Abstract
A bacteriophage is described which grows on recipient (F-) and not on donor ( Hfr, F+, or F') salmonella. The reason for this differential is unknown, since the phage attaches to all mating types, but progeny ensue only from female bacteria. Purification of this phage has been accomplished. A procedure is described for quantitatively determining either the acquisition or loss of the F agent by bacteria.