54G F. M. BURNET 



At the present time the following statement does not seem to be invalidated 

 by any of the recorded work: 



(1) Virus neutrahzation by immune serum results from union of antibody 

 molecules with the virus surface. 



(2) These unions are of varying degrees of firmness depending on variations 

 (a) in the pojDiilation of antibody molecules, (b) in the disposition and access- 

 ibihty of binding sites on the viral surface, and (c) on steric factors operating 

 at the time of effective collision. 



(3) Different strains of virus show various degrees of immunological rela- 

 tionship, i.e., a proportion of a population of antibody molecules in anti-A 

 serum will demonstrably interact with virus of strain A^ and vice versa. In 

 genera], absorption with A^ wiE remove antibody reacting with this strain, 

 leaving antibody against the homologous strain little altered. The nature of 

 these "pattern" differences in antigen and antibody molecules is unknown 

 and introduces further opportunity for variabihty when reactions with anti- 

 sera not strictly homologous with the virus are studied. 



(4) With high concentrations of reagents, firm union, presumably with 

 denaturation of antibody globulin, takes place and, particularly when aggre- 

 gation occurs or is produced by centrifugation, antibody absorption is 

 demonstrable. 



(5) Destruction of infectivity by adsorbed antibody will vary according to 

 the susceptibility of the indicator host. It is probably not often dependent on 

 prevention of attachment to the susceptible cell surface, but too Httle is 

 known of the processes by which cell uifection is initiated to allow any 

 specific hypothesis. 



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