OPSONIC ACTION 181 



These results, as regards the specificity of the normal 

 opsonins, appear to be at variance with the results obtained 

 by Bulloch and Western. They found only a slight reduc- 

 tion of the tubercle opsonin of normal human serum on 

 treatment with the Staphylococcus aureus, and of the staphy- 

 lococcus opsonin on treatment with the tubercle bacillus. 

 As stated above, we found a great reduction of the staphy- 

 lococcus opsonin on treating the normal rabbit's serum 

 with the tubercle bacillus". The difference in the results prob- 

 ably depends upon the amount of the bacterial emulsion 

 employed. In every case we used a large amount ; in the 

 tubes after centrifugalization the volume of the deposit of 

 bacteria would be about a tenth of the volume of the serum, 

 sometimes more. This is, no doubt, a large quantity, 

 but it is to be noted that the same amounts were employed 

 in the case of the immune serum, and no diminution of the 

 opsonin was observed. The difference in the two kinds of 

 serum is, therefore, very remarkable. 



We have stated above that the opsonin for a particular 

 organism appears to be more rapidly removed from a normal 

 serum by an emulsion of that organism than of any other, 

 whilst at the same time any bacterial emulsion will absorb 

 large quantities of that opsonin. At present we are unable 

 to give the explanation of that fact. We use the term 

 ' normal opsonin ' for the labile substance which is destroyed 

 by heat, but we do not know whether or not another sub- 

 stance is present in small amount which acts as an immune- 

 body. The problem is very much the same as in the case of 

 bactericidal action. A closely analogous phenomenon was 

 demonstrated by Bordet 1 in the case of haemolysis. Normal 

 guinea-pig's serum, after treatment with rabbit's corpuscles, 

 is deprived of its lytic action for these corpuscles ; it still, 

 however, produces lysis of pigeon's corpuscles. If, how- 

 ever, the serum be treated by a more powerful absorber of 

 1 Bordet, Annales de Vlnst. Pasteur, 1901, p. 317. 



