108 BACTERIOPHAGES 



of the phage-neutralizing activity of the serum. The antibody- 

 blocking effect showed the serological specificity of phage CI 6. 

 The ultrafiltrate factor was not adsorbed by phage-sensitive 

 bacteria and had no bacteriolytic activity. It was relatively 

 heat resistant, requiring treatment at 90 ° C. for 30 minutes for 

 inactivation. On this basis Burnet suggested that it might be 

 a polysaccharide. 



DeMars, Luria, Fisher, and Levinthal (1953) demonstrated 

 the presence of similar specific soluble substances in bacteria 

 infected with coliphages T2, T4, or T5. The substances were 

 liberated from the infected bacteria during the latent period by 

 premature lysis, and were separated from phage particles and 

 bacteria by ultrafiltration through collodion filters. The quan- 

 tity of ultrafiltrable specific antigen increased during the latent 

 period. What is probably the same type of substance was lib- 

 erated from bacteria infected with phage T2 or T6, in which 

 normal phage development had been prevented by the addition 

 of proflavine (see also DeMars, 1955; Barry, 1954). The ultra- 

 filtrable fraction had the same serological specificity as the in- 

 fecting phage. At equivalent antibody-blocking activity the 

 ultrafiltrable fraction from T2 lysates had roughly the same 

 complement-fixing activity as intact virus (Lanni and Lanni, 

 1953). 



Crude T2 lysates contain a second noninfectious antibody- 

 blocking component, which appears to be intermediate in size 

 between the ultrafiltrable component and the infectious virus 

 particle (Lanni and Lanni, 1953; DeMars, 1955). The latter 

 reference should be consulted for details of the measurement of 

 antibody-blocking agents and for a description of their intra- 

 cellular development. Actually, the antibody-blocking meas- 

 urement may be regarded as an abbreviated absorption experi- 

 ment, in which the absorbing agent and its attached antibody 

 are allowed to remain in the system during subsequent measure- 

 ment of residual neutralizing activity. 



Lanni (1954) has found that at least one-half of the total 

 phagc-specific complement-fixing activity of T5 lysates is 



