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Figure 2: pH dependence of 16-HBE cell survival, as measured by methylene blue absorption. *Exposure of cells to medium with pH 1.5 for 5 minutes resulted in significantly less cell proliferation after 20 hours of incubation compared to exposure to pH 2.5 (mean absorption 0.22 versus 0.57; , ). pH of control medium was 7.9. Histograms represent the means and the bars the SEM.