Since the goal in studies of this sort was to examine the cell cycle properties of cells in exponentially growing cultures undergoing unrestricted growth, the technique for producing the synchrony must cause little if any disturbance to growth. At a minimum, it was required that the cells undergo at least two cycles of detectable synchrony, that whatever is observed in the first cycle repeats in the second, and that the fundamental properties of the synchronous cultures, such as cell sizes and growth rates, mimic the initial exponential-phase populations. All methods I tested caused some level of disturbance. Many methods produced a single burst of seemingly synchronized division after a delay period, but these were deemed to be nothing more than a reflection of the recovery from the sometimes harsh treatments employed. The method that appeared to cause the least disturbance involved filtration of a culture through a stack of Whatman cellulose filter papers. In this procedure, the smaller newborn cells pass through the stack into the effluent, and can be collected, while the larger, older cells are retained within the stack . With some modifications from the original reports, such as pressure rather than vacuum filtration, this technique enabled me to perform a few simple irradiation experiments on cells at very low concentrations.