Evidence for a physical component to the radiation-induced bystander effect?

PURPOSE: The nature of the transferrable factor which goes from irradiated objects to bystander objects remains undefined. Most agree that a chemical entity is the likely 'factor' although some authors have produced in vitro evidence for the involvement of a physical component or a very potent volatile capable of traveling through air distances. In this paper we test the hypothesis that the communicated signal may be physical at least in part.