Modern Theories of Bacterial 

 Immunity. 



I. 



Immunity in the bacterial infectious processes 

 is divided into: 



Natural Immunity. — By this term is meant 

 the ability to resist the invasion of infectious 

 agencies, which is often found under natural 

 conditions, e.g., the resistance of many races of 

 animals to infection with typhoid fever, or the 

 resistance of the human race to hog cholera; 

 and 



Acquired Immunity. — This form of immu- 

 nity is said to occur when the condition of re- 

 sistance appears, following an attack of and 

 recovery from an infectious agent. It is mani- 

 fest in persons or animals that have recovered 

 from many forms of such invasion, or it may 

 appear as the result of measures purposely 

 taken in order to favor its development. In 



