ACIDOSIS 



43 



incurred will become greatly aggravated if venous stasis has been pro- 

 duced in drawing the specimen for analysis. But the chief reason why 

 this method has not been extensively employed, as pointed out by Van 

 Slyke, is the technical difficulty of making the necessary analysis. 



It is most satisfactory to collect venous blood after a period (one hour 

 at least) of muscular rest (so that there is no excess of C0 2 ) and without 

 venous stasis, and to centrifuge without permitting any considerable loss 

 of carbonic acid. The latter precaution is necessary because there is a 

 migration of acid radicles, e. g., HC1, from plasma into corpuscles when 

 the C0 2 of the former is increased, and in the reverse direction when the 

 C0 2 is decreased. If the C0 2 in the blood were not the same during cen- 

 trifuging 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 



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. 



an atmosphere containing the same partial pressure of C0 2 as exists in 

 the body (i. e., the alveolar air) (see page 344), this has been found im- 

 practicable for general use, and is unnecessary if loss of C0 2 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 immediately delivered into a centrifuge 

 tube under paraffin oil, which by floating on its surface serves to diminish 

 free diffusion of C0 2 to the outside air (even though such oils dissolve 

 more C0 2 than water). To mix the blood with the oxalate, the syringe 

 should be moved backward and forward several times, but it must not b* 1 

 shaken. 



After centrifuging, about 3 c.c. of plasma are removed and saturated 

 with C0 ? at the same tension as in alveolar air (i. e., 5.5 per cent). 



