Aliquots of cell suspensions (3–6 ml, depending on the density of
the suspension) were placed in Petri dishes (Ø 50 mm). For
assaying the alkalinization response, the pH indicator chlorophenol
red (10 mM) was added. For assaying the oxidative burst, cells
were supplied with the peroxidase substrate 5-aminosalicylic acid
(100 mM). Using a narrow tipped pipette most of the medium was
removed, leaving a thin 1–2 mm thick layer of (wet) cells in the
dish. Test substances in a volume of 1 ml were applied locally onto
the lawn of cells, and the Petri dishes were analyzed optically by
a flat-bed scanner at intervals.