100 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



bottle is raised until it is above the level of the mercury in the burette by 

 3^3 of the column of laked blood.) 



5. With a negative pressure of several centimeters allow 2 cc. of 1.0 N 

 NaOH to run in and absorb the CO2 that has been liberated. 



6. Wait one minute for drainage and read again the gas volume. 



7. Repeat process 5 with 1 cc. of the NaOH until two check readings 

 are obtained. Draw down 1 cc, shake, then take reading. 



8. Wash the burette with distilled water. 



The difference between the first and second readings is the volume of 

 CO2 in 1 cc. of blood at the room temperature and the existing barometric 

 pressure. To correct to standard conditions of 0° and 760 mm. barometric 

 pressure, multiply by a factor obtained from Table 2 on p. 112which takes 

 account not only of the effect of temperature and barometric pressure 

 upon the gas volume but also corrects for the aqueous vapor present and for 

 a small amount of CO2 which remains unextracted or which is reabsorbed 

 by the solutions during the analysis. Cf. Van Slyke and Stadie, J. Biol. 

 Chem., 49: 1, 1921. 



The determination should be repeated several times with the same gas 

 mixture until reasonable checks are obtained. Then repeat, using two 

 other pressures of CO2. Plot the results with volumes per cent of CO2 as 

 ordinates and CO2 pressures as abscissae. Draw a smooth curve from the 

 origin and through the points as determined. Cf. L. J. Henderson, 

 "Blood," p. 78. Text p. 414. 



2. Calculation of the CO2 in Solution and in Chemical Combination. — 

 The volume of CO2 dissolved by 100 cc. of blood at a temperature of 38°C. 

 and at any partial pressure of CO2 (p.p. CO2) is given by the calculation: 



100 X 0.511 X ^'^-j^Q ^ or 0.0672 X p.p. CO2 (0.511 being the coeffi- 

 cient of solubility of CO2 in blood). This represents CO2 as a dissolved 

 gas and as carbonic acid. The remainder is present combined with base. 

 Calculate the proportion of CO2 in solution and in chemical combination 

 with base at each of the pressures determined above. Draw a line on your 

 graph indicating the volume per cent of CO2 in solution at various 

 pressures. Text p. 414. 



3. Calculation of the pH of the Blood. — This may be calculated as 

 follows : 



(Vol. % CO2 combined with base) 

 pH = 6.1 - log (Vol. % CO2 in solution) 



Estimate the pH of the blood at each of the pressures measured above. 

 Plot a curve relating the pH and the CO2 pressure. What is the pH at the 

 pressure of CO2 in arterial blood (40 mm.)? in venous blood (about 

 50 mm.)? 



