174 ANTI-BACTERIAL PROPERTIES OF SERUM 



heat-resisting opsonin, a circumstance which may aid the 

 diagnosis. The question therefore arises as to what is the 

 relationship between the thermolabile and the thermostable 

 opsonins. Dean thinks that the opsonin is of the nature 

 of an immune substance, and that in the case of normal 

 serum it undergoes a large fractional destruction by heat, 

 whereas in an immune serum the portion which is thermo- 

 stable is increased. He, however, mentions the possibility 

 that the opsonic effect of a normal serum may in part be due 

 to complement. 1 Wright and Reid consider that the opsonin 

 in a normal and in an immune serum alike is one and the 

 same, and prefer to call it thermolabile. The question as 

 to the identity of such substances may be studied in other 

 ways than that of testing their powers of resistance to heat. 

 One method is to test whether cell-receptors combined with 

 their corresponding immune-bodies will take up the opsonins 

 of immune sera, as we have shown that they take up the 

 labile opsonins of normal sera and as they take up comple- 

 ments. Another method is to test the degree of specificity 

 in their combining affinities to test, that is, to what extent 

 one bacterium will absorb the opsonins for other bacteria. 

 This has been done by Bulloch and Western 2 to a certain 

 extent, and also by Hektoen 3 in the case of hsemopsonins, 

 and to these experiments further reference will be made 

 below. But the method has not been carried out fully in a 

 comparative way as between normal and immune sera 

 respectively. 



We shall now give an account of experiments performed 

 by us to elucidate these questions in the case of an immune 



1 In his more recent publications he expresses definitely the opinion 

 that this is the case, and considers that the opsonic action of a normal 

 and immune serum alike resembles haemolytic action in being due to the 

 co-operation of immune-body (present in traces in normal serum) and of 

 complement. 



2 Bulloch and Western, Roy. Soc. Proc., vol. Ixxvii, p. 531. 



3 Hektoen, Journ. of Infectious Diseases, 1906, p. 721. 



