BLOOD 



495 



is raised tlie dissociation curve is lowered v., and if the 

 temperature is lowered the curve is raised i., ii., iii. 



'2.nd. The H ion concentration of the blood. — This, as 

 already shown (p. 481), is controlled by the sodium bicar- 

 bonate of the plasma, and is chiefly determined by the 

 amount of dissociated H2CO3 in the blood. Any increase 

 of the C„ alters the form of the curve, tending to bring 

 about dissociation of HbOo at higher pressures, as is shown 

 in fig. 202. 



Fig. 202. — To show the effect of the tension of COo in the blood upon the 

 giving off of oxygen. The pressures of oxygen are given as the abscissse 

 in mm. Hg, and the saturation of the htenioglobin as the ordinates. Note 

 the marked difference at 20 mm. Hg of oxygen with 5 and with 40 

 mm. Hg pressure of C02- 



In fact, the CO., of the blood plays a most important part 

 in setting free the Og for the tissues, since it raises the C^ of 

 the blood. 



3'/yL The presence of electrolytes also lowers the curve. 



B. The Carbon Dioxide in the Blood. 



The carriage of CO., in the blood has already been dealt 

 with. It has been shown that it exists to a large extent as 

 NaHCOs and to a small extent in solution (p. 481). 



By subjecting blood to different pressures of COj, it is 

 found that the amount carried practically varies directly 



