VAN SLYKE'S CO 2 APPARATUS 419 



dropping bottles with ground in pipettes and rubber teats containing 

 (a) 5 per cent. H 2 S0 4 , (b) 1 per cent, carbonate-free NH 3 water, (c) caprylic 

 alcohol and (d) distilled water. The carbonate-free ammonia is prepared 

 by adding a small amount of sat. barium hydrate solution to ordinary 

 ammonia solution. The barium carbonate is filtered off, and the excess 

 of barium remaining is precipitated with a little (NH 4 ) 2 S0 4 . 



(2) Plasma. An ordinary centrifuge tube is fitted out with rubber cork 

 and glass tubes just like a wash-bottle. The longer tube bears at its upper 

 end a hypodermic needle. The whole apparatus glass, tubes and needle- 

 is washed out with a saturated solution of neutral potassium oxalate. 

 (Van Slyke and Cullen point out that it is desirable that the subject should 

 avoid vigorous muscular exertion for at least an hour before the blood is 

 drawn. It is also best to avoid stasis, or when stasis is unavoidable the 

 ligature should be released as soon as the vein is entered. In this case, 

 the first sample of blood should be neglected.) The blood should run into 

 the tube without suction. By a gentle rotary motion, mix the blood with the 

 finely crystallised oxalate left adhering to the walls of the vessel, and centri- 

 fuge at once. The plasma is then transferred to sampling tubes (Fig. 80), 



SAMPLING TUBE. 



FIG. 80. Alveolar Air Collecting Tube. 



3-4 c.c. of plasma to each tube. These tubes (300 c.c.), or separating 

 funnels of the same capacity, are filled with alveolar air (of the subject, if 

 possible). This may be done by holding the tube horizontally, opening 

 both taps and, without inspiring more deeply than normal, expire as quickly 

 and as completely as possible through the tube, closing the further tap 

 just before the expiration is finished. A bottle containing large glass 

 beads must be interposed between mouth and funnel in order to prevent 

 dilution of the plasma by condensation of vapour from the breath. With 

 both taps closed, the funnel is rotated (not shaken) so that the plasma 

 forms a thin layer over the walls, and so readily comes into equilibrium as 

 regards C0 2 tension with the alveolar air. 



(3) Procedure. The apparatus is entirely filled with mercury, including 

 the two capillaries ( and stem of b) at the top. The cup b is washed with 

 C0 2 -free NH 3 . 1 c.c. of plasma is run into the cup from an Ostwald-Folin 

 pipette, keeping the tip of the pipette immersed in the fluid. Placing the 

 mercury reservoir in the second ring (Fig. 79) and with cock/ open to d, 

 open e and admit the plasma to the pipette, leaving sufficient in b to fill the 

 capillary. Wash the cup twice into the pipette using about 0-5 c.c. of 

 water each time, adding a very small quantity of caprylic acid to the 

 second wash water. Finally run in 0-5 c.c. of 5 per cent. H 2 S0 4 and seal 

 the capillary with mercury. The fluid must come to the 2-5 c.c. mark. 

 Wash out the cup with water and then with carbonate-free ammonia till 

 acid-free. The mercury bulb is now taken to a position (about 80 cm. 

 below the second ring) so that a Torricellian vacuum is formed in the gas 

 pipette. Allow the mercury to run down almost to (but not below) the 

 B.B. 27* 



