OBTAINING BLOOD PLASMA 



31 



trauma to leukocytes (paraffined tubes), and centrifuging rapidly and 

 at once in cold centrifuge tubes. 



1. After warming a centrifuge tube immerse in hot molten paraffin. 

 Remove, drain, and allow the paraffin to harden. This produces a 

 thin coat of paraffin within the tube; if a thicker one is desired, im- 

 merse again until a coat of the desired thickness is obtained; chill the 

 tube thoroughly in cracked ice, but avoid getting water inside the 

 tube. 



2. Blood should be secured quickly by venipuncture, using a dry 

 sterile needle, and passing the blood into a paraffined tube. 



FIG. 10. METHOD OF PRICKING A FINGER. 



The patient's finger is grasped firmly and lanced with a Daland lancet across 

 the folds of skin. When lanced parallel with the skin-folds, the wound is likely to 

 close before sufficient blood is secured. 



3. Centrifuge at once and at high speed. If this is not possible, 

 pack the tube in a large centrifuge cup, and surround with finely cracked 

 ice. This permits of more prolonged centrifugalization, and at lower 

 speed, and yields a hemoglobin-free plasma. 



4. The clear yellow plasma is removed at once with pipet and nipple. 



