112 IMMUNOLOGY 



tical value for large scale immunization against typhus fever. The 

 subject of immunization against the virus of poliomyelitis is dis- 

 cussed in a later chapter. 



Burnett, Andrews and others have shown that immunity can 

 be induced in animals and man by the inoculation of influenza 

 virus by various means. There is some evidence (Burnett, 1937, 

 1938) that cultivation of influenza virus on chick embryos alters 

 its virulence without impairing its immunizing properties. Re- 

 cently Horsfall (1940-41) has prepared a complex virus vaccine 

 using influenza A virus and canine distemper virus X. The anti- 

 body response in ferrets and man has been much more adequate 

 than that from any of the other preparations previously used. 

 If this vaccine proves to be as successful in man it will be possible 

 to immunize both military and civil populations against this very 

 serious disease. Since there are a number of strains of influenza 

 virus (Smith and Andrews, 1938) it would seem that for general 

 use a polyvalent vaccine or one with broad antigenic powers 

 should be required. 



Jenner and his colleagues apparently failed to recognize the 

 underlying principles in the use of attenuated smallpox virus as 

 an immunizing agent. These principles and their broad biological 

 significance Avere disclosed by Pasteur in his studies made a century 

 after Jenner in 1879-80. 



Immunization With Attenuated Bacteria. — By accident or de- 

 sign Pasteur discovered that chickens inoculated with old or at- 

 tenuated cultures of the organisms of chicken cholera became im- 

 mune to subsequent infection with virulent strains. He had 

 previously noticed that animals recovering from experimental 

 anthrax were immune. It is quite likely that Jenner 's discovery 

 was a factor in enabling Pasteur to grasp the broad fundamental 

 principles involved and to establish the science of preventive in- 

 oculation or immunization upon a firm foundation. His success- 

 ful and spectacular immunization against anthrax and rabies, using 

 attenuated bacteria and virus respectively, placed protective vac- 

 cination upon a firm foundation. 



Since Pasteur's time the French school has clung tenaciously to 

 the principle of immunization with living attenuated organisms as 

 evidenced by the present use of the B.C.G. (Bacillus of Calmette 



