CHAPTER VII. 



VACCINE THERAPY 



For centuries it has been known that following an attack of 

 certain acute infectious diseases there remains a certain loss of 

 susceptibility to the contraction of a second attack of the same 

 disease. Early in the eighteenth century this experience was 

 utilized by vaccination for small-pox. When it was found, about 

 the middle of the nineteenth century, that many acute and in- 

 fectious diseases have for their etiological factor certain micro- 

 organisms known as bacteria, attempts were made to induce im- 

 munity by inoculation of killed or attenuated cultures of these 

 organisms. Pasteur in this way successfully immunized against 

 chicken cholera, but while a certain amount of success by the 

 injection of killed cultures was obtained, still it was found imprac- 

 ticable for reasons that are not understood nor can be considered 

 here. Recently, however, Haffkine has successfully immunized or 

 vaccinated against cholera and Pfeiffer and Wright against ty- 

 phoid fever. It would prove impracticable to employ active im- 

 munization against all organisms with which man may be infected, 

 for this would require frequent injections of all kinds of organisms. 

 Active immunization to be applicable generally must be such that 

 it can be instituted after infection has occured. In this Pasteur 

 was successful in the disease of hydrophobia. It was found, how- 

 ever, that when the method of active immunization is begun after 

 infection has occured, there is a super imposition of a mild form 

 of the disease upon a severer form, thus accentuating the disease. 

 This observation lead to a relatively long period of cessation of 

 this method of treatment. 



In recent times active immunization after contraction of the 

 disease, has again become important. This has been due espec- 



