1907.] Properties of the Opsonin of an Immune Serum. 195 



opsonin than the emulsion untreated, the amount of opsonin left being 

 practically the same as when the serum is heated. The following is an 

 additional example : — 



Opsonic Action of Normal Human Serum on the Tubercle Bacillus. 



Opsonic index. 



Normal serum unheated 6*5 



„ „ heated at 55° C 0"2 



treated with emulsion of V. Metchnihovi 



+ immune-body 0'19 



» 5J 



III. The Kelations of the Opsonin of an Immune Serum. 



Our results, as above detailed, show that the opsonin of the anti-staphylo- 

 coccus serum corresponds as regards specificity and combining relationships 

 with true anti-substances developed in the process of immunisation. Does it 

 correspond with the type of an immune-body or of an agglutinin ? Does it 

 in combination with its corresponding receptor lead to the absorption of 

 complement, or does it not ? In the first place, it is certain that every 

 immune-body does not produce an opsonic effect. We have an anti-coli 

 serum, for example, which contains immune-body in considerable quantity, 

 but it has no opsonic effect. A given amount of emulsion of the B. coli alone 

 was found to take up 0*04 c.c. of guinea-pig's complement, while the same 

 amount of emulsion treated with the anti-serum took up 0*12 c.c, the 

 absorption of complement being tested by the usual hemolytic methods. In 

 the case of the anti-staphylococcic serum the amount of immune-body 

 appeared to be considerably less. The sample with the greatest opsonic 

 power gave the following results : — emulsion of staphylococci alone took up 

 0*03 c.c. of guinea-pig's complement, the same quantity treated with immune- 

 body took up 0*075 c.c. This sample had a very powerful opsonic action, 

 giving, when heated, an average count of 20 cocci per leucocyte in the usual 

 test. The anti-staphylococcus serum which we got from Dr. Dean had a 

 weaker though still very decided opsonic action, yet it produced a scarcely 

 perceptible increase in the amount of complement absorbed ; that is, it 

 contained a mere trace of immune-body. We are inclined to think from 

 these results that the opsonin in an immune serum may not be an immune- 

 body, but has the constitution of an agglutinin. But this is merely an 

 expression of opinion, as we know nothing with regard to the real amounts of 

 these substances. In order to say that the immune-body did not act as 

 opsonin, we would need to get an anti-serum with opsonic effect but contain- 

 ing no immune-body, and this we have not yet obtained. 



If the opsonin has the constitution of an agglutinin, that is, possesses 

 merely a combining and an active (agglutinating) group, is the opsonin 



