OPSONIC INDEX 157 



poured into a bottle or sealed off in a test-tube and shaken thoroughly in a shaker or 

 by hand. The emulsion is then centrifuged to throw down the bacterial clumps and 

 the supernatant slightly turbid bacterial suspension poured off. If working with a 

 dangerous pathogen it is advisable to kill the organisms as in making vaccines. 



Now with a capillary bulb pipette so graduated that the one volume mark con- 

 tains about two drops we draw up one volume of citrated salt solution. Then 

 having made a break with an air column, we take up one volume of the patient's 

 blood. Again make an air break and draw up one volume of the citrated salt solu- 

 tion bacterial emulsion. The three volumes are then immediately forced out into 

 a small test-tube, made from three inches of 3/16- inch glass tubing, as shown in the 

 Emery technic for the Wassermann. The citrate prevents coagulation of the blood 

 and the contents of the tube are well mixed by drawing up and ejecting with the 

 capillary bulb pipette. Incubate this small test-tube at body temperature for 

 15 minutes, shaking the contents once or twice during the incubation period. Ex- 

 actly at the expiration of the period of incubation (usually 15 minutes although at 

 times 10 minutes or 30 minutes may be desirable) place the tube in a centrifuge and 

 throw down the cell sediment. Next pipette off the supernatant fluid and then 

 plunge the pipette to the bottom of the tube and draw off the greater part of the 

 sediment at the bottom. This consists largely of the red cells the leukocyte layer 

 on the surface being undisturbed. 



Now mix the remaining cell sediment and smear out on a slide or preferably 

 between two cover-glasses as in Ehrlich's method. The smear is fixed by burning 

 off a film of alcohol and stained with dilute carbol fuchsin or methylene blue. The 

 granule staining with Wright's stain makes it slightly confusing. 



A second similar preparation but using blood from a normal person as a control 

 is then made. Counting the phagocytized bacteria in a given number of poly- 

 morphonuclears, we obtain an average number of bacteria phagocytized per cell. 

 Repeating the count with the control or normal blood, we likewise have the average 

 number of bacteria taken up per cell. Dividing the patient's average by the normal 

 average, we have the opsonic index. If the average for fifty of the patient's cells was 

 eight and that of the control only four, the patient's index would be two, or twice the 

 normal. The practical value of this test is that where two or more organisms are in a 

 body fluid we may ascertain the causative organism by noting marked variation 

 from the normal in the patient's opsonic index for that particular organism and not 

 for the other organism. This variation may be of the nature of a high or low opsonic 

 index. 



METHOD or WRIGHT FOR OBTAINING OPSONIC INDEX. 



While other observers had previously noted the presence of sub- 

 stances in immune sera which so acted on the bacteria that phagocytosis 

 was made possible, yet it was to Wright and Douglas, in 1903, that the 

 existence of this factor in phagocytosis was brought forward and the 

 estimation of such substances made practicable. 



To this substance the name opsonin was given 'the Greek word 



