Pulse processing for analysis of cells for apoptosis: a dot plot of pulse area against pulse height of an asynchronous population of cells stained for DNA content with propidium iodide (A). Region R1 omits aggregated cells, seen below the region, and cell debris which is seen in the extreme bottom left hand corner. The histogram on the right shows an analysis of cells in gate R1. Gate f represents a background of apoptotic cells in an untreated cell population and does not include cell debris.