SERUM DIAGNOSIS 167 



Opsonins exist in the tissue fluids and are sub- 

 stances which are capable of rendering bacteria 

 more susceptible to phagocytosis. 



THE TECHNIC OF THE OPSONIC INDEX 



The reagents taking part in the opsonic reac- 

 tion are: (1) The serum to be tested; (2) Nor- 

 mal serum which is used as a control ; (3) Leuko- 

 cytic suspension, and (4) The bacterial suspen- 

 sion. 



Leukocytic Suspension If human leukocytes 

 are used, they may be obtained by puncturing 

 the lobe of the ear or the tip of the finger with 

 a lancet, and allowing the blood to flow into a 

 solution of one per cent sodium citrate and 0.85 

 per cent sodium chloride solution. The citrate 

 solution keeps the blood from clotting until the 

 corpuscles are separated from the citrate solu- 

 tion by centrifugalization. Animal leukocytes 

 may be obtained from the guinea-pig or rabbit 

 by injecting the animal with a solution of pep- 

 tone and collecting the peritoneal exudate eigh- 

 teen hours later. The leukocytes from whatever 

 source are washed three times with 0.85 per 

 cent salt solution by centrifugalization. After 

 the third centrifugalization, the supernatant 



