ACIDOSIS 



43 



direction when the CO is decreased. If the CO o in the blood were not the same dur- 

 ing centrifuging as it is in the body, the separate plasma would not contain the same 

 amount of alkali i. e., its reserve alkalinity would be altered. Although theoretically, 

 therefore, centrifuging should be performed in an atmosphere containing the same 

 partial pressure of COs as exists in the body (i. e., the alveolar air) (see page 361), 

 this has been found impracticable for general use, and is unnecessary if loss of CO, 

 from the specimen of blood is prevented by allowing it to flow into the syringe very 

 slowly (without any suction). It is mixed in the syringe with powdered (neutral) 

 potassium oxalate (enough to make a 1 per cent solution with the blood), and imme- 

 diately delivered into a centrifuge tube under paraffin oil, which by floating on its 

 surface serves. to diminish free diffusion of CO 2 to> the 'outside air (even though such 

 oils dissolve more CO than water). To mix the blood with the oxalate, the syringe 

 should be moved backward and forward several times, but it must not be shaken. 



After centrifuging, ab'out 3 c.c. of plasma are removed and saturated with CO at 

 the same tension as in alveolar air (i. e., 5.5 per cent). This is done by placing the 

 plasma in a separating funnel of 300 c.c. capacity, laying the funnel on its side and 

 displacing the air in it by alveolar air secured by quickly making as deep an inspira- 



Fig. 10. Diagram of apparatus for saturating blood or plasma with expired air. The glass 

 beads in the bottle condense excess of moisture. The separating funnel, as soon as it has been 

 filled with expired air, should be closed by a stopper and the stopcock turned off. It is then 

 rotated so that the blood forms a film on its walls. 



tion as possible through the tube and bottle containing glass beads (Big. 10). The 

 glass beads remove excess of water vapor from the air. The funnel must be restop- 

 percd before the end of the expiration, so that no outside air enters. It is then ro- 

 tated, for about two minutes, in such a way that the plasma forms a film on its walls. 

 If it is necessary to postpone the saturating of the plasma, this should me pipetted off 

 from the corpuscles and preserved in hard glass test tubes coated with paraffin. From 

 ordinary glass enough alkali is soon dissolved out to vitiate the results. After satura- 

 tion of the plasma with C0 2 , the funnel is placed in the upright position and the 

 plasma allowed to collect in the narrow portion, after which 1 c.c. is removed with 

 an accurate pipette and analyzed for CO,. 



The analysis may be done by using either the Van Slyke or the ITaldanc-Barcroft 

 apparatus. The Van Slylcc method is as follows: 



The apparatus is filled to the top of the graduated tube with mercury (Fig. 11) 

 by raising the mercury reservoir F, care being taken that D and E are also filled. 

 One c.c. of the CO -saturated plasma is then delivered into A (which has been rinsed 

 out with CO -free ammonia water), and the stopcock I turned so that by cautiously 

 lowering the level of the reservoir F, the plasma runs into E (but no trace of air). 



