138 EXPERIMENTAL PHYSIOLOGY. 



THE C0 2 -COMBINING POWER OF THE ALKALINE 

 RESERVE OF THE BLOOD. 



After completing the estimations necessary for finding the per- 

 centage of oxy haemoglobin, in the experiments in which CC>2 is 

 present in the tonometer, it is of interest to determine the amount 

 of this gas with which the blood has combined. This will repre- 

 sent its ability to act as a buffer towards foreign acids. To perform 

 the estimation it is necessary, however, to measure accurately the 

 amount of blood which is removed from the tonometer to the blood 

 gas bottle. This can readily be done by attaching a 1 c.c. pipette 

 to the tubing of the tonometer (beyond clip 1), a few drops of blood 

 being allowed to escape from the pipette before delivering under 

 the ammonia solution in the bottle, and precautions being taken 

 not to remove any of the upper layers of blood that had been exposed 

 to full atmospheric pressure when the tonometer was opened. 

 This is ensured by removing the pipette from the tonometer before 

 all the blood has run out. 



To dislodge the CO2 from the blood, the stopper is removed 

 with the usual precautions and about 0.25 c.c. of a saturated solution 

 of tartaric acid placed in the small test tube. After closing and 

 allowing for temperature changes, the acid is shaken with the 

 mixture of blood and ferricyanide, and the CO2 thereby evolved, 

 measured by multiplying the displacement of the fluid in the 

 manometer by a figure (the constant of the apparatus) obtained by 

 a preliminary experiment in which a known amount of a standard 

 carbonate solution is similarlv treated. 



