OPSONIC ACTION 183 



opsonic power gave the following results: emulsion of 

 staphylococci alone took up 0-03 c.c. of guinea-pig's com- 

 plement, 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. 1 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 containing no 

 immune-body, but this we have not yet obtained. 



Note. It is to be noted that in speaking of the 

 opsonin of an immune serum we mean the thermostable 

 anti-substance which by itself has an opsonic effect ; the 

 question is as to whether or not this is simply an immune- 

 body. That an immune-body may increase the opsonic 

 effect of an unheated immune serum, by leading to the 

 absorption of more complement opsonin, follows from what 

 has been stated above (p. 167). But this is, of course, 

 another matter (vide p. 188). 



If the opsonin has the constitution of an agglutinin, that 

 is, possesses merely a combining and an active (agglutinating) 

 group, is the opsonin merely the agglutinin ? To this 

 question we can give no definite answer. We have tested 



1 In a third anti-staphylococcus serum which we have recently examined, 

 a considerable amount of immune-body, as shown by absorption of com- 

 plement, was present, yet its opsonic effect was not superior to that of the 

 other two sera. 



