ANTIGENIC PROPERTIES 109 



associated with a noninfectious fraction which sediments more 

 slowly than the virus. 



Efforts to isolate phage antigens by degradation of the virus 

 ])article have met with partial success (Lanni and Lanni, 1953; 

 DeMars, 1955; see also Hershey, 1955). 



9. Kinetics of Neutralization 



It had been recognized since the work of Prausnitz (1922) 

 that the neutralization of phage activity by antiserum was a 

 relatively slow process, and that a small proportion of the phage 

 population resisted inactivation by antibody. There seems to 

 have been no further attempt to study the kinetics of phage 

 neutralization until the work of Andrewes and Elford (1933a). 

 These authors systematically varied the concentrations of 

 antiserum and of phage in the reaction mixture, and determined 

 the decrease in the number of infectious phage particles as a 

 function of time. The "percentage law" is a summary of their 

 experimental results: "over a very wide range a given dilu- 

 tion of serum neutralized in a given time an approximately 

 constant percentage of phage, however much phage there was 

 present." This relationship held from concentrations of a 

 few hundred phage particles per ml. up to at least 10^ per ml., 

 and for serum concentrations from 10~^ to undiluted. Although 

 this relationship between phage and antibody is taken for granted 

 by phage workers today, it was very startling at the time of its 

 discovery, and its implications are still not understood or ap- 

 preciated by many immunologists and virologists. 



Burnet, Keogh, and Lush (1937) presented kinetic measure- 

 ments for the inactivation of various phages by antiserum. 

 In most cases the proportion of active virus decreased logarith- 

 mically with time after a slight initial lag. The rate of in- 

 activation was directly proportional to the concentration of 

 antiserum. The inactivation was assumed to be the result of a 

 collision between a phage particle and an antibody molecule. 

 Since the reaction is usually carried out in the presence of a 

 large excess of antibody, phage neutralization does not decrease 



