Infectious center assays on demonstrating the loss of virus protection following Quillaja extract removal. The ability of reovirus or rotavirus to infect cells pretreated with Quillaja extract was tested. Cells were treated with Quillaja extract for 1 h and then the monolayers washed and fresh media added without Quillaja extract. This represents time 0. After 1, 2, 4, 8, 12, 16 and 24 h virus was added to these cells. The results are represented as the number of cells demonstrating active viral infection (plaques) when plated onto uninfected cell monolayers 1 h after virus addition. See materials and methods for details. These data are plotted as reovirus/L929 —□— (Ultra Dry 100 Q = 0 mg/ml), reovirus/L929 - - - □- - - (Ultra Dry 100 Q = 0.001 mg/ml), reovirus/L929 —△— (Vax Sap = 0 mg/ml), reovirus/L929 - - - △- - - (Vax Sap = 0.0001 mg/ml), rotavirus/MA104 —◆— (Ultra Dry 100 Q = 0 mg/ml), rotavirus/MA104 - - - ◆- - -(Ultra Dry 100 Q = 0.001 mg/ml), rotavirus/MA104 —0— (Vax Sap = 0 mg/ml), rotavirus/MA104 - - -0- - - (Vax Sap = 0.0001 mg/ml). These data from the treatment of reovirus with Ultra Dry 100 Q are new but generated by repeating experiments previously published [47]. The experiments were repeated and the data is included to permit a direct comparison to the new data presented for reovirus treated with Vax Sap and rotavirus treated with either Ultra Dry 100 Q or Vax Sap. PFU: Plaque-forming unit.