8 APPLIED IMMUNOLOGY 



Passive immunization signifies the process by 

 which immunity is acquired when artificial antisera are 

 injected into the animal body (see Chapter V) . Thus 

 the inoculated animal plays no part in the production 

 of the antibodies or antitoxin which he receives, and 

 the process is termed passive. Hence the animal is in- 

 jected with the specific cellular products (antitoxin) 

 of another animal previously actively immunized, and 

 by a process of simple neutralization the toxins in the 

 diseased animal are destroyed and immunity con- 

 ferred. In passive immunization the antibodies bear a 

 close chemical combination to the cells. The acquired 

 immunity of passive immunization is of vastly shorter 

 duration than that resulting from active immunization. 



Mechanism of the Production of Immunity 



There is a group of foreign chemical substances, 

 conveniently styled antigens, to which the animal body 

 reacts in a definite manner. This group must be dif- 

 ferentiated from and not confounded with the poison 

 group, as the common poisons are not antigens. The 

 group embraces the foreign proteins, including the 

 bacterial proteins, also certain complex and more or 

 less unknown bodies, as bacterial toxins, parenteral 

 proteolytic ferments, enzymes and other animal and 

 vegetable toxic substances. Following the subcutane- 

 ous, intra-abdominal or intravenous injection of an 



