On the variation of the plaque size in the host-parasite system of the bacteriophage P84.

It has already been reported by Izeki and Sakai (1) (2) that S . newington is lysogenic and the bacteriophage liberated from this micro-organism transduces the antigenic structure of S. anatum (3.10) to that of S . newington (3.15). During the study of this transduction phenomenon, it was found that there was sometimes a mutant strain of S. anatum on which the bacteriophage liberated from S. newington produced very tiny plaques . Further studies revealed that the bacteriophage showed a longer latent period on this kind of mutant strains . The bacteriophage also splits off two kinds of mutant whose plaque sizes were different from those of the original bacteriophage if their plaques were produced on adequate host cells, and in these cases there seems to be some relationship between the plaque size and the latent period. Hershey(3) described a mutation of the bacteriophage concerned with plaque size, and later Doermann (4) stated that the latent period of the mutant whose plaque size has become larger than that of the original phage did not vary from that of the original. These findings suggest that there may not necessarily be any relation between the latent period and the plaque size . The present paper is dedicated to the description of the plaque size change seen in the host-parasite system of the bacteriophage liberated from S . newington.