numbers, 

 from 40 to 45 c.c. of CO2, depending on whether it is arterial or 

 * Barcroft, "The Respiratory Function of the Blood," 1914. 



