Ultraviolet irradiation of bacteriophage during intracellular growth

In the course of attempts to produce mutations in bacteriophage by ultra-violet irradiation of bacteria infected with the phage, we found that suppression of the ability of an infected bacterium to liberate phage required higher doses than either sterilization of noninfected bacteria or inactivation of free phage. The doses required to suppress phage liberation varied in the course of the interval between infection and liberation, during which intracellular phage growth takes place. These observations were in agreement with the fact that phage multiplication can take place in bacteria recently sterilized by irradiation (Anderson, 1944; Rouyer and Latarjet, 1946). They suggested that the ob-served effect of radiation on the infected bacteria might depend-on inactivation of intracellular phage. Variations of this effect might then reflect the changes in number and properties of phage particles during intracellular growth-that is, in the course of processes that lead to the production of over 100 phage par-ticles from each infected bacterium (Delbriick, 1946). An analysis of the changes in ultraviolet sensitivity during the period of intracellular growth coul