The classic procedure that laid the foundation for the quantitative study of the life cycle of lytic bacterial viruses. A suspension of bacteria was mixed with enough viruses to ensure that a virus attached to each host cell. Free viruses were removed, and at periodic intervals thereafter aliquots were withdrawn and subjected to plaque assay (q.v.). The number of plaques per aliquot remained constant for an initial period of time. Aliquots taken after this latent period showed a progressive increase in plaque numbers. During this time, infected cells were lysing and liberating infectious phage, each capable of producing a plaque. Once all cells had lysed, a plateau was reached, and so the curve describing plaque counts during the experiment showed a single step. The eclipse period refers to the time between viral attachment and the assembly of the first progeny phage. It is during this period that replication and assembly of the phages is occurring. Cells must be artificially lysed to determine when the earliest infectious particles appear. The latent period is longer than the eclipse period because the host cell does not normally lyse until many progeny have been assembled. See Chronology, 1939, Ellis and Delbrück; burst size, plaque.
Subjects: Genetics and Genomics.