280 PHAGOCYTOSIS— OPSONINS 



proposed for these bodies the name opsonin, derived from a 

 Greek word signifying "to prepare a meal for." Neufeld 

 and Rimpau at about the same time (1904), in studying 

 immune sera, observed substances of similar action in these 

 sera and proposed the name bacteriotropijis, or bacteriotropic 

 substances. There is scarcely a doubt that the two names 

 are apphed to identical substances and that Wright's name 

 opsonin should have preference. 



The chemical nature of opsonins is not certainly deter- 

 mined, but they appear to be a distinct class of antibodies 

 and to possess two groups, a combining or haptophore and 

 a preparing or opsonic group, and hence are similar to anti- 

 bodies of Ehrlich's second order— agglutinins and precipi- 

 tins. Wright also showed that opsonins are just as specific 

 as agglutinins are— that is, a staphylococcus opsonin prepares 

 staphylococci only for phagocytosis and not streptococci or 

 any other bacteria. 



Wright showed that opsonins for many bacteria are 

 present in normal serum and that in the serum of an 

 animal which has been immunized against such bacteria the 

 opsonins are increased in amount. Also that in a person 

 infected with certain bacteria the opsonins are either 

 increased or diminished, depending on whether the progress 

 of the infection is favorable or unfavorable. The opsonic 

 power of a serum normal or otherwise is determined by mix- 

 ing a suspension of fresh leukocytes in normal saline solution 

 with a suspension of the bacteria and with the serum to be 

 tested. The leukocytes must first be washed in several 

 changes of normal salt solution to free them from any 

 adherent plasma or serum. The mixture is incubated for 

 about fifteen minutes and then slides are made, stained with 

 a good differential blood stain, Wright's or other, and the 

 average number of bacteria taken up by at least fifty phago- 

 cytes taken in order in a field is determined by counting 

 under the microscope. The number so obtained Wright 

 calls the phagocytic index of the serum tested. The phago- 

 cytic index of a given serum divided by the phagocytic 

 index of a normal serum gives the opsonic index of the serum 

 tested. Assuming the normal opsonic index to be 1, Wright 



