260 



OPSONIC TECHNIQUE 



ground up in a mortar with saline solution before use. The 

 mixtures of leucocytes, bacteria, and serum are made in capillary 

 pipettes mounted with an indiarubber nipple, and furnished with 

 a unit mark about i inch from the free tip, which is drawn to 

 a fine point. The process is as follows : As much cream as will 

 reach to the unit mark is drawn into the pipette, then a little air 

 (to serve as an index), then a unit of the emulsion, another bubble 

 of air, and finally a unit of serum. These are then blown out on 

 to a glass surface, mixed intimately together, sucked into the 

 tube, the end of which is now sealed. The tube is now placed in 

 the incubator and the time accurately noted. Then the process 



FIG. 57. WRIGHT'S CAPILLARY PIPETTES, AS USED IN DETERMINATIONS 

 OF THE OPSONIC INDEX. (Emery's " Clinical Bacteriology and 

 Haematology.") 



The small figure shows the tip magnified. The middle figure shows the 

 pipette charged with leucocytic cream (in this case two volumes are 

 shown), emulsion of bacteria, and serum. In the lowermost figure these 

 are mixed together and the tip sealed. 



is repeated in exactly the same way, but the control serum is used 

 instead of that which is being investigated. Each pipette is 

 incubated for exactly the same length of time, removed from the 

 incubator, the tip broken off, the contents expelled, and films 

 made. These are obtained in a suitable way, examined under the 

 microscope, and the number of bacteria which have been taken 

 up by 50 or 100 poly nuclear leucocytes is counted in each. 

 Thus we may find that in the control specimen (in which 

 healthy blood was used) there are 300 bacteria in 100 leucocytes ; 

 in this case we say the " phagocytic index " is 3. In the other 

 specimen (in which the patient's blood was used) we might find 

 150 bacteria in 100 leucocytes, giving a phagocytic index of 1*5. 



