OPSONINS AND PHAGOCYTOSIS 171 



about 2 cm., from the end. The suspension of leukocytes is then 

 drawn up to the mark, then an air-bubble is admitted, then the 

 serum to be tested to the same mark, a second air-bubble, and 

 finally an equal amount of the bacterial suspension. The contents 

 of the tube are blown out upon a glass plate or into a watch-glass 

 and thoroughly mixed. This mixture is again drawn some dis- 

 tance into the capillary pipette and the end sealed in the flame. 

 It is then kept at 37 for fifteen minutes, preferably in an opsonic 

 incubator, where it may be rotated frequently to secure thorough 

 mixture. The end is then broken from the pipette, and smears 

 are made and stained with some good blood-stain, such as Wright's 

 or Jenner's modification of the Romanowsky, which will stain 

 bacteria. Special staining methods must sometimes be used, as in 

 the examination of the tubercle bacillus. 



Determination of the Opsonic Index. The total number of 

 bacteria ingested by 100 polymorphonuclear leukocytes is 

 counted. This number is determined both with normal serum 

 and the serum to be tested. The ratio between the number of 

 organisms ingested by the leukocytes, when treated with the 

 specific serum and when treated with normal serum, is called the 



opsonic index. Let y equal opsonic index where a is average 

 number of bacteria ingested per leukocyte when treated with a 

 specific serum; b is average number of bacteria ingested per leuko- 

 cyte with normal serum. In general, the opsonic index is found to 

 be low (less than unity) in chronic bacterial infections. 



McCampbeWs Modification of Opsonic Test. McCampbell has 

 considerably shortened the technic in veterinary practice as fol- 

 lows: The bacterial suspension containing 0.8 per cent, sodium 

 citrate is drawn to the 0.5 mark on the leukocyte pipette of a 

 hemocytometer, the specific blood to be tested is drawn to the 

 same mark, then all drawn into the bulb, mixed, replaced in the 

 capillary tube, and the whole wrapped with a rubber band and 

 incubated. The same procedure is carried through with normal 

 blood. The disadvantages of this method are the presence of 

 sodium citrate, which interferes to a slight degree with action of 

 opsonins, and the use of two lots of leukocytes from two animals, 

 one diseased and the other normal. Smears and examinations 



