178 ANTI-BACTERIAL PROPERTIES OF SERUM 



an example in which the effects on the normal and the 

 immune serum of the rabbit are once more compared : 



Normal Serum 



Opsonic count 



Normal serum of rabbit (unheated) 17-0 



treated once with staphylococcus emulsion 1-6 



twice 0-25 



once with serum precipitate . . 11-3 



twice 0-3 



Immune Serum 



Anti-staphylococcus serum (heated at 55 C.) . . . . 23-3 



treated once with staphylococcus emulsion 23-0 



twice 2-2 



once with precipitate . . 25-0 



twice ... 23-0 



The result, again, is that the serum precipitate removes 

 the opsonin from the normal serum, but has no effect on the 

 stable opsonin of the immune serum. 



Summary. It appears, from the above experiments, that 

 in the case of a fresh anti-staphylococcus serum the effect 

 of treating with substances which absorb complement is 

 practically the same as heating the serum, there being a 

 considerable residuum of opsonin in both cases. Further, 

 after the thermolabile opsonin has been destroyed by heat, 

 the stable opsonin remains practically unaffected by treat- 

 ment which removes normal complement and normal 

 opsonin. In other words, substances which we may call 

 complement-absorbers do not fix or combine with the thermo- 

 stable opsonin of the immune serum. 



II. ON THE RELATIVE SPECIFICITY OF NORMAL AND 

 IMMUNE OPSONINS 



An emulsion of dead bacteria is well known to have the 

 power of absorbing serum complements, as shown, for 

 example, by hsemolytic tests ; it also absorbs the opsonin of 



