Abstract
(1) By superinfection of S-9 lysogenic cells with T-c200 temperate phage which is closely related to the carried prophage, a double lysogenic strain with the two prophages T-c200 and S-9 was obtained.
(2) This double lysogenic cell spontaneously liberated a new type of phage other than the two parental phages.
(3) This new type of phage seems to have originated from recombination of the genes controlling the host specificities of the two parental phages. This recombination seems to have occurred in the prophage stage and to represent the type proposed by Appleyard (1954).
