1 64 IMMUNE SERA 



some time later the bacteriolytic substances were 

 discovered. In both cases it was soon found that 

 these were but accompaniments of greater or less 

 significance to the complex phenomenon of immun- 

 ity. When we consider how manifold are the defen- 

 sive agencies which the animal organism possesses, 

 and how very complex they become the more they 

 are. studied, we shall not marvel at the absence of 

 parallelism between the clinical course of the disease 

 and the opsonic index. There is little doubt that 

 the opsonic indices do measure a certain fraction or 

 phase of the immunity reaction; we do not believe 

 that they replace clinical observations in measuring 

 the effect of immunizing injections. 



