HYPERSENSITIVENESS 529 



merous mixed reactions: hence it is probable that host variation 

 and other factors affect the results obtained. 



Hanks (1935) confirmed the Dienes phenomena but he con- 

 cluded that it is not necessary to inject the antigen into a tubercu- 

 lous focus. Zinsser, Enders, and Fothergill (1939, p. 429) ques- 

 tion Hanks' conclusion as to the latter point. 



In addition to these results which suggest that tuberculin al- 

 lergy in tuberculosis is mediated by an antigen-antibody mecha- 

 nism, there are the observations of Rich and his colleagues as 

 well as others before them that the tuberculous animals can be 

 desensitized to tuberculin. 



Summary of Evidence Indicating an Antigen-Antibody 

 Mechanism. — The evidence which seems to indicate that bacterial 

 hypersensitiveness due to infection is mediated by an antigen- 

 antibody mechanism may be summarized as follows : 



1. It results only from the presence of an antigenic complex, 

 the whole bacterial cell, or from the introduction of a tuberculin 

 such as MA- 100 within the tissues of the body. 



2. An incubation period comparable to that in anaphylactic sen- 

 sitization is present. 



3. The reaction is specific. 



4. The early skin reaction in animals sensitized to egg white 

 and other soluble proteins is similar to the tuberculin reaction in 

 tuberculous guinea pigs. 



5. In animals sensitized to the pneumococcus a typical tuber- 

 culin type of skin reaction can be demonstrated. 



6. Desensitization to tuberculin can be accomplished. 



One must admit that although the evidence just cited is strongly 

 suggestive it cannot be regarded as proof that antibodies partici- 

 ])atc in tlie 1ul)orcu]in skin reaction o])served in tuberculous ani- 

 mals. 



Aronson (1933) calls attention to a number of other explana- 

 tions that have been offered by various investigators. He says 

 that Bordet believes that the reaction may be due to an increased 

 affinit}^ of the tissues of a tuberculous animal for tuberculin ; Koch 

 assumes that tuberculin contains a necrotizing substance that is 

 especially toxic for the white cells of tuberculous animals; Babes 

 and Proca assume that it is a summation effect due to tuberculin 



