186 ANTI-BACTERIAL PROPERTIES OP SERUM 



of opsonic effect for a particular organism when treated with 

 an emulsion of that organism at C., as was shown by 

 Bulloch and Atkin, and this might be due to the absorption 

 of a natural immune-body at the low temperature. Dean in 

 his first paper also showed that, in the case of the staphy- 

 lococcus aureus, there remains in human serum after heating 

 at 55 C. a small quantity of thermostable substance which 

 has opsonic effect. On the other hand, there is evidence 

 that normal thermolabile opsonin unites directly with 

 bacteria. The fact that the normal opsonin for the one 

 organism can be removed by treatment with emulsions of 

 other organisms, provided a sufficient quantity be used, 

 shows this ; unless we are to assume that for all these 

 organisms there are present sufficient normal immune- 

 bodies to bring the whole of the complement into combina- 

 tion. For example, an emulsion of B. coli removes the 

 normal opsonin for staphylococcus aureus. If this depends 

 on a natural immune-body for bacillus coli the molecules of 

 this immune-body must at least be in a number to corre- 

 spond with the whole complement content of the serum, 

 and ascertained facts as to the manner in which comple- 

 ment-opsonin is taken up by untreated and by sensitized 

 bacteria respectively, are against such an assumption 

 (p. 167); in fact the only conclusion possible seems to be 

 that there is not sufficient natural immune-body in a 

 normal serum to correspond with the amount of comple- 

 ment opsonin, but if we add a sufficient amount of bacteria 

 the organisms can remove the complement opsonin by direct 

 combination. This question is discussed further in con- 

 nexion with bactericidal action (p. 203). If then the normal 

 complement opsonin combines directly with organisms we 

 must believe that it has opsonic action. It would be unjustifi- 

 able to suppose that it is without action unless it is brought 

 into combination through the medium of an immune-body. 

 This subject is also referred to in connexion with the 



