1907.] Properties of the Opsonin of an Immune Serum, 189 



certain cases the serum of patients suffering from tuberculosis may contain 

 a considerable proportion of 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 thermostable is 

 increased. He, however, mentions the possibility that the opsonic effect 

 of a normal serum may in part be due to complement. Wright and Eeid 

 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 complements. 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* to a certain 

 extent, and also by Hektoenf 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 serum, giving in each instance for 

 comparison the effects on normal opsonins under the same conditions of 

 experiment. We have made use of two samples of an ti-staphylococcic serum. 

 One of these was kindly given to us by Dr. Dean, for which we have 

 pleasure in recording our indebtedness, whilst the other was obtained by 

 us from a rabbit by repeated intravenous injections of dead cultures of 

 Staphylococcus aureus. As it was employed at various stages in the process 

 of immunisation, the degree of the opsonic effect varies considerably in the 

 different experiments. We may state that heating for several hours at 

 55° C. appears to have no appreciable effect on the thermostable immune 

 opsonin. The serum thus contrasts very markedly with the normal rabbit's 

 serum, the opsonic effect of which is practically destroyed by heating for an 

 hour at 55° C. 



* Bulloch and Western, <Koy. Soc. Proc.,' vol. 77, 531. 

 t Hektoen ' Journ. of Infectious Diseases,' 1906, p. 721. 



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