172 ANTI-BACTERIAL PROPERTIES OF SERUM 



(6) ON THE COMBINING PROPERTIES OF THE 

 OPSONIN OF AN IMMUNE SERUM 



In the previous section we have studied the combining 

 properties of the thermolabile opsonins of normal sera, and 

 have shown that various substances or combinations of 

 substances which absorb serum complements also absorb 

 the opsonins in question. Of special interest is the fact 

 that red corpuscles, and also heated normal sera, which by 

 themselves have no appreciable effect either on complements 

 or on opsonins, absorb or fix both of these bodies when 

 combined with their corresponding anti-substances, immune- 

 bodies and precipitins respectively. Since these results were 

 published we have extended our experiments, and have 

 always obtained the same result the opsonin is always 

 fixed when the complement is fixed. Using the term 

 complement in the bio-chemical sense, we have said 

 that the normal thermolabile opsonins belong to the group 

 of complements. And we have also found that just as 

 complements in their combining affinities do not possess 

 specific properties, but are absorbed by a great many 

 different substances, so also these thermolabile opsonins 

 show a corresponding community in their combining relation- 

 ships. We, however, expressly left out of consideration (a) the 

 special opsonins of immune sera, and also (6) the thermo- 

 stable opsonins of normal sera, of which latter the stable 

 opsonin of human serum for the diphtheria bacillus may be 

 taken as an example. In the present communication we 

 shall consider the thermostable opsonins of immune sera. 



It is unnecessary to enter in detail into the literature of 



the subject, as this has been already done by Dean. 1 It is, 



however, advisable for the sake of clearness to refer to the 



chief facts which have been established and to the chief 



1 Dean, Roy. Soc. Proc., vol. Ixxvi, p. 515. 



