ACIDOSIS 79 



preciable loss of CO 2 for an hour or more. If the blood is kept longer, 

 or is agitated, as in centrifugation, paraffin oil is insufficient protection. 

 A layer of solid paraffin (melting point 40-45) may be used, or the tube 

 may be filled with blood entirely to the stopper, so that no air space is left. 



Van Slyke and Cullen (1917) used the precaution of saturating plas- 

 ma immediately before analysis with CO 2 at normal alveolar tension, in 

 order to prevent errors from escape of CO 2 during the period between 

 centrifugation and analysis. With the precautions for handling the 

 plasma and the mode of calculation below outlined, however, such resatura- 

 tion becomes unnecessary. 



Gasometric Determination of Whole Blood or Plasma Bicarbonate. 

 In either the whole blood or plasma the total CO 2 may be determined gaso- 

 metrically and the portion in the form of BHCO 3 , which is normally 

 about 95 per cent of the total, may be estimated from the pH. 



For determination of the total CO 2 Haldane (1920) adds acid to the 

 blood in a closed vessel connected with a sensitive manometer, and estimates 

 from the rise in pressure the amount of CO 2 set free. Y. Henderson 

 (1917) similarly adds acid to the blood in a relatively large closed vessel, 

 but measures the CO 2 evolved by running the air-CO 2 mixture from 

 the vessel into a gas burette, where the CO 2 is determined by analysis. 



Van Slyke (1917), in a method later refined by Van Slyke and Stadie 

 (1921), adds acid to the blood in a 50 c.c. pipette provided with stopcocks 

 at both ends. The entire space in the pipette, except that occupied by the 

 blood and acid, is filled with mercury, and the lower end of the pipette 

 is connected with a leveling bulb. By lowering the latter the mercury 

 is drawn out of the pipette, and a Toricellian vacuum obtained in it. 

 The escape of CO 2 into the vacuum is so rapid that it is complete in about 

 30 seconds. The mercury is then readmitted and the volume of CO 2 

 is read in the upper stem of the pipette, which is calibrated for the 

 purpose. 



Each of the above three methods may be used with 1 c.c. or less of 

 blood or plasma, and each has given satisfactory results in the hands 

 both of its originator and of other investigators. 



From the total CO 2 content determined by any of these methods the 

 BHCO 3 may be calculated by Table I. 



The table is computed from the equation pH = pK^ -f- log 



BHCO 3 



H 2 C0 3 ' 

 pKi having the value 6.15 for whole blood, 6.10 for plasma. Substituting 



R for the ratio ^^ , we have log R = pH pK x and 

 100 BHCO, 



BHCoH.00 



