98 S. E. LUR1A AND R. DULBECCO 



Table 3 



Reactivation of phage T2 under various conditions 



Phage T2, containing 2X10 10 particles per ml, was irradiated for 35 seconds. Phages TO and 

 T4, containing 4X10 10 particles per ml, were irradiated for 30 seconds. Phages Tl and T5 con- 

 tained 3X10 10 particles per ml. The bacterial suspensions (B) and (B/6) contained 10 9 cells 

 per ml. 



(c) Concentrated lysates of phages TZ (or T4, or T6), whether fully active 

 or irradiated, can reactivate irradiated particles of any other T-even phage. 

 These phages are morphologically, serologically, and probably genetically 

 related, whereas T5 belongs to a fully separate group (Delbruck 1946). The 

 "factor" in the lysates appears to carry the same pattern of relatedness. It is 

 not produced by irradiation, since its presence can be proved in unirradiated 

 lysates by the technique of cross-reactivation. 



(d) Reactivation is independent of contact between phages prior to infection 

 of the host: a mixture of bacteria and phages gives the same amount of re- 

 activation independently of how long the phages have been together before 

 adding the bacteria. 



(e) Phage T4r purified by fast centrifugation (kindly supplied by Dr. T. 

 F. Anderson) shows both self-reactivation as a function of concentration in 

 the mixtures, and ability to reactivate phages TZ or T6. The factor, therefore, 

 is present in such a purified phage suspension. 



(f) Reactivation of phage TZ by lysates of T6, for example, only occurs in 

 presence of bacteria capable of adsorbing both phages. Inactive phage TZ in 

 presence of bacteria B/6, by which it is adsorbed, is not reactivated by T6, 

 which is not adsorbed, but is reactivated by T4, which is adsorbed. This proves 



271 



