seeded in the microplates with seriol dilutions of the serum containing ifn and incubated overnight at 37 u00b0 c followed by removal of the serum the cells were challenged with vesicular stomatitis virus and overlayed with 0 5 methyl cellulose approximately 24 hours later the cells were each stained with a 1 solution of crystal violet and the number of plaques per well was counted the serum dilution required to reduce the number of plaques per well by 50 as compared to the virus control was finally converted to the international unit using a reference mouse interferon supplied by the u s national institute of health nih this interferon was induced with its peak at the time of about 24 hours after the intraperitoneal injection of th69e experiment 4 th69e was intraperitoneally injected to ddi male mice each group consisting of 5 mice having an average weight of 24 g in a dose of 150 15 and 1 5 mg kg of the weight of the mice in the same manner as in experiment 3 the reference mouce interferon was assayed with respect to the serums obtained 24 hours later table 3______________________________________ titer international unit of interferon induced per mldose of th69e of serum______________________________________150 mg kg 40 15 mg kg 160 1 5 mg kg 30saline lt 4______________________________________ in order to characterize interferon induced by the intraperitoneal injection of th69e to ddi mice in a dose of 15 mg kg of the weight.