FIG 2.

Examples of the experiments used to characterize membrane fusion activity and stability of influenza viruses. (a) Inhibition of viral infection by NH₄Cl. (b) pH dependence of virus-mediated hemolysis. (c) Virus inactivation at low pH. The experiments were performed as described in Materials and Methods. Each panel shows results of three replicate experiments performed either on the same day (a and c) or on different days (b) using the viruses A/swine/Marseille/2260/1980 (H1N1) (solid lines) and A/duck/Schleswig/21/1979 (H1N1) (dashed lines). For each replicate, the concentrations of NH₄Cl and values of pH treatments that caused 50% effect were determined from the curve by interpolation. All individual values were averaged (Table 1).