Chapter V 



METHODS OF IMMUNIZATION 



Active Immunization may be carried out (1) 

 with attenuated virus the attenuation being 

 obtained by heating, by drying, by passage 

 through animals, or by prolonged cultivation at 

 temperatures above the optimum; (2) with sub- 

 lethal amounts of virulent virus; (3) with killed 

 bacteria, (4) with bacterial products, or toxins, 

 and (5) with extracts of pollen. From a prac- 

 tical standpoint, the first, third and fifth meth- 

 ods only are used and are spoken of as "vaccine 

 therapy." Active immunization may be prac- 

 tised for two purposes: (1) for the prevention 

 of disease and (2) for the treatment of disease. 



PROPHYLACTIC ACTIVE IMMUNIZATION 



Prophylactic active immunization is accom- 

 plished by the production of immunity which is 

 held in reserve to overcome an infection if it 

 should occur. For example, immunity against 

 the virus of smallpox may be produced by inoc- 

 ulation with cowpox virus, so that for several 



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