IMMUNITY 7 



difference in the susceptibility and resistance to the 

 various infections exist. Thus carnivorous animals 

 are highly resistant to glanders and anthrax, whereas 

 herbivorous animals are highly susceptible. This 

 resistance in carnivora may be explained by the 

 nature of the diet, as the carnivorous animals may 

 have gained a slow artificial immunity from eating 

 flesh contaminated with the organisms of the disease 

 to which they show such resistance. 



Acquired Immunity.— It is a matter of common 

 experience that many of the infectious diseases occur 

 but once in the same individual. This is notably the 

 case in most of the exanthemata ; resistance acquired 

 in this way is called " acquired immunity." 



Active Immunity : Active Artificial Immunity. — 

 The process of conferring protection by treatment 

 with either an attenuated form or sublethal quantity 

 of the infectious agent of a disease or its products 

 is spoken of as " active immunisation." There are 

 various methods by which this can be accomplished. 

 The following are the commonest : 



1. By the use of attenuated cultures. 



2. By the use of sublethal doses of fully virulent 

 bacteria. 



3. By the use of dead bacteria. 



4. By using bacterial products. 



Examples of the above methods in practice are : 

 (1) Immunisation against anthrax ; (2) present-day 

 method of vaccination against rabies ; (3) vaccines 

 used against strepto- and staphylococci infections ; 



