THE OPSONIC INDEX 229 



and should not be confounded with bacteriolysins, 

 another type of antibody. Moreover, it has been 

 shown that opsonins are divisible into thermolabile 

 (the normal opsonin of Wright) and thermostable 

 ( immune opsonin ) . The former are readily destroyed 

 at a temperature of dQ"" C, the latter retain their bac- 

 teriotropic property in spite of this degree of heat. 



By virtue of the assiduous labors of Wright and 

 his co-workers in evolving a technic (determination of 

 the opsonic index) to measure phagocytosis (degree 

 of immunization), therapy by bacterial inoculations 

 was revived and popularized to an unprecedented ex- 

 tent and has led to the application of active immuniza- 

 tion of far-reaching consequences, and it is for this 

 reason that medicine owes Wright a perennial debt. 



The opsonic index may he described as the measure 

 of the ratio of the phagocytic activity of neutral or 

 washed leucocytes in the patient's serum for given 

 bacteria, as compared with those in a normal or con- 

 trol serum. Inasmuch as a neutral phagocyte will in- 

 gest the same number of bacteria, provided the two 

 sera possess identical qualities, the normal or base line 

 is arbitrarily taken as one. If, in the ease of the pa- 

 tient's serum, it is found that 100 leucocytes contain 

 900 bacteria, while the same number of leucocytes 

 treated with the control serum contain 1000 bacteria, 



