THE OPSONIC INDEX 241 



bacterium, or in the course of immunization to select 

 from time to time the bacterin to which the index is 

 low. It is generally admitted that the error due to 

 technic alone, aside from the question of personal 

 equation, amounts to one- to two-tenths. This varia- 

 bility is dependent particularly upon ( 1 ) the number 

 of cells counted and ( 2 ) the concentration of the bac- 

 terial suspension (Fig. 35). 



16 



