CHAPTER III. 



THE OPSONIC INDEX 



From the foregoing chapter it is seen that since the work 

 of Denys and LeClef in 1895, it has been known that serum is of 

 importance in phagocytosis. Little attention, however, was 

 given to the various observations on this subject until the work 

 of Wright and Douglas was presented. Although Neufeld and 

 Rimpau discovered probably the same substances as Wright and 

 Douglas, these investigators are seldom referred to in the discusion 

 of the substances that change bacteria so as to prepare them tor 

 ingestion by leucocytes. There are two definite scientific reasons 

 for the great prominence given to the work of Wright and Doug- 

 las: one is that they advanced and improved a technique for the 

 determination of the amount of phagocytosis, by means of which 

 the opsonic index could be determined; the other is to be found 

 in the widespread interest in the methods they advanced for 

 active immunization of patients by the injection of killed cultures. 



In 1902 Leishman presented a method for the quantitative 

 determination of phagocytosis. He mixed equal quantities of 

 patient's blood and bacterial emulsion, which he then incubated 

 for a time in a moist chamber. After incubation he made cover 

 glass spreads which he dried, fixed and stained. On these slides 

 he counted the number of bacteria ingested by the leucocytes, 

 from which the average number per leucocyte was determined. 

 This average he compared with the average per leucocyte obtained 

 when normal blood instead of patient's was added to the bacterial 

 emulsion. Leishman did not take into consideration the action 

 of serum on bacteria or leucocytes but devised merely a "method 

 of estimating phagocytic power." 



Wright and Douglas, in their work on the determination of 

 the opsonic index modified Leishman's method to meet their 

 theory on phagocytosis. According to their observation opsonin 



