30 METHODS OF OBTAINING HUMAN AND ANIMAL BLOOD 



rubber tubing with a capillary pipet, which permits the supernatant 

 fluid flush with the sediment to be removed. 



3. After the last washing the supernatant salt solution should be 

 carefully removed, when the corpuscles are ready for use. 



OBTAINING BLOOD-SERUM 



If serum is desired at once, blood should be drawn into sterile cen- 

 trifuge tubes and the tube immersed in cold water for from five to ten 

 minutes; this facilitates clotting. The clot is then broken up with a 

 sterile platinum wire or glass rod, and the serum secured by rapid 

 centrifugalization. Or blood may be drawn into sterile cylinders, 

 Petri dishes, or centrifuge tubes, and allowed to stand at room temper- 

 ature for a few hours, after which they should be placed in a refrigerator 

 until the serum separates. Blood never should be drawn into Erlen- 

 meyer flasks because of the difficulty of drawing off serum without dis- 

 turbing the clot. When drawn into Petri dishes, care should be taken 

 that the layer of blood is not too thin, otherwise drying will occur with 

 poor separation of the serum. As a rule, the best results are secured 

 by placing blood in centrifuge tubes, for if separation is poor or does not 

 occur at all, the clot may be broken up and serum secured by centrif- 

 ugalization. So far as possible, avoid drawing blood from an animal 

 immediately after feeding, as under these circumstances the serum is 

 likely to be milky or opalescent. 



OBTAINING CORPUSCLES AND SERUM 



For certain purposes it may be desirable to obtain both serum and 

 corpuscles; these may be secured in the following way: 



1. Place blood in a large centrifuge tube or cylinder, and defibrinate 

 with rods or glass beads. 



2. Centrifuge thoroughly. 



3. Remove the serum, which is slightly discolored on account of 

 defibrination, with capillary tube and rubber teat. 



4. Filter the corpuscles into a centrifuge tube through a wisp of 

 cotton in a funnel to remove small particles of fibrin. 



5. Add normal salt solution, and proceed with the washing process. 



OBTAINING BLOOD PLASMA 



In obtaining blood plasma it is necessary to avoid coagulation of 

 blood by securing and handling the blood with the least amount of 



