OPSONIC ACTION 185 



2. The thermostable opsonin of the anti-serum investi- 

 gated is a true anti-substance, and possesses the compara- 

 tively specific characters of anti-substances in general; it 

 is left undetermined whether it has the constitution of an 

 agglutinin or of an immune-body, though certain facts point 

 in favour of the former. 



3. Emulsions of other organisms than the organism used 

 in immunization (Staphylococcus aureus) do not absorb the 

 immune opsonin ; on the other hand, they absorb large 

 amounts of the normal complement-like opsonin. 



4. Powerful complement-absorbers red corpuscles or 

 bacteria treated with immune-body, or serum precipitate 

 have no effect on the thermostable immune opsonin, whereas 

 they remove almost completely the labile opsonin of the 

 normal and the immune serum alike. 



ADDENDUM 



Although the more important practical points appear to 

 us to have been brought out by the investigations above 

 detailed, some theoretical questions with regard to opsonic 

 action may be referred to. Attempts have been made to 

 explain all the opsonic phenomena as conforming with the 

 scheme of haemolysis, according to which haemolysis by a 

 natural serum depends upon a natural immune-body in 

 association with complement, and haemolysis by an immune 

 serum depends upon an artificially developed immune-body 

 in association with complement, the immune-body itself 

 having no effect. In a corresponding manner the opsonic 

 action by a normal serum would be due to a natural immune- 

 body acting along with complement opsonin, and the 

 opsonic action of an immune serum would be due to an 

 artificially developed immune : body also acting in association 

 with complement. Now there are a certain number of facts 

 which support such a view. There is, in the first place, the 

 fact that the normal serum may lose a considerable amount 



