320 GENERAL MICROBIOLOGY 



small test tube and either allowed to clot and the serum 

 removed, or it is defibrinated and centrifuged. In either 

 case the serum should be used within three to four hours 

 from the time the blood is drawn. 



5. Make the test as follows : 



a. With a diamond point or wax pencil make a mark on 

 the drawn out arm of the mixing pipette about 2 cm. from 

 the end. 



b. With the aid of a rubber bulb on the opposite end, 

 draw a column of the bacterial suspension up to the mark, 

 admit a bubble of air, then draw a column of leucocytes 

 up to the mark and another bubble of air, then a column 

 of the serum to be tested. 



c. Mix these by forcing out on a glass slide or into a 

 small test tube and drawing up again, repeating once or 

 twice, being careful to avoid introducing air bubbles. 



d. Finally draw up the mixture into the pipette and seal 

 the end of pipette in the flame, using care not to heat the 

 mixture. 



e. Incubate fifteen minutes with frequent shaking. 



/. Then place a drop on a slide and make a thin film 

 made as in the preparation of a blood film, dry and stain 

 with Wright's or Jenner's stain. 



6. Repeat the experiment, using the normal serum. 



7. With an oil immersion lens count the number of 

 organisms taken up by fifty leucocytes on each slide and 

 calculate the average number taken up by each. The 

 result is the opsonic power of the serum. 



8. The opsonic index is the ratio of the opsonic power 

 of the suspected serum to that of the normal serum. 



Example. If the average number of bacteria taken up 

 by the leucocytes in the presence of the suspect serum is 

 5.6 and the average number taken up by the leucocytes in 

 the presence of the normal serum is 4.8, the opsonic index 

 of the suspect serum is determined as follows: 5.6^-4.8 = 

 1.16+ opsonic index. 



