PHAGOCYTOSIS— OPSONINS 257 



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 baderiotropins, or bacteriotropic 

 substances. There is scarcely a doubt that the two names 

 are applied 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 micrococcus opsonin prepares 

 micrococci 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 infec- 

 tion is favorable or unfavorable. The opsonic power of a 

 serum normal or otherwise is determined by mixing an 

 emulsion of fresh leukocytes in normal saline solution with 

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

 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 min- 

 utes and then slides are made, stained with a good differ- 

 ential blood stain, Wright's or other, and the average num- 

 ber of bacteria taken up by at least fifty phagocytes 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 phagocytic index 

 of a given serum divided by the phagocytic index of a nor- 

 mal serum gives the opsonic index of the serum tested. 

 Assuming the normal opsonic index to be 1, Wright asserts 

 that in healthy individuals the range should be not more 

 17 



