OPSONINS, AGGLUTININS, PRECIPITINS, LYSINS 135 



normal salt solution. The suspension should only be moderately 

 thick and when thoroughly mixed should be centrifuged to remove 

 all clumps. 



By means of a capillary pipette marked about one inch from 

 the end, equal amounts of the three fluids, i.e. patient's serum, 

 leukocytes, and bacterial suspension, are drawn up into the tube, 

 an air space being left between each. All are then expelled upon 

 a slide and thoroughly mixed by being drawn into the tube and 

 again expelled several times. Finally the mixture is drawn into 

 the tube, the end is sealed, and the tube is placed in an incubator 

 at 37 C. Exactly the same procedure is repeated, using normal 

 serum in place of the patient's serum. After fifteen minutes' 

 incubation a large drop of the mixture from the tube containing 

 the patient's serum is smeared on a slide by means of a second 

 slide as for an ordinary blood film. A second slide is prepared in 

 the same manner from the tube containing the normal serum, 

 and both films are dried, fixed, and stained. The slides are then 

 examined. The number of bacteria are counted in fifty or one 

 hundred leukocytes and the average determined by dividing the 

 total number of bacteria counted by the number of leukocytes in 

 which they were found. This gives the phagocytic index. The 

 opsonic index is then determined by dividing the phagocytic index 

 of the patient by that of the healthy individual. Thus, if the 

 average number of bacilli influenced by the opsonin in the patient's 

 serum and taken up by the phagocytes is three, and the average 

 number taken up by the leukocytes after being acted upon by 

 normal blood is four, then the opsonic index will be f of one or 0.75. 

 For example : 



3= patient's phagocytic index _~ _. 

 4= normal phagocytic index 



Normally the opsonic index may vary between 0.8 and 1.2. A 

 higher index is regarded as indicative of increased resistance and 

 an index below normal as diagnostic of infection with the specific 

 organism tested. In the above case the patient's index is below 

 normal, consequently an infection might be assumed. 



