GENERAL PROPERTIES: THE CORPUSCLES. 419 



reaction, since it acts to change some of the disodium phosphate to 

 monosodium phosphate, and thus simply alters the ratio between 

 the concentrations of the two salts to an extent which does not influ- 

 ence the reaction. The concentration of bicarbonate of sodium 

 and carbonic acid in the blood is especially important in preserving 

 the weak alkalinity characteristic of the blood. Here again it 

 is the ratio of the carbonic acid to the bicarbonate of sodium 

 which controls the hyrogen-ion concentration, and experiments 

 have shown that this ratio may be varied within considerable limits 

 without materially influencing the reaction. If acid is added some 

 of the bicarbonate is broken up and carbonic acid is liberated; if 

 alkali is added some of the carbonic acid is changed over to bicar- 

 bonate. In the normal processes of the body there is a constant 

 output of acids which would tend to change the reaction of the 

 body liquids were it not for the protection afforded, first, by the 

 buffer action of the bicarbonate and phosphates of the blood, and, 

 second, by the action of the lungs in eliminating an excess of C02 

 and of the kidneys in excreting an excess of acid salts. 



TT f*<(~\ 1 



The ratio of carbonic acid to sodium bicarbonate, AT tr^A > * s given as ^ 



for arterial blood.* This ratio is obtained in this way: In the normal en- 

 vironment. of the tissues, that is to say, in an atmosphere containing 5.5 per 

 cent. CO 2 , the amount of CO 2 chemically bound as sodium bicarbonate is found 

 to be 60 volume per cent. Addition of excess of acid to 100 c.c. of blood liber- 

 ates 60 c.c. of CO 2 . The CO 2 contained in solution in the plasmas as H 2 CO 3 is 

 estimated from the absorption coefficient of CO 2 , namely, 0.54. Since the 

 blood is in an atmosphere of only 5.5 per cent. CO 2 the amount absorbed for a 

 unit volume will be 0.54 X 0.055 or 0.03, that is, 3 volumes for each 100 volumes 



TT OO ^ 1 



of blood. The ratio * t^Jl is equal then to ^ or JT-. If acids are added to 

 JN axlv^Us oU z(J 



the blood, as, for example, in muscular exercise, the denominatior will be dimin- 

 ished and the reaction will tend to become more acid, but this change stimu- 

 lates the respiratory center and causes an increased respiratory activity. 

 which thereby diminishes the numerator and restores the ratio to its normal 

 value. In this way the reaction of the blood is kept very constant through 

 wide changes in physiological activity. 



Acidosis. The actual reaction of the blood, as stated above, 

 does not vary much even under markedly pathological conditions. 

 but the amount of fixed acids added to the blood as a result of 

 the processes of metabolism may vary widely and may be greatly 

 increased under certain pathological conditions, diabetes for ex- 

 ample. While such an increase in the acids added to the blood 

 may not change its actual reaction perceptibly, owing to the pro- 

 tective mechanisms described, it will tend, of course, to reduce the 

 amount of protective sodium bicarbonate, since these acids will 

 combine with the sodium and drive off the CO 2 , which is then re- 

 moved by the lungs. The result in such cases is a diminution in 

 _* Van Slyke and Cullen, "Journal of Biological Chemistry," 1917, 30, 289. 



