HISTORIC DEVELOPMENT OF IMMUNOLOGY 51 



Passive Immunization is brought about by the 

 introduction of immune bodies or antibodies 

 that have been formed by the tissues of actively 

 immunized individuals or animals and which are 

 contained in their blood-serum. In the practical 

 application of passive immunization, the immu- 

 nizing process is carried out by the injection 

 into an individual of blood-serum from actively 

 immunized animals. The individual, therefore, 

 receives the antibodies in a passive manner 

 that is, his tissue-cells are not called upon to 

 produce antibodies. Since blood-serum of an 

 immunized animal contains the antibodies and 

 is the usual vehicle by which they are trans- 

 ferred, the method of passive immunization is 

 called ''serum therapy." Passive immuniza- 

 tion may be employed for two purposes: (1) to 

 prevent disease, and (2) to treat disease. 



PROPHYLACTIC PASSIVE IMMUNIZATION 



In prophylactic passive immunization, the an- 

 tibodies are introduced into the tissue fluids of 

 the individual before infection has occurred, or 

 at least in the early stage of infection in order 

 to augment the natural protective powers of the 

 tissues before the infection has become suffi- 



