180 ANTI-BACTERIAL PROPERTIES OF SERUM 



out a very marked difference as regards specificity between 

 the opsonins of a normal and of an immune serum. With 

 the exception of the possible slight effect in the case of the 

 Staphylococcus albus, we have failed to find any organism, 

 except the Staphylococcus aureus, which absorbs the opsonin 

 from the heated anti-staphylococcus serum. In the case of 

 the opsonins of a normal unheated serum, the result is 

 entirely different, as is shown by the table given above. 

 Every organism tested has absorbed large quantities of 

 opsonin when the Staphylococcus aureus is used as the test 

 for opsonic action. 1 At the same time, the Staphylococcus 

 appears to remove this opsonin more quickly than any of 

 the others. We have tested to what extent it is possible 

 to remove the opsonin of normal serum for Staphylococcus 

 aureus by treating the serum twice with an emulsion of 

 another organism, e. g. the B. coli. The results are : 



Normal Serum 



Opsonic count 



Guinea-pig's serum (unheated) 21-5 



treated once with Staphylococcus aureus 1-0 



twice 04 



once with B. coli . . .2-1 



twice ... 1-3 



There is, therefore, only a slight difference as regards 

 absorbing powers in favour of the Staphylococcus aureus. 



The immune serum was tested at the same time, and 

 once more a great difference was brought out. 



Immune Serum 



Opsonic count 



Anti-staphylococcus serum (heated at 55 C.) . . 26-7 



treated twice with B. coli . . 25-4 



Staphylococcus aureus 1-6 



1 These results, so far as the normal opsonins are concerned, are in 

 harmony with those of Simon, Lamar, and Bispham, whose paper (Journ. 

 of Exper. Med., December, 1906, p. 651) came into our hands after our 

 original communication was written. 



