122 METHODS FOR THE ANALYSIS OF BLOOD 



Comparative determinations of the oxygen content of the 

 blood by the Barcroft-Haldane method using the Brodie apparatus 

 (5) and by this method gave the following results: 



Rarcroft-Haldane Method Gas Analysis Method 



16.2 16.3 



16.5 16.1 



The two methods are of approximately the same order of 

 accuracy. To one accustomed to the use of the gas analyzer, 

 but not in practice for the use of the Barcroft-Haldane method, 

 in its usual form, this modification is believed to be decidedly 

 the easier. 



The precision of the method may be increased, at least theo- 

 retically by filling the diffusion tube initially with nitrogen (from 

 the analyzer) instead of air, inserting the stopper under water, 

 and injecting the hypodermic syringe. But this refinement takes 

 time and requires extreme care to avoid admitting the least trace 

 of air. 



CO 2 DETERMINATION 



The CC>2 content of the blood is determined in exactly the same 

 manner and with the same tube, merely using the tartaric acid 

 solution instead of ferricyanide. (When the amount of gas in the 

 blood is very high it is advisable to use only half quantities of blood 

 and reagent; namely, 0.75 c.c. of blood, and 0.10 c.c. of tartaric 

 acid.) Owing to the solubility of CO2 it is necessary in the calcu- 

 lation of the results to .take into account that part of the gas which 

 remains in solution in the acidified, diluted blood. This correction 

 for any temperature may be obtained from Curve 1 in Fig. 8. 



A typical calculation of the results obtained is as follows: 



Volume of air at 18 C. (compressed) in diffusion tube 



before removing stopper = 10.9 c.c. (1) 



Volume of air (at atmospheric pressure) in diffusion 



tube after removing stopper =11.1 c.c. (2) 



Volume taken for analysis = 7.774 c.c. (3) 



Gas remaining after absorption of CO2 = 7.506 c.c. (4) 



CO 2 absorbed, i.e., (3) - (4) = 0.268 c.c. (5) 



(2) 

 Total CO 2 in air in tube, i.e., (5) X = 0.383 c.c. (6) 



