36 VACCINE AND SERUM THERAPY. 



a certain leucocytic cream and bacterial suspension, by the pha- 

 gocytic index obtained when serum from the healthy individual 

 is used with the same leucocytic cream and bacterial emulsion. 

 This may be illustrated in a concrete case as follows : If the aver- 

 age number of staphylococci phagpcytosed as determined by 

 counting the cocci in fifty leucocytes is eight when the patient 

 serum is used, and ten when normal serum is used, then eight- 

 tenths or 0.8 is the opsonic index. 



