Hydrogen Ion in Blood 



363 



Blood is drawn without stasis in a narrow 5 c.c. Luer glass 

 syringe containing sufficient mineral oil to fill any air spaces, 

 and is at once delivered into a centrifuge tube of special design 

 under oil. This tube is made of Pyrex glass and has at the 

 bottom a bulb of 2 c.c. capacity (30 mm. in length with an inter- 

 nal diameter of 11 mm. and a neck of 4 mm.). Tubes with 

 bulbs of 1 and 5 c.c. capacity have also been used, the latter being 

 employed when a simultaneous estimation of the C0 2 content 

 of the plasma is to be made. One drop of neutral 20 per cent, 

 potassium oxalate is dried in the tube, after which three drops 

 of mineral oil are added. In transferring the blood from the 

 syringe to the centrifuge tube, the point of the needle is placed 

 under the oil and sufficient blood delivered to bring the oil into 

 the neck of the bulb. With the slight pressure exerted the blood 

 readily takes up the oxalate and does not clot. The tube is cen- 

 trifuged at moderate speed for about two minutes to separate 

 the plasma. 



As a check on the possible influence of the oil on the P H under 

 these conditions, specimens of blood plasma, saturated with 

 C0 2 at alveolar tension, have been similarly centrifuged under 

 mineral oil. P H estimations were made both before and after 

 the centrifuging, but disclosed no appreciable change in the P H . 



A 0.9 per cent, solution of sodium chloride in C0 2 free 

 water, to which has been added 10 c.c. of 0.02 per cent, phenol 

 red solution for each 100 c.c. is adjusted to a P H of 7.4 with 

 sodium hydroxide and then kept under oil in a paraffin lined 

 bottle. Two c.c of this solution are allowed to flow into the 

 cup of the bicolorimeter under oil. A small portion of the 

 separated plasma is now drawn into a 0.5 c.c. tuberculin syringe 

 graduated in 0.01 c.c. (the point of the needle can best be cut 

 off), the air spaces of which are filled with mineral oil. One 

 tenth c.c. of the plasma is immediately discharged into the saline 

 solution in the cup. This solution is stirred with a small glass 

 rod and is then ready for color comparison. 



For this purpose the two wedges of the colorimeter are filled 

 with Sorensen's buffer phosphate solutions, containing 2 c.c. 

 of 0.02 per cent, phenol red for 20 c.c. of phosphate solution, 

 the front wedge having a P H value of 8.0 and the second wedge 

 of 6.8. The wedges are calibrated, as already described, 2 with 

 a series of buffer phosphates ranging from P H 7.0 to 7.8 and 

 differing by 0.1 P H - The readings made with the wedge con- 



