Bacteriophages can be cultured on agar plates after being mixed with living host cells that are then spread out on the surface of the plate. As the confluent "lawn" of bacteria grow, any cell infected by a phage will lyse, resulting in the appearence of holes or plaques, representing the area where cells have been attacked and killed. By counting the number of plaques on a plate, researchers are able to mathematically calculate the original number of bacteriophages. This type of culture can also be used to speciate bacteria. Called "phage typing," the process uses bacteriophages that are specific for one type of bacterium.