Induced mutations in bacterial viruses

In another paper of this Symposium, to which ours is closely related and to which we refer the reader for a description of material and for terminology, Dr. Hershey (4) has described a variety of spontaneously occurring mutations of bacterial viruses. One class of mutations affects the type of plaque. These mutations occur in only one group of serologically related viruses, the group to which belong T2, T4, and T6. The most conspicuous of these mutations is the γ mutation. Our observations are concerned exclusively with this γ mutation. We have seen also some of the other mutations which affect the type of plaque and which Hershey has described, but we have not made systematic experiments concerning them.