Host Controlled Variation in Bacterial Viruses

Passage through new hosts or new tissues is a widely used method for altering the properties of viruses. In some instances selection of spontaneous mutants has been demonstrated to be the mechanism causing the variation (Luria, 1945). Nonhereditary mechanisms sometimes have been postulated, but since no such case has been analyzed sufficiently, it is often assumed that selection of mutants is the only possible mechanism. A detailed analysis of two cases of variation in two different bacterial viruses is reported in this paper. In both these cases we are dealing with nonheritable alterations stemming directly from passage through a new host and not with mutations. A somewhat similar case of host controlled variation involving other bacterial viruses has been reported recently by Luria and Human (1952).