118 BACTERIOPHAGES 



of about 4,600 antibody molecules (Hershey, Kalmanson, and 

 Bronfenbrenner, 1943b, Hershey, Kimura, and Bronfenbrenner 

 1947), not more than two or three molecules, and possibly only 

 one, actually participate in neutralization, regardless of how 

 many attach. 



3. Depending on the conditions of preparation, neutralized 

 phage may absorb to host cells normally, poorly, or not at all 

 (Burnet, Keogh, and Lush, 1 937 ; Hershey and Bronfenbrenner, 

 1952; Nagano and Mutai, 1954b; Nagano and Oda, 1955). It 

 may even adsorb to one host, which it proceeds to infect, but not 

 to another, for which it has been neutralized (Lanni and Lanni, 

 1957). A normal particle which has already adsorbed to a host 

 cell may or may not be resistant to neutralization. 



4. The tip of the phage tail is the site of adsorption to the 

 host (T. F. Anderson, 1952). 



5. Following adsorption of a normal phage particle, the 

 phage DNA enters the host cell, while the phage protein (ghost) 

 remains outside and can be stripped off without interfering with 

 phage reproduction (Hershey and Chase, 1952). Hence, infec- 

 tion consists in the injection of phage nucleic acid into the bac- 

 terium, this process being mediated by the phage tail in a way 

 which is not yet clear. Neutralized phage that succeeds in 

 adsorbing to a host cell does not inject its DNA (Nagano and 

 Oda, 1955; Tolmach, 1957). 



6. Neutralizing antibody is just one of several species of anti- 

 phage antibody. There is evidence that its action is confined to 

 the phage tail, while other antibodies react mainly with the 

 phage head (Lanni and Lanni, 1953). 



These observations clearly indicate that the phage tail is 

 critically important for neutralization. It would appear that 

 attachment of one or a few antibody molecules at appropriate 

 sites on the tail can render the virus noninfectious either by pre- 

 venting adsorption, or by interfering with injection if the virus 

 remains capable of adsorbing. Reaction of adsorbed virus with 

 antibody, after injection of the DNA, would have no consequence 

 for the infection. How antibody manages to prevent injection 



