734 PASSIVE IMMUNIZATION SERUM THERAPY 



but we receive them passively in the form of an injection of an antibody- 

 laden serum. The antibodies are produced by active immunization of 

 some other animal, usually a horse, and we receive the antibodies or prod- 

 ucts of this immunization in a passive manner, i. e., our body-cells receive 

 protection against an infection and aid us in overcoming it through anti- 

 bodies produced in some other animal. For this reason the process is 

 called passive immunization; the particular kind of increased resistance 

 afforded against infection is known as passive immunity, and since blood- 

 serum contains the antibodies and is the usual vehicle by which they are 

 transferred, the method is called serum therapy. 



PURPOSES OF PASSIVE IMMUNIZATION 

 Passive immunization may be employed for two main purposes: 



1. To prevent disease (prophylactic immunization). 



2. To cure disease (curative immunization). 



In prophylactic immunization the antibodies are introduced into our 

 body-fluids before infection has actually occurred, or at least in the 

 earliest stage of infection, for the purpose of placing them on guard to 

 destroy the infecting microorganism or to neutralize its products before 

 it has had an opportunity to produce disease. In other words, we aim 

 to fortify our natural defenses by purchasing antibodies from another 

 animal. From the fact that these antibodies may be introduced in a 

 short space of time and that in this manner an immunity may be quickly 

 gained, passive immunization for prophylactic purposes is indicated 

 when the danger of infection is imminent, and when it is impossible, or 

 when there is not sufficient time, for us to stimulate our own body-cells 

 to produce our own antibodies by active immunization with a vaccine. 



Since the antibodies are produced in another animal, the serum, when 

 introduced into our body-fluids, represents a foreign protein, and, ac- 

 cordingly, we find that the antibodies are retained for relatively short 

 periods of time and are quickly eliminated or destroyed. In active 

 immunization, however, the antibodies are in native surroundings, and 

 our body-cells continue to produce them for some time after active 

 stimulation has ceased, in this manner insuring a higher degree of 

 immunity and one of longer duration. For purposes of prophylaxis, 

 therefore, active immunization is always more desirable than passive im- 

 munization; not infrequently the two forms are used simultaneously, 

 as the antibody-laden serum will afford instant protection, while the 

 vaccine is stimulating our body-cells to produce antibodies that will 



