CHAPTER XII 

 OPSONIC INDEX 



WHETHER opsonins are regarded as separate antibodies or as being 

 identical with complements and amboceptors, a measure of their quan- 

 tity and power may be of aid in formulating a diagnosis, as a guide to 

 active immunization, and as one means of determining the potency of 

 various immune serums used for therapeutic purposes, such as antimen- 

 ingococcus and antipneumococcus serums. We are mainly indebted 

 to Leishman, Wright and Douglas, Neufeld and Rimpau, and their 

 coworkers for devising a technic that, however imperfect it may be ac- 

 cording to the results obtained, has opened a new and important field 

 for the study of immunologic processes. 



Principle. This is based upon the method devised by Wright and 

 Douglas, whereby it was sought to determine the amount and kind of 

 opsonin in a patient's serum by comparing the degree of phagocytosis 

 with that occurring when normal serum was used. 



Definition. The opsonic index is the ratio of the number of bacteria 

 ingested by a given number of phagocytes in the presence of a patient's serum f 

 to the number ingested by the same number of phagocytes in the presence of 

 normal serum. 



"An equal volume of the patient's serum, measured in a capillary 

 pipet, is mixed with an equal volume of a suspension of washed leuko- 

 cytes derived from a normal blood. After this 'phagocytic mixture' 

 has been digested for a suitable period at 37 C., film preparations are 

 made and stained. 



"A 'phagocytic count' is then undertaken, i. e. } the average bacterial 

 ingest of the leukocytes in the phagocytic mixture is determined, and 

 this is compared with the average ingest of the leukocytes in a phago- 

 cytic mixture made with normal blood. 



"The expression thus obtained, 



Average ingest of the individual phagocyte in the mixture containing the 



patient's serum. 



Average ingest of the individual phagocyte in the mixture containing nor- 

 mal serum is denoted the opsonic index" (Wright). 



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