OPSONINS AND PHAGOCYTOSIS 167 



and believes that they perform somewhat different functions in the 

 body. 



Wright and Douglas, in 1902, published observations that 

 threw much needed light on the theory of phagocytosis. They 

 showed that, in most cases, at least, the bacteria would not be 

 destroyed by the white blood-cells or phagocytes in the absence 

 of blood-serum. They showed that the serum contained something 

 that rendered the bacteria positively chemotactic or attractive 

 for the phagocytes, and they accordingly named this something 

 opsonin (Gr. opsonein, to prepare a meal). 



Opsonins. Opsonins may be shown to be present in certain 

 sera by the following experiment: Blood of a suitable animal is 

 drawn into citrate solution and centrifuged, thus throwing the 



H, Si 



Fig. 78. Phagocytosis by human leukocytes: 1, Micrococcus aureus; 2, 

 Bacillus dysenteries; 3, B. typhosus; 4, B. tuberculosis; 5, Micrococcus meningi- 

 tidis (1, 2, and 3 adapted from Levaditi and Inman, 4 from Freeman, and 

 5 from Councilman). 



cellular elements to the bottom. The top layer of corpuscles, 

 or " cream/' containing a large proportion of leukocytes, is pipetted 

 off, and mixed with physiological salt solution and again centflfuged. 

 A second washing and centrifugation removes all traces of adher- 

 ent serum. The corpuscles are then mixed with a suspension of 

 the bacteria and incubated for fifteen minutes. At the end of 

 that period mounts are prepared, stained with a suitable blood- 

 stain, such as Jenner's or Wright's, and examined. The bacteria 

 will not, in general, be engulfed by the phagocytes. A similar 

 series carried through, but with the addition of a little immune 

 serum, would exhibit marked phagocytosis, and considerable 

 numbers of the microorganisms would be found within the leuko- 



