192 Prof. Muir and Mr. Martin. On the Combining [Jan. 18, 



Normal Serum. 



Opsonic index. 



Normal serum of rabbit (unheated) 170 



„ „ treated once with staplrylococcus 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 



„ „ v 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 ther- 

 molabile opsonin has been destroyed by heat, the stable opsonin remains 

 practically unaffected by treatment which removes normal complement and 

 normal opsonin. In other words, substances which we may call complement- 

 absorbers do not fix or combine with the thermostable opsonin of the immune 

 serum. 



II. On the Eelative 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 hemolytic tests; it also 

 absorbs the opsonin of a normal serum as tested by the Staphylococcus aureus. 

 We have accordingly tested the effect on the opsonin of our immune serum. 

 In the following tables the comparative results are shown : — 



Normal Serum. 



Opsonic index. 



Normal serum of rabbit (unheated) 38'0 



., „ treated with Staphylococcus aureus 0'02 



„ „ „ Bacillus coli 3*3 



„ „ „ V. Metchnikovi 411 



„ „ „ Tuberculosis Bacillus 2'6 



„ „ „ Bacillus pyocyaneus 3*4 



