I 



4 LABORATORY COURSE IN SERUM STUDY 



plug being thrown to the bottom of the tube during centrifuga- 

 tion. The cotton plug may also be replaced by a cap of sterile 

 tin foil. After careful balancing, the tubes are centrifugalized 

 at high speed until the sediment is thrown down. The super- 

 natant fluid is removed with a sterile pipette and in this case 

 should be preserved for the injection of rabbits for the production 

 of precipitins. The tubes are then filled with sterile salt solution, 

 the blood cells resuspended by drawing them in and out of a 

 pipette and again thrown down in the centrifuge. This process 

 is repeated three times. The washed sediment is then trans- 

 ferred to another tube with a graduated pipette and an equal 

 amount of salt solution added to make the 50 % suspension which 

 is used for injection. 



2. PREPARATION OF BACTERIAL EMULSIONS 



Ten c.c. of sterile salt solution are added by means of a pipette 

 to a 24-hour culture on slant agar of the particular organism to 

 be used. Surface growth is scraped from the agar by means of 

 a platinum loop and the bacteria suspended in salt solution by 

 gentle shaking. The suspension is then poured off into a sterile 

 test tube, carefully flaming the mouths both of the culture tube 

 and the sterile test tube before pouring. The second tube may 

 then be drawn out and sealed in a blowpipe flame, and the tube 

 entirely immersed in a water bath for sterilization ; or the upper 

 portion of the tube may be carefully heated in a Bunsen flame to 

 kill any bacteria which may be adherent to the side of the upper 

 portion, and when the tube has cooled the lower portion is then 

 immersed in a water bath, taking care that the level of the water 

 comes well above the portion which has not been sterilized by 

 flaming. The bacteria should be heated at 60 C. for one half 

 hour and are then ready for injection. 



3. PREPARATION OF SERUM FOR INJECTION 



The serum or ascitic fluid used for the production of precipitins 

 should be clear and sterile and is less toxic if heated for 30 minutes 

 at 56 C. before injection. It requires no other preparation. 



