Abstract
1. When S4 bacteria were superinfected with temperate phage s2 which bears a close relationship serologically to the carried phage s4, a stable doubly lysogenic strain of S4 was successfully odtained experimentally.
2. From the culture of this bacterium a new type of phages possessing exchanged characters of both parents was obtained in addition to both parents s2 and s4. Under the assumption that these new type viruses (r1 and r2) resulted from the recombination of s2 and s4, the mechanism of the recombination of viruses from doubly lysogenic strain has been considered.
3. The above recombinants r1 and r2 resulting from genetic exchange between s2 and s4 possess the characters of each of the parents in plaque morphology, host-range, etc, and moreover the factor determining O[I] antigen. It may be, therefore, concluded that the factor controlling the O[I] antigen of bacteria is situated inside the gene constitution of phage.
