1907.] Properties of the Opsonin of an Immune Serum, 191 



In this case there was an enormous excess of precipitate, the actual bulk 

 of the precipitate being three times that of the serum ; there would, therefore, 

 probably be some dilution of the serum. The treated serum has practically 

 the same opsonic value as the heated. 



Treatment by Precipitate* 



Opsonic index. 

 Anti-staphylococcus serum — 



Heated at 55° C 7*2 



Heated and treated with precipitate 7 *0 



Normal serum — 



Unheated 24*6 



Unheated and treated 0*86 



Treatment by Bed Corpuscles + Immune-Body. 



Anti-staphylococcus serum — 



Heated at 55° C 8*3 



Heated and treated 9'4 



Normal serum — 



Unheated 20'8 



Unheated and treated < 0*8 



The opsonin of the normal serum is absorbed, whereas that of the immune 

 serum is unaffected. 



Treatment by Emulsion of V. Metchnikovi + Immune-Body. 



Opsonic index. 



Anti-staphylococcus serum — 



Heated at 55° C. 17'2 



Heated and treated 17*5 



Normal serum — 



Unheated 25*0 



Unheated and treated 2'36 



The result is the same as before. 



We have also endeavoured to remove the opsonin of the immune serum by 

 treating it twice with a considerable quantity of serum precipitate, the pre- 

 cipitate being separated by centrifugalisation after each treatment, but no 

 diminution of the opsonin has resulted. The following is an example in 

 which the effects on the normal and the immune serum of the rabbit are 

 once more compared : — 



* In this and the two following experiments the anti-serum was the one which we 

 obtai ned from Dr. Dean. 



